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Applet Life Cycle in Java with Example

Applet in Java

Applet in Java is a special Java program that are primarily used in a internet programming.

Applet Life Cycle is very important to know in Java Applet Programming.

As we have already seen how to run program from command prompt, but there were no GUI.

To provide Graphical user interface(GUI) Java Applet is used.

Applet program runs on a web browser at client side. Applet program are used to make the web site more dynamic.

1 Life Cycle of Applet Stages

When the applet program is loaded is passes through several stages:

Born or initialization
Running
Idle  or stopped                                                                                                              
Dead or terminate

Born or initialization

Running

Idle or stopped

Dead or terminate

A Applet Born State

Also known as initialization state.

It is the first state of applet lifecycle.

Applet enters in a born/ initialization state when it is first loaded.

Applet moves in a born state when init() method of Applet class executes.

Applet initialization occurs once in a applet lifecycle.

Inside the init() method we initialize all the variables.

Syntax of init() method in Java Applet

public void init(){				
}

1 2	public void init(){ }

B Applet Running State

Applet enters in a running state from born state when a start() method of Applet class executes.

Running sates call automatically when the initialization phase completes.

Applet also comes in a running state from idle state when idle applet again get processor.

Running sates call automatically when the initialization phase completes.

Applet also comes in a running state from idle state when idle applet again get processor.

Syntax of start()

public void start(){				
}

1 2	public void start(){ }

C Applet Idle State

A running appletenters in a idle sate from running state when execution of start complete.

In a another words when we leave the page of running applet then automatically it enters in a idle sate from running state.

Applet moves in idle state when stop() method executes and it moves idle to running state when again start() calls.

Syntax of stop()

public void stop(){				
}

1 2	public void stop(){ }

D Applet Dead State

An applet is moved to dead state when we quit the web browser. When applet moves in a dead state it removed from memory.

The Applet will be terminate when destroy () method calls. In a applet lifecycle, applet terminates/destroys ones.

Syntax of destroy()

public void destroy(){				
}

1 2	public void destroy(){ }

E Applet Display State

The Display state executes immediately after when applet enters in a running state.

In this state we display the information on the output screen using paint() method.

public void paint(Graphics  g){						
}

1 2	public void paint(Graphics g){ }

2 Applet Life Cycle Program in Java Example

Lets see one program to demonstrate the life cycle of applet.

import java.applet.Applet;
import java.awt.Graphics;
/* 
<applet code="AppletLifeCycle.class" width="500" height="500"> 
</applet> 
 */
public class AppletLifeCycle extends Applet {
    String s;
    public void init() {
        s = "Welcome to Java Applet";
        System.out.println("Inside init method");
    }
    public void start() {
        System.out.println("Inside start method");
    }
    public void paint(Graphics g) {
        System.out.println("Inside paint method");
        g.drawString(s, 100, 100);
    }
    public void stop() {
        System.out.println("Inside stop method");
    }
    public void destroy() {
        System.out.println("Inside destroy method");
    }
}

import java.applet.Applet;

import java.awt.Graphics;

</applet>

public class AppletLifeCycle extends Applet {

String s;

public void init() {

s = "Welcome to Java Applet";

System.out.println("Inside init method");

}

public void start() {

System.out.println("Inside start method");

}

public void paint(Graphics g) {

System.out.println("Inside paint method");

g.drawString(s, 100, 100);

}

public void stop() {

System.out.println("Inside stop method");

}

public void destroy() {

System.out.println("Inside destroy method");

}

Compile and Run

>javac AppletLifeCycle.java
>appletviewer AppletLifeCycle.java

Applet Life Cycle in Java Example — Fig: Java Applet Life Cycle Example

Output At Console

Inside init method
Inside start method
Inside paint method
Inside stop method
Inside destroy method

Inside init method

Inside start method

Inside paint method

Inside stop method

Inside destroy method

On running Applet It will print first 3 line from output.

On closing applet it will call stop and destroy method.

init() method can be used to initialize various values and objects that are going to use in program.

Similarly to release resource we can use destroy().

Example: Write a program to read file and show in java applet.

import java.applet.Applet;
import java.awt.Graphics;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;


/* 
<applet code="AppletLifeCycle.class" width="800" height="800"> 
</applet> 
 */
public class AppletLifeCycle extends Applet {

    File file;
    Scanner scanner;

    public void init() {
        sb = new StringBuffer();
        file = new File("D:\\test.txt");
        System.out.println("Inside init method: created StringBuffer and File Object");
    }

    public void start() {
        System.out.println("Inside start method");
    }
    public void paint(Graphics g) {
        System.out.println("Inside paint method");
        try {
            int i = 0;
            scanner = new Scanner(file);
            while (scanner.hasNextLine()) {
                g.drawString(scanner.nextLine(), 100, 100 + i);
                i += 30;
            }
        } catch (FileNotFoundException ex) {
            System.out.println("Exception " + ex);
        }

        System.out.println("Reading file and showing at applet");
    }
    public void stop() {
        System.out.println("Inside stop method");
    }

    public void destroy() {
        scanner.close();
        System.out.println("Inside destroy method: closed scanner object");
    }
}

import java.applet.Applet;

import java.awt.Graphics;

import java.io.File;

import java.io.FileNotFoundException;

import java.util.Scanner;

</applet>

public class AppletLifeCycle extends Applet {

File file;

Scanner scanner;

public void init() {

sb = new StringBuffer();

file = new File("D:\\test.txt");

System.out.println("Inside init method: created StringBuffer and File Object");

}

public void start() {

System.out.println("Inside start method");

}

public void paint(Graphics g) {

System.out.println("Inside paint method");

try {

int i = 0;

scanner = new Scanner(file);

while (scanner.hasNextLine()) {

g.drawString(scanner.nextLine(), 100, 100 + i);

i += 30;

}

} catch (FileNotFoundException ex) {

System.out.println("Exception " + ex);

}

System.out.println("Reading file and showing at applet");

}

public void stop() {

System.out.println("Inside stop method");

}

public void destroy() {

scanner.close();

System.out.println("Inside destroy method: closed scanner object");

}

Output

Inside init method: created StringBuffer and File Object
Inside start method
Inside paint method
Reading file and showing at applet
Inside stop method
Inside destroy method: closed scanner object

Inside init method: created StringBuffer and File Object

Inside start method

Inside paint method

Reading file and showing at applet

Inside stop method

Inside destroy method: closed scanner object

Fig: Reading File in showing in an applet

Sum of two numbers using command line arguments in java

Command line argument is as a way to pass arguments in java while running java program.

1 Sum of two integer numbers using command line arguments in java

Steps to add two integer numbers is below

Read command-line variable array args[0] and args[1].
Convert it to integer value and store it in two variables.
add both variables and store in another variable sum
print the sum.

public class CommandLineArguments {
    public static void main(String[] args) {
        int a = Integer.parseInt(args[0]);
        int b = Integer.parseInt(args[1]);
        int sum = a + b;
        System.out.println("Sum is " + sum);
    }
}

public class CommandLineArguments {

public static void main(String[] args) {

int a = Integer.parseInt(args[0]);

int b = Integer.parseInt(args[1]);

int sum = a + b;

System.out.println("Sum is " + sum);

}

Run above program from command prompt

>javac CommandLineArguments.java

>java CommandLineArguments 8 5

Output

Sum is 13

Sum is 13

value 8 will pass to args[0] and value 5 will store in args[1].

As we know args is String array.

So to convert value from string we used Integer.parseInt() method.

Lets see another example

2 Sum of two double numbers using command line arguments in java

public class CommandLineArguments1 {

    public static void main(String[] args) {
        double a = Double.parseDouble(args[0]);
        double b = Double.parseDouble(args[1]);
        double sum = a + b;
        System.out.println("Sum is " + sum);

    }
}

public class CommandLineArguments1 {

public static void main(String[] args) {

double a = Double.parseDouble(args[0]);

double b = Double.parseDouble(args[1]);

double sum = a + b;

System.out.println("Sum is " + sum);

}

Output

Sum is 13.0

1	Sum is 13.0

Similar way we can add long, float values.

You have to know how to convert string to long and string to float and from string to other data types.

This is possible with the use of Java wrapper classes.

Each primitive data type has its own class that is known as wrapper class.

Wrapper class contain methods to convert value from string to specify object type.

Following Classes are sub class of Number class.

You can find details in the Number class also check all its sub-classes.

3 Conversion from String to number using Wrapper class

Sr No	Convert from string to	Method
1	Byte	Byte.ParseByte()
2	Short	Short.valueOf()
3	Integer	Integer.shortInt()
4	Long	Long.parseLong()
5	Float	Float.parseFloat()
6	Double	Double.parseDouble()

Above programs are very simple.

Lets assume a situation if use does not provide two values or provides values like alphabet then how to deal with it.

4 How to check length of command line argument

Before addition we should check whether user has provided tow numbers or not.

Lets check it.

public class CommandLineArguments1 {

    public static void main(String[] args) {
        if (args.length != 2) {
            System.out.println("Please provide two arguments");
            System.exit(0);
        }
        double a = Double.parseDouble(args[0]);
        double b = Double.parseDouble(args[1]);
        double sum = a + b;
        System.out.println("Sum is " + sum);

    }
}

public class CommandLineArguments1 {

public static void main(String[] args) {

if (args.length != 2) {

System.out.println("Please provide two arguments");

System.exit(0);

}

double a = Double.parseDouble(args[0]);

double b = Double.parseDouble(args[1]);

double sum = a + b;

System.out.println("Sum is " + sum);

}

Output

>javac CommandLineArguments1.java
Sum is 9.0

>java CommandLineArguments1
Please provide two arguments

>javac CommandLineArguments1.java

Sum is 9.0

>java CommandLineArguments1

Please provide two arguments

args is string array so we can use length property to check its length.

if (args.length != 2) then we are showing a message to the user that Please provide two arguments and terminating the execution.

5 Exception handling with command line arguments

A. Handling ArrayIndexOutOfBoundsException

This exception occurs because we tried to access array index that does not exists.

Exception Handling try catch finally blocks in Java
Exception Handling in Java: Hierarchy Example and Types
User-Defined (Custom) Exceptions in Java with Examples

If user passed only one value and we accessing first tow value then this error can occurs.

To avoid this we already seen above validation problem.

Lets again run our first program and pass only one value

public class CommandLineArgument {

    public static void main(String[] args) {
        int a = Integer.parseInt(args[0]);
        int b = Integer.parseInt(args[1]);
        int sum = a + b;
        System.out.println("Sum is " + sum);

    }
}

public class CommandLineArgument {

public static void main(String[] args) {

int a = Integer.parseInt(args[0]);

int b = Integer.parseInt(args[1]);

int sum = a + b;

System.out.println("Sum is " + sum);

}

Output

>javac CommandLineArgument.java
>java CommandLineArgument 5

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 1 out of bounds for length 1
	at CommandLineArgument.main(CommandLineArgument.java:5)

>javac CommandLineArgument.java

>java CommandLineArgument 5

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 1 out of bounds for length 1

at CommandLineArgument.main(CommandLineArgument.java:5)

Lets see how to handle with exception

public class CommandLineArgument {

    public static void main(String[] args) {
        try{
            int a = Integer.parseInt(args[0]);
        int b = Integer.parseInt(args[1]);
        int sum = a + b;
        System.out.println("Sum is " + sum);
        }catch(ArrayIndexOutOfBoundsException e){
            System.out.println("Provide two values for addition");
        }
    }
}

public class CommandLineArgument {

public static void main(String[] args) {

try{

int a = Integer.parseInt(args[0]);

int b = Integer.parseInt(args[1]);

int sum = a + b;

System.out.println("Sum is " + sum);

}catch(ArrayIndexOutOfBoundsException e){

System.out.println("Provide two values for addition");

}

Output

>javac CommandLineArgument.java
>java CommandLineArgument 5

Provide two values for addition

>javac CommandLineArgument.java

>java CommandLineArgument 5

Provide two values for addition

Result

B. Handling NumberFormatException

This exception occurs when method is unable to convert string to a number type.

For example, a user gives “w” as input so the method is unable to convert it to a number.

Then this method will throw NumberFormatException.

Output

javac CommandLineArgument.java
>java CommandLineArgument w  e
Exception in thread "main" java.lang.NumberFormatException: For input string: "w"
	at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
	at java.base/java.lang.Integer.parseInt(Integer.java:652)
	at java.base/java.lang.Integer.parseInt(Integer.java:770)
	at CommandLineArgument.main(CommandLineArgument.java:4)

javac CommandLineArgument.java

>java CommandLineArgument w e

Exception in thread "main" java.lang.NumberFormatException: For input string: "w"

at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)

at java.base/java.lang.Integer.parseInt(Integer.java:652)

at java.base/java.lang.Integer.parseInt(Integer.java:770)

at CommandLineArgument.main(CommandLineArgument.java:4)

To resolve NumberFormatException again we will use try catch block.

public class CommandLineArgument {

    public static void main(String[] args) {
       try{
        int a = Integer.parseInt(args[0]);
        int b = Integer.parseInt(args[1]);
        int sum = a + b;
        System.out.println("Sum is " + sum);
       }catch(NumberFormatException e){
           System.out.println("Please Provide numbers as argument");
       }
        
    }
}

public class CommandLineArgument {

public static void main(String[] args) {

try{

int a = Integer.parseInt(args[0]);

int b = Integer.parseInt(args[1]);

int sum = a + b;

System.out.println("Sum is " + sum);

}catch(NumberFormatException e){

System.out.println("Please Provide numbers as argument");

}

Output

 >javac CommandLineArgument.java
>java CommandLineArgument w  e


Please Provide numbers as argument
>javac CommandLineArgument.java
>java CommandLineArgument w  e
Sum is 7

>javac CommandLineArgument.java

>java CommandLineArgument w e

Please Provide numbers as argument

>javac CommandLineArgument.java

>java CommandLineArgument w e

Sum is 7

C. Handling Multiple Exceptions

try can throw multiple exceptions to handle this we can create multiple catch blocks each for a specific exception.

We can also use one catch block to handle multiple exceptions.

public class CommandLineArgument {

    public static void main(String[] args) {
       try{
        int a = Integer.parseInt(args[0]);
        int b = Integer.parseInt(args[1]);
        int sum = a + b;
        System.out.println("Sum is " + sum);
       }catch(ArrayIndexOutOfBoundsException e){
            System.out.println("Provide two values for addition");
        }catch(NumberFormatException e){
           System.out.println("Please Provide numbers as argument");
       }
        
    }
}

public class CommandLineArgument {

public static void main(String[] args) {

try{

int a = Integer.parseInt(args[0]);

int b = Integer.parseInt(args[1]);

int sum = a + b;

System.out.println("Sum is " + sum);

}catch(ArrayIndexOutOfBoundsException e){

System.out.println("Provide two values for addition");

}catch(NumberFormatException e){

System.out.println("Please Provide numbers as argument");

}

Using StringBuffer or StringBuilder class

import java.util.Scanner;
public class ReverseString {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter a String");
        String string = scanner.next();
        StringBuilder sb = new StringBuilder(string);
        String reverseString = sb.reverse().toString();
        System.out.println("Your String is " + string);
        System.out.println("Reverse String is " + reverseString);
    }
}

import java.util.Scanner;

public class ReverseString {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

System.out.println("Enter a String");

String string = scanner.next();

StringBuilder sb = new StringBuilder(string);

String reverseString = sb.reverse().toString();

System.out.println("Your String is " + string);

System.out.println("Reverse String is " + reverseString);

}

Output

Enter a String
Programming
Your String is Programming
Reverse String is gnimmargorP

Enter a String

Programming

Your String is Programming

Reverse String is gnimmargorP

Using Loops(Iteration)

Copy and reverse the string

import java.util.Scanner;
public class ReverseStringExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter a String");
        String string = scanner.next();
        char[] c = string.toCharArray();
        char[] r = new char[c.length];
        int i = c.length - 1;
        int j = 0;
        while (i >= 0) {
            r[j] = c[i];
            i--;
            j++;
        }
        String reverseString = new String(r);
        System.out.println("String is " + string);
        System.out.println("Reverse string is " + reverseString);
    }
}

import java.util.Scanner;

public class ReverseStringExample {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

System.out.println("Enter a String");

String string = scanner.next();

char[] c = string.toCharArray();

char[] r = new char[c.length];

int i = c.length - 1;

int j = 0;

while (i >= 0) {

r[j] = c[i];

i--;

j++;

}

String reverseString = new String(r);

System.out.println("String is " + string);

System.out.println("Reverse string is " + reverseString);

}

Here getting input from user

converted into character array using toCharArray() of String

Initialize the other character array with same length as c character array.

Loop char array c in reverse order and r in forward order.

this will copy character array c in reverse order to r.

converted char array r to String

print both character array

Output

Enter a String
Java
String is Java
Reverse string is avaJ

Enter a String

Java

String is Java

Reverse string is avaJ

JLabel in Java Swing with Method Constructors and Examples

JLabel in Java Swing is an object that is used to display text and images in a Frame.

Jlabel uses to display information, show different messages, and make the frame interactive and readable.

JLabel class declaration

public class JLabel
extends JComponent
implements SwingConstants, Accessible

public class JLabel

extends JComponent

implements SwingConstants, Accessible

JLabel extends JComponent and implements SwingConstants and Accessible Interfaces.

JLabel Constructors

Sr No	Constructor and Description
1	JLabel() Create a Jlabel with no image and empty text
2	JLabel(String text) Create a Jlabel with specified text
3	JLabel(String text, int horizontalAlignment) Create a Jlabel with specified text and horizontalAlignment
4	JLabel(String text, Icon icon, int horizontalAlignment) Create a Jlabel with specified text, image and horizontalAlignment
5	JLabel(Icon image) Create a Jlabel with specified image
6	JLabel(Icon image, int horizontalAlignment) Create a Jlabel with specified image and horizontalAlignment

Commonly used JLabel Methods

Sr No	Method and Description
1	String getText() Get the text of label
2	void setText(String text) Set the text of label
3	Icon getIcon() Return the Graphic Icon of label
4	void setIcon(Icon icon) Set the graphic icon for label
5	void setHorizontalAlignment(int alignment) Set Horizontal alignment of label
6	int getHorizontalAlignment() Get Horizontal alignment of label
5	void setVerticalAlignment(int alignment) Set Vertical alignment of label
6	int getVerticalAlignment() Get Vertical alignment of label

JLabel contains more methods we have used a few of them here.

jlabel java Examples

import java.awt.Container;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class JLabelExample1 extends JFrame {

    Container container;
    JLabel label1, label2;

    public JLabelExample1() {

        container = this.getContentPane();
        container.setLayout(null);

        label1 = new JLabel("Welcome to Java");
        label1.setBounds(20, 40, 150, 40);
        container.add(label1);
        label2 = new JLabel("Learn with examples");
        label2.setBounds(20, 80, 150, 40);
        container.add(label2
        );

    }

    public static void main(String[] args) {
        JLabelExample1 frame = new JLabelExample1();
        frame.setTitle("Label Example");
        frame.setVisible(true);
        frame.setBounds(250, 100, 520, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
    }

}

import java.awt.Container;

import javax.swing.JFrame;

import javax.swing.JLabel;

public class JLabelExample1 extends JFrame {

Container container;

JLabel label1, label2;

public JLabelExample1() {

container = this.getContentPane();

container.setLayout(null);

label1 = new JLabel("Welcome to Java");

label1.setBounds(20, 40, 150, 40);

container.add(label1);

label2 = new JLabel("Learn with examples");

label2.setBounds(20, 80, 150, 40);

container.add(label2

);

}

public static void main(String[] args) {

JLabelExample1 frame = new JLabelExample1();

frame.setTitle("Label Example");

frame.setVisible(true);

frame.setBounds(250, 100, 520, 300);

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setResizable(false);

}

Label in java Example- How to change jlabel background color

import java.awt.Color;
import java.awt.Container;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class JLabelExample2 extends JFrame {
    
    Container container;
    JLabel label1, label2, label3, label4;
    
    public JLabelExample2() {
        
        container = this.getContentPane();
        container.setLayout(null);
        
        label1 = new JLabel("This is an Error message");
        label1.setBounds(20, 40, 250, 40);
        label1.setBackground(Color.red);
        label1.setOpaque(true);
        container.add(label1);
        label2 = new JLabel("This is a success message");
        label2.setBounds(20, 100, 250, 40);
        label2.setBackground(Color.GREEN);
        label2.setOpaque(true);
        container.add(label2);
        label3 = new JLabel("This is an info message");
        label3.setBounds(20, 160, 250, 40);
        label3.setBackground(Color.BLUE);
        label3.setOpaque(true);
        container.add(label3);
        label4 = new JLabel("This is a warning message");
        label4.setBounds(20, 220, 250, 40);
        label4.setBackground(Color.YELLOW);
        label4.setOpaque(true);
        container.add(label4);
        
    }
    
    public static void main(String[] args) {
        JLabelExample2 frame = new JLabelExample2();
        frame.setTitle("Label Example");
        frame.setVisible(true);
        frame.setBounds(250, 100, 520, 320);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
    }   
}

import java.awt.Color;

import java.awt.Container;

import javax.swing.JFrame;

import javax.swing.JLabel;

public class JLabelExample2 extends JFrame {

Container container;

JLabel label1, label2, label3, label4;

public JLabelExample2() {

container = this.getContentPane();

container.setLayout(null);

label1 = new JLabel("This is an Error message");

label1.setBounds(20, 40, 250, 40);

label1.setBackground(Color.red);

label1.setOpaque(true);

container.add(label1);

label2 = new JLabel("This is a success message");

label2.setBounds(20, 100, 250, 40);

label2.setBackground(Color.GREEN);

label2.setOpaque(true);

container.add(label2);

label3 = new JLabel("This is an info message");

label3.setBounds(20, 160, 250, 40);

label3.setBackground(Color.BLUE);

label3.setOpaque(true);

container.add(label3);

label4 = new JLabel("This is a warning message");

label4.setBounds(20, 220, 250, 40);

label4.setBackground(Color.YELLOW);

label4.setOpaque(true);

container.add(label4);

}

public static void main(String[] args) {

JLabelExample2 frame = new JLabelExample2();

frame.setTitle("Label Example");

frame.setVisible(true);

frame.setBounds(250, 100, 520, 320);

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setResizable(false);

}

JLabel Example – Foreground and background color change

package swing;

import java.awt.Color;
import java.awt.Container;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class JLabelExample3 extends JFrame {

    Container container;
    JLabel label1, label2, label3, label4, label5;

    public JLabelExample3() {

        container = this.getContentPane();
        container.setLayout(null);

        label1 = new JLabel("This is an Error message");
        label1.setBounds(20, 10, 250, 40);
        label1.setForeground(Color.red);
        container.add(label1);
        label2 = new JLabel("This is a success message");
        label2.setBounds(20, 60, 250, 40);
        label2.setForeground(new Color(0, 128, 0));
        container.add(label2);
        label3 = new JLabel("This is an info message");
        label3.setBounds(20, 110, 250, 40);
        label3.setForeground(Color.BLUE);
        container.add(label3);
        label4 = new JLabel("This is a warning message");
        label4.setBounds(20, 160, 250, 40);
        label4.setForeground(Color.decode("#FFA500"));
        container.add(label4);

        label5 = new JLabel("This is a Test message");
        label5.setBounds(20, 210, 250, 40);
        label5.setBackground(Color.BLACK);
        label5.setForeground(Color.WHITE);
        label5.setOpaque(true);
        container.add(label5);

    }

    public static void main(String[] args) {
        JLabelExample3 frame = new JLabelExample3();
        frame.setTitle("Label Example");
        frame.setVisible(true);
        frame.setBounds(250, 100, 520, 320);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
    }
}

package swing;

import java.awt.Color;

import java.awt.Container;

import javax.swing.JFrame;

import javax.swing.JLabel;

public class JLabelExample3 extends JFrame {

Container container;

JLabel label1, label2, label3, label4, label5;

public JLabelExample3() {

container = this.getContentPane();

container.setLayout(null);

label1 = new JLabel("This is an Error message");

label1.setBounds(20, 10, 250, 40);

label1.setForeground(Color.red);

container.add(label1);

label2 = new JLabel("This is a success message");

label2.setBounds(20, 60, 250, 40);

label2.setForeground(new Color(0, 128, 0));

container.add(label2);

label3 = new JLabel("This is an info message");

label3.setBounds(20, 110, 250, 40);

label3.setForeground(Color.BLUE);

container.add(label3);

label4 = new JLabel("This is a warning message");

label4.setBounds(20, 160, 250, 40);

label4.setForeground(Color.decode("#FFA500"));

container.add(label4);

label5 = new JLabel("This is a Test message");

label5.setBounds(20, 210, 250, 40);

label5.setBackground(Color.BLACK);

label5.setForeground(Color.WHITE);

label5.setOpaque(true);

container.add(label5);

}

public static void main(String[] args) {

JLabelExample3 frame = new JLabelExample3();

frame.setTitle("Label Example");

frame.setVisible(true);

frame.setBounds(250, 100, 520, 320);

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setResizable(false);

}

Jlabel set font Example – Set JLable font Size, Font Height

import java.awt.Color;
import java.awt.Container;
import java.awt.Font;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class JLabelExample4 extends JFrame {

    Container container;
    JLabel label1, label2, label3;

    public JLabelExample4() {

        container = this.getContentPane();
        container.setLayout(null);

        label1 = new JLabel("Hello Friends");
        label1.setBounds(20, 10, 250, 40);
        label1.setFont(new Font(Font.MONOSPACED, Font.PLAIN, 32));
        container.add(label1);
        label2 = new JLabel("Learn Java");
        label2.setBounds(20, 60, 250, 40);
        label2.setForeground(new Color(0, 128, 0));
        label2.setFont(new Font("Verdana", Font.BOLD, 30));
        container.add(label2);
        label3 = new JLabel("This is an italic Font");
        label3.setBounds(20, 110, 250, 40);
        label3.setFont(new Font("Arial", Font.ITALIC, 16));
        container.add(label3);
    }

    public static void main(String[] args) {
        JLabelExample4 frame = new JLabelExample4();
        frame.setTitle("Label Example");
        frame.setVisible(true);
        frame.setBounds(250, 100, 520, 320);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
    }

}

import java.awt.Color;

import java.awt.Container;

import java.awt.Font;

import javax.swing.JFrame;

import javax.swing.JLabel;

public class JLabelExample4 extends JFrame {

Container container;

JLabel label1, label2, label3;

public JLabelExample4() {

container = this.getContentPane();

container.setLayout(null);

label1 = new JLabel("Hello Friends");

label1.setBounds(20, 10, 250, 40);

label1.setFont(new Font(Font.MONOSPACED, Font.PLAIN, 32));

container.add(label1);

label2 = new JLabel("Learn Java");

label2.setBounds(20, 60, 250, 40);

label2.setForeground(new Color(0, 128, 0));

label2.setFont(new Font("Verdana", Font.BOLD, 30));

container.add(label2);

label3 = new JLabel("This is an italic Font");

label3.setBounds(20, 110, 250, 40);

label3.setFont(new Font("Arial", Font.ITALIC, 16));

container.add(label3);

}

public static void main(String[] args) {

JLabelExample4 frame = new JLabelExample4();

frame.setTitle("Label Example");

frame.setVisible(true);

frame.setBounds(250, 100, 520, 320);

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setResizable(false);

}

JLabel Example to getAttributes

import java.awt.Container;
import java.awt.Font;
import java.awt.font.TextAttribute;
import java.util.HashMap;
import java.util.Map;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class JLabelExample5 extends JFrame {

    Container container;
    JLabel label1, label2;

    public JLabelExample5() {

        container = this.getContentPane();
        container.setLayout(null);

        label1 = new JLabel("Do You Know about Java Labels?");
        label1.setBounds(20, 10, 520, 40);
        Font font1 = label1.getFont();
        Map<TextAttribute, Object> attribute1 = new HashMap<>(font1.getAttributes());
        attribute1.put(TextAttribute.FAMILY, "Cambria");
        attribute1.put(TextAttribute.SIZE, 20);
        label1.setFont(font1.deriveFont(attribute1));
        container.add(label1);

        label2 = new JLabel("What is Java");
        label2.setBounds(20, 60, 520, 40);
        Font font2 = label2.getFont();
        Map<TextAttribute, Object> attribute2 = new HashMap<>(font2.getAttributes());
        attribute2.put(TextAttribute.FAMILY, "Cambria");
        attribute2.put(TextAttribute.UNDERLINE, TextAttribute.UNDERLINE_ON);
        label2.setFont(font2.deriveFont(attribute2));
        container.add(label2);

    }

    public static void main(String[] args) {
        JLabelExample5 frame = new JLabelExample5();
        frame.setTitle("Label Example");
        frame.setVisible(true);
        frame.setBounds(250, 100, 520, 320);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
    }

}

import java.awt.Container;

import java.awt.Font;

import java.awt.font.TextAttribute;

import java.util.HashMap;

import java.util.Map;

import javax.swing.JFrame;

import javax.swing.JLabel;

public class JLabelExample5 extends JFrame {

Container container;

JLabel label1, label2;

public JLabelExample5() {

container = this.getContentPane();

container.setLayout(null);

label1 = new JLabel("Do You Know about Java Labels?");

label1.setBounds(20, 10, 520, 40);

Font font1 = label1.getFont();

Map<TextAttribute, Object> attribute1 = new HashMap<>(font1.getAttributes());

attribute1.put(TextAttribute.FAMILY, "Cambria");

attribute1.put(TextAttribute.SIZE, 20);

label1.setFont(font1.deriveFont(attribute1));

container.add(label1);

label2 = new JLabel("What is Java");

label2.setBounds(20, 60, 520, 40);

Font font2 = label2.getFont();

Map<TextAttribute, Object> attribute2 = new HashMap<>(font2.getAttributes());

attribute2.put(TextAttribute.FAMILY, "Cambria");

attribute2.put(TextAttribute.UNDERLINE, TextAttribute.UNDERLINE_ON);

label2.setFont(font2.deriveFont(attribute2));

container.add(label2);

}

public static void main(String[] args) {

JLabelExample5 frame = new JLabelExample5();

frame.setTitle("Label Example");

frame.setVisible(true);

frame.setBounds(250, 100, 520, 320);

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setResizable(false);

}

How to Show Image in JLabel

import java.awt.Container;
import java.awt.Image;
import java.io.IOException;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class JLabelExample5 extends JFrame {

    Container container;
    JLabel label1, label2, label3;
    ImageIcon ii1, ii2, ii3;
    URL url;
    Image image;

    public JLabelExample5() {

        container = this.getContentPane();
        container.setLayout(null);

        ii1 = new ImageIcon("d://javaicon1.png");
        label1 = new JLabel();
        label1.setIcon(ii1);
        label1.setBounds(20, 10, 50, 40);
        label1.setOpaque(true);
        container.add(label1);

        ii2 = new ImageIcon("d://javaicon2.gif");
        label2 = new JLabel();
        label2.setIcon(ii2);
        label2.setBounds(100, 10, 200, 200);
        label2.setOpaque(true);
        container.add(label2);

        try {
            url = new URL("http://placehold.it/120x120&text=TestIt");
            image = ImageIO.read(url);
        } catch (IOException ex) {
            System.out.println("Exception ");
        }
        ii3 = new ImageIcon(image);
        label3 = new JLabel("Place It");
        label3.setIcon(ii3);
        label3.setBounds(320, 10, 200, 200);
        label3.setOpaque(true);
        container.add(label3);
    }

    public static void main(String[] args) {
        JLabelExample5 frame = new JLabelExample5();
        frame.setTitle("Label Example");
        frame.setVisible(true);
        frame.setBounds(250, 100, 520, 320);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
    }

}

import java.awt.Container;

import java.awt.Image;

import java.io.IOException;

import java.net.URL;

import javax.imageio.ImageIO;

import javax.swing.ImageIcon;

import javax.swing.JFrame;

import javax.swing.JLabel;

public class JLabelExample5 extends JFrame {

Container container;

JLabel label1, label2, label3;

ImageIcon ii1, ii2, ii3;

URL url;

Image image;

public JLabelExample5() {

container = this.getContentPane();

container.setLayout(null);

ii1 = new ImageIcon("d://javaicon1.png");

label1 = new JLabel();

label1.setIcon(ii1);

label1.setBounds(20, 10, 50, 40);

label1.setOpaque(true);

container.add(label1);

ii2 = new ImageIcon("d://javaicon2.gif");

label2 = new JLabel();

label2.setIcon(ii2);

label2.setBounds(100, 10, 200, 200);

label2.setOpaque(true);

container.add(label2);

try {

url = new URL("http://placehold.it/120x120&text=TestIt");

image = ImageIO.read(url);

} catch (IOException ex) {

System.out.println("Exception ");

}

ii3 = new ImageIcon(image);

label3 = new JLabel("Place It");

label3.setIcon(ii3);

label3.setBounds(320, 10, 200, 200);

label3.setOpaque(true);

container.add(label3);

}

public static void main(String[] args) {

JLabelExample5 frame = new JLabelExample5();

frame.setTitle("Label Example");

frame.setVisible(true);

frame.setBounds(250, 100, 520, 320);

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setResizable(false);

}

double array java- java double array declare initialize access

Double array java is a Java array with double values.

All values are stored in contineous memory location

Declaring double array in Java

General syntax to declare array is

dataType [] arrayName;

dataType: Any primitive or user-defined data types like int, char, float, double. etc

[] : notation to represent an array.

arrayName: name of an array;

double[] d;

double[] price;

here d and price are arrays that can refer to the array of double type.

Initializing and Accessing double array in Java

initialization specifies the size and initial values of an array.

Syntax of initialization is

dataType [] arrayName=new dataType[SIZE];

dataType [] arrayName=new dataType[]{value1, value2, …. ,value n};

double[] d=new double[5];

double[] price=new double[4];

above two statements will allocate memory for two array that are pointed by d and price.

Initialize both arrays by value 0.0 (the default value of double data type).

We can also provide some initial value to the array as follows

double[] d=new double[]{2.3,5.4,7.6,8.9,9.9};

public class MyDoubleArray {
    public static void main(String args[]) {
    double[] d=new double[]{2.3,5.4,7.6,8.9,9.9};

    for(double a:d){
        System.out.println(a);
    }
    }
}

public class MyDoubleArray {

public static void main(String args[]) {

double[] d=new double[]{2.3,5.4,7.6,8.9,9.9};

for(double a:d){

System.out.println(a);

}

2.3
5.4
7.6
8.9
9.9

2.3

5.4

7.6

8.9

9.9

another way to initialize array is

double[] d={2.3,5.4,7.6,8.9,9.9};

Java Array Loop Initialization

import java.util.Scanner;

public class MyDoubleArray {
    public static void main(String args[]) {
    double[] d=new double[5];
    
    System.out.println("Enter the values for array");
    Scanner sc=new Scanner(System.in);
    
    for(int i=0;i<d.length;i++){
        d[i]=sc.nextDouble();
    }
     System.out.println("Array values are");
    for(double a:d){
        System.out.println(a);
    }
    }
}

import java.util.Scanner;

public class MyDoubleArray {

public static void main(String args[]) {

double[] d=new double[5];

System.out.println("Enter the values for array");

Scanner sc=new Scanner(System.in);

for(int i=0;i<d.length;i++){

d[i]=sc.nextDouble();

}

System.out.println("Array values are");

for(double a:d){

System.out.println(a);

}

Enter the values for array
12.3 
45.3 
66.5 
77.5 
78.7
Array values are
12.3
45.3
66.5
77.5
78.7

Enter the values for array

12.3

45.3

66.5

77.5

78.7

Array values are

12.3

45.3

66.5

77.5

78.7

Initializing Array using Arrays.fill()

Some times we need to fill array using same value that we can use fill method as below.

double[] d=new double[5];
Arrays.fill(d,4.4);

It will fill all array elements with 4.4

double[] d={2.3,4.5,5.6,7.8,9.8};
Arrays.fill(d,1,3,5.5);

Initializing Array using Arrays.setAll()

import java.util.Arrays;

public class MyClass {
    public static void main(String args[]) {
      double[] d=new double[5];
      Arrays.setAll(d,(index)-> index + 1.1);
      System.out.println(Arrays.toString(d));
      
    }
}

public class MyClass {

public static void main(String args[]) {

double[] d=new double[5];

Arrays.setAll(d,(index)-> index + 1.1);

System.out.println(Arrays.toString(d));

}

Enter the values for array
[1.1, 2.1, 3.1, 4.1, 5.1]

1 2	Enter the values for array [1.1, 2.1, 3.1, 4.1, 5.1]

DoubleStream to double Array in Java

DoubleStream is a sequence of double values that supports sequential and parallel aggregation operations.

DoubleStreams of() can be used to create a double stream of specified values.

toArray() of DoubleStream can use to convert it to an array.

import java.util.Arrays;
import java.util.stream.DoubleStream;
import java.util.Arrays;


public class MyClass {
    public static void main(String args[]) {
      DoubleStream ds=DoubleStream.of(7.5,66.7,88.7,333.4);
      double[] d=ds.toArray();
      System.out.println(Arrays.toString(d));
    }
}

import java.util.Arrays;

import java.util.stream.DoubleStream;

import java.util.Arrays;

public class MyClass {

public static void main(String args[]) {

DoubleStream ds=DoubleStream.of(7.5,66.7,88.7,333.4);

double[] d=ds.toArray();

System.out.println(Arrays.toString(d));

}

Enter the values for array
[7.5, 66.7, 88.7, 333.4]

1 2	Enter the values for array [7.5, 66.7, 88.7, 333.4]

double array Java length

The length of an array can be found using the length property.

public class MyClass {
    public static void main(String args[]) {
        double[] d={4.4,5.2,6.3,7.8};
        System.out.println("Array Length "+d.length);
    }
}

public class MyClass {

public static void main(String args[]) {

double[] d={4.4,5.2,6.3,7.8};

System.out.println("Array Length "+d.length);

}

Enter the values for array
Array Length 4

1 2	Enter the values for array Array Length 4

double to double array copy

To copy one array in to another we can use

clone()
System.arraycopy()
Arrays.copyOf()

there are other methods also we discuss above three here

double array copy using clone()

import java.util.Arrays;

public class MyClass {
    public static void main(String args[]) {
        double[] d={4.4,5.2,6.3,7.8};
       double[] e=d.clone();
       System.out.println(Arrays.toString(e));
    }
}

import java.util.Arrays;

public class MyClass {

public static void main(String args[]) {

double[] d={4.4,5.2,6.3,7.8};

double[] e=d.clone();

System.out.println(Arrays.toString(e));

}

array copy using System.arraycopy()

import java.util.Arrays;

public class MyClass {
    public static void main(String args[]) {
        double[] d={4.4,5.2,6.3,7.8};
       double[] e=new double[d.length];
       System.arraycopy(d,0,e,0,d.length);
       System.out.println(Arrays.toString(e));
    }
}

import java.util.Arrays;

public class MyClass {

public static void main(String args[]) {

double[] d={4.4,5.2,6.3,7.8};

double[] e=new double[d.length];

System.arraycopy(d,0,e,0,d.length);

System.out.println(Arrays.toString(e));

}

double array copy using Arrays.copyOf()

import java.util.Arrays;

public class MyClass {
    public static void main(String args[]) {
        double[] d={4.4,5.2,6.3,7.8};
       double[] e=Arrays.copyOf(d,d.length);
       System.out.println(Arrays.toString(e));
    }
}

import java.util.Arrays;

public class MyClass {

public static void main(String args[]) {

double[] d={4.4,5.2,6.3,7.8};

double[] e=Arrays.copyOf(d,d.length);

System.out.println(Arrays.toString(e));

}

Above all will copy double array d to e.

Enter the values for array
[4.4, 5.2, 6.3, 7.8]

1 2	Enter the values for array [4.4, 5.2, 6.3, 7.8]

Sorting double Array

Arrays class provides a method sort() to sort any type of array.

example to sort double array is as below.

import java.util.Arrays;

public class MyClass {
    public static void main(String args[]) {
        double[] d={6.6,5.5,7.8,1.1,2.1,4.3,7.1};
       Arrays.sort(d);
       System.out.println(Arrays.toString(d));
    }
}

import java.util.Arrays;

public class MyClass {

public static void main(String args[]) {

double[] d={6.6,5.5,7.8,1.1,2.1,4.3,7.1};

Arrays.sort(d);

System.out.println(Arrays.toString(d));

}

output of above program is here

[1.1, 2.1, 4.3, 5.5, 6.6, 7.1, 7.8]

1	[1.1, 2.1, 4.3, 5.5, 6.6, 7.1, 7.8]

There are different ways to sort and array we discussed only one.

One dimensional array in java with examples

What is One dimensional (Single dimensional) array in java

An array is a collection of similar elements. All array elements are stored in the contiguous memory location.

One dimensional or single dimensional array is an array with one dimension.

One dimensional array declaration in java

Syntax

    type arrayname[];
   Or type [] array name;<div class="open_grepper_editor" title="Edit &amp; Save To Grepper">

1 2	type arrayname[]; Or type [] array name;<div class="open_grepper_editor" title="Edit & Save To Grepper">

Example

int [] age;//collection of integer elements
float[] price;// collocation of float elements;
String [] names;// collocation of string element;<div class="open_grepper_editor" title="Edit &amp; Save To Grepper">

int [] age;//collection of integer elements

float[] price;// collocation of float elements;

String [] names;// collocation of string element;<div class="open_grepper_editor" title="Edit & Save To Grepper">

In above declaration age is a reference variable which will hold reference of array same for price and for names.

One dimensional array construction

Array uses new operator to dynamically allocating memory locations.
Syntax

    Array name= new type [size];

1	Array name= new type [size];

Example

age=new int[5];
price=new float[5];
names=new String[10];

age=new int[5];

price=new float[5];

names=new String[10];

new operator will dynamically allocate memory for 5 integer values that is 5*4=20 bytes continuously.

Array uses zero based indexing where first element is stored in zero location. Last element is stored in array size-1 location.

We can assign values in array element one by one as below

age[0]=21;
age[1]=43;
age[2]=34;
age[3]=37;
age[4]=55;

age[0]=21;

age[1]=43;

age[2]=34;

age[3]=37;

age[4]=55;

Single dimensional array initialization in java

Array declaration and initialization can be done in one statement
syntax

type[] array name = {value,value,…..value};

1	type[] array name = {value,value,…..value};

Example

int[] age= {21,43,34,37,55}

1	int[] age= {21,43,34,37,55}

Accessing array element: array element can be accessed by its index value.

Syntax

arrayName[indexExpression];

1	arrayName[indexExpression];

Example age[0] access all first value of array we can use loop
We can print all values is age below

One dimensional array in java examples

 public class MyClass {
    public static void main(String args[]) {
     double[]  price={22.33,44.22,55.66,33.66,77.11};
     for(int i=0;i<price.length;i++){
         System.out.println("price["+i+"]="+price[i]);
     }
    }
}

public class MyClass {

public static void main(String args[]) {

double[] price={22.33,44.22,55.66,33.66,77.11};

for(int i=0;i<price.length;i++){

System.out.println("price["+i+"]="+price[i]);

}

price[0]=22.33
price[1]=44.22
price[2]=55.66
price[3]=33.66
price[4]=77.11

price[0]=22.33

price[1]=44.22

price[2]=55.66

price[3]=33.66

price[4]=77.11

Array programs in java

public class FirstArray {

    public static void main(String[] s) {
        int[] age = new int[5];
        age[0] = 21;
        age[1] = 23;
        age[2] = 45;
        age[3] = 31;
        age[4] = 33;
        for (int i = 0; i < 5; i++) {
            System.out.println("age[" + i + "]= " + age[i]);
        }

    }
}

public class FirstArray {

public static void main(String[] s) {

int[] age = new int[5];

age[0] = 21;

age[1] = 23;

age[2] = 45;

age[3] = 31;

age[4] = 33;

for (int i = 0; i < 5; i++) {

System.out.println("age[" + i + "]= " + age[i]);

}

Result

age[0]= 21
age[1]= 23
age[2]= 45
age[3]= 31
age[4]= 33

age[0]= 21

age[1]= 23

age[2]= 45

age[3]= 31

age[4]= 33

We can also use for each loop to show array elements

Java array programs

public class JavaArray {

    public static void main(String[] s) {
        int[] age = new int[5];
        age[0] = 21;
        age[1] = 23;
        age[2] = 45;
        age[3] = 31;
        age[4] = 33;
        for (int a : age) {
            System.out.println("age= " + a);
        }

    }
}

public class JavaArray {

public static void main(String[] s) {

int[] age = new int[5];

age[0] = 21;

age[1] = 23;

age[2] = 45;

age[3] = 31;

age[4] = 33;

for (int a : age) {

System.out.println("age= " + a);

}

Output

age= 21
age= 23
age= 45
age= 31
age= 33

age= 21

age= 23

age= 45

age= 31

age= 33

Array input in java

Scanner class is used here to get Input in the array.

import java.util.Scanner;

public class ArrayInputByUser {

    public static void main(String[] args) {
        int[] age = new int[5];
        System.out.println("Enter  age to save in array");
        Scanner sc = new Scanner(System.in);
        for (int i = 0; i < 5; i++) {
            System.out.print("age[" + i + "]= ");
            age[i] = sc.nextInt();
        }
        System.out.println("Age array values are");
        for (int i = 0; i < 5; i++) {
            System.out.println("age[" + i + "]= " + age[i]);

        }
    }
}

import java.util.Scanner;

public class ArrayInputByUser {

public static void main(String[] args) {

int[] age = new int[5];

System.out.println("Enter age to save in array");

Scanner sc = new Scanner(System.in);

for (int i = 0; i < 5; i++) {

System.out.print("age[" + i + "]= ");

age[i] = sc.nextInt();

}

System.out.println("Age array values are");

for (int i = 0; i < 5; i++) {

System.out.println("age[" + i + "]= " + age[i]);

}

Enter  age to save in array
age[0]= 4
age[1]= 5
age[2]= 6
age[3]= 7
age[4]= 4
Age array values are
age[0]= 4
age[1]= 5
age[2]= 6
age[3]= 7
age[4]= 4

Enter age to save in array

age[0]= 4

age[1]= 5

age[2]= 6

age[3]= 7

age[4]= 4

Age array values are

age[0]= 4

age[1]= 5

age[2]= 6

age[3]= 7

age[4]= 4

Static array in java

To create an static array add keyword static before an array.

public class StaticArrayExample {

    static final String[] EMAILS = {"test@test.com", "one@test.com", "two@test.com"};

    public static void main(String[] args) {
        for (String s : EMAILS) {
            System.out.println(s);
        }

    }

}

public class StaticArrayExample {

static final String[] EMAILS = {"[email protected]", "[email protected]", "[email protected]"};

public static void main(String[] args) {

for (String s : EMAILS) {

System.out.println(s);

}

test@test.com
one@test.com
two@test.com

test@test.com

one@test.com

two@test.com

Length of array in java

length property of an array is used to find the length of an array

public class MyClass {
    public static void main(String args[]) {
     String[]  names={"Ram","Mohan","Sohan","Rita","Meeta","Geeta"};
           System.out.println("Total names are "+names.length );
     }
}

public class MyClass {

public static void main(String args[]) {

String[] names={"Ram","Mohan","Sohan","Rita","Meeta","Geeta"};

System.out.println("Total names are "+names.length );

}

Total names are 6

1	Total names are 6

How to store string in array in java

public class MyClass {
    public static void main(String args[]) {
        String[] names = {
            "Ram",
            "Mohan",
            "Sohan",
            "Rita",
            "Meeta",
            "Geeta"
        };

        System.out.println("Names are ");
        for (int i = 0; i < names.length; i++) {
            System.out.println(names[i]);
        }

        String[] branch = new String[5];
        branch[0] = "Computer Science & Engineering";
        branch[1] = "Mechanical Engineering";
        branch[2] = "Civil Engineering";
        branch[3] = "Electronics and Telecomm Engineering";
        branch[4] = "Information Technology";

        System.out.println("Branches are");
        for (String s: branch) {
            System.out.println(s);
        }
    }

}

public class MyClass {

public static void main(String args[]) {

String[] names = {

"Ram",

"Mohan",

"Sohan",

"Rita",

"Meeta",

"Geeta"

};

System.out.println("Names are ");

for (int i = 0; i < names.length; i++) {

System.out.println(names[i]);

}

String[] branch = new String[5];

branch[0] = "Computer Science & Engineering";

branch[1] = "Mechanical Engineering";

branch[2] = "Civil Engineering";

branch[3] = "Electronics and Telecomm Engineering";

branch[4] = "Information Technology";

System.out.println("Branches are");

for (String s: branch) {

System.out.println(s);

}

Names are 
Ram
Mohan
Sohan
Rita
Meeta
Geeta
Branches are
Computer Science & Engineering
Mechanical Engineering
Civil Engineering
Electronics and Telecomm Engineering
Information Technology

Names are

Ram

Mohan

Sohan

Rita

Meeta

Geeta

Branches are

Computer Science & Engineering

Mechanical Engineering

Civil Engineering

Electronics and Telecomm Engineering

Information Technology

String to integer array in java

public class StringtoIntArray {

    public static void main(String[] args) {
        String s1 = "[1,2,3,4,5,6,7,8,9]";
        System.out.println("String is "+s1);
        StringTokenizer s2 = new StringTokenizer(s1, "[,] ");
        int length = s2.countTokens();
        int[] intArray = new int[length];
        int i=0;
        while (s2.hasMoreTokens()) {
            intArray[i]=Integer.parseInt(s2.nextToken());
            i++;
        }
        System.out.println("Integer Array is ");
        for (int j = 0; j < intArray.length; j++) {
            System.out.println("intArray["+j+"] = "+intArray[j]);
            
        }
    }
}

public class StringtoIntArray {

public static void main(String[] args) {

String s1 = "[1,2,3,4,5,6,7,8,9]";

System.out.println("String is "+s1);

StringTokenizer s2 = new StringTokenizer(s1, "[,] ");

int length = s2.countTokens();

int[] intArray = new int[length];

int i=0;

while (s2.hasMoreTokens()) {

intArray[i]=Integer.parseInt(s2.nextToken());

i++;

}

System.out.println("Integer Array is ");

for (int j = 0; j < intArray.length; j++) {

System.out.println("intArray["+j+"] = "+intArray[j]);

}

This program is taking a string as an argument converting it to StringTokenizer based on delimiter [,] and space.

String tokenizer contains a set of string tokens these tokens are converted to an integer using Integer.parseInt().

above program can handle the following strings

String s1 = “1 2 3 4 5 6 7 8 9”; or

String s1 = “1,2,3,4,5,6,7,8,9”;

String s1 = “[1,2,3,4,5,6,7,8,9]”;

String is [1,2,3,4,5,6,7,8,9]
Integer Array is 
intArray[0] = 1
intArray[1] = 2
intArray[2] = 3
intArray[3] = 4
intArray[4] = 5
intArray[5] = 6
intArray[6] = 7
intArray[7] = 8
intArray[8] = 9

String is [1,2,3,4,5,6,7,8,9]

Integer Array is

intArray[0] = 1

intArray[1] = 2

intArray[2] = 3

intArray[3] = 4

intArray[4] = 5

intArray[5] = 6

intArray[6] = 7

intArray[7] = 8

intArray[8] = 9

Anonymous array in java

anonymous array in java are arrays without name

new Integer[]{1, 2, 3, 4, 5, 6, 7}

new String[]{“Ram”,”Mohan”,”Sohan”};

public class AnonymousArray {

    public static void printArray(Integer[] arr) {
        for (Integer a : arr) {
            System.out.print(" "+a);
        }
    }

    public static void main(String[] args) {
        AnonymousArray.printArray(new Integer[]{1, 2, 3, 4, 5, 6, 7});
       
    }

}

public class AnonymousArray {

public static void printArray(Integer[] arr) {

for (Integer a : arr) {

System.out.print(" "+a);

}

public static void main(String[] args) {

AnonymousArray.printArray(new Integer[]{1, 2, 3, 4, 5, 6, 7});

}

How to get the length of the 2D array in Java

Two dimensional array in java

To declare an 2D array in java we use the following syntax

Datatype [][] arrayName=new Datatype[rows][cols]

If you want to declare any primitive 2D array.

int [][] ages=new int[3][4];

double [][] prices=new double[4][4]

Array ages is a two-dimensional int array, it can store 3 rows and each row can contain 4 values (columns) total of 3*4=12 values.

similar price is a two-dimensional double array, it can store 4 rows and 4 columns total (4*4) 20 elements.

Two-dimensional array initialization

int[][] ages = {
            {1, 2, 3},
            {4, 5, 6},
            {7, 8, 9}
        };

        int[][] b = new int[2][2];
        b[0][0] = 1;
        b[0][1] = 2;
        b[1][0] = 3;
        b[1][1] = 4;

int[][] ages = {

{1, 2, 3},

{4, 5, 6},

{7, 8, 9}

};

int[][] b = new int[2][2];

b[0][0] = 1;

b[0][1] = 2;

b[1][0] = 3;

b[1][1] = 4;

above are the two-dimension array declared and initialized.

Length of an array in Java

Java array provides a variable length to find the length of a variable.4

to find the length of one dimension array we use following code

        int[] a={1,2,3,4,5,6};
        int length=a.length;
        System.out.println("Length of an array is "+length);

int[] a={1,2,3,4,5,6};

int length=a.length;

System.out.println("Length of an array is "+length);

One dimension array length is number of elements in array

Length of the 2D array in Java

In a two-dimensional array, java length is the number of rows in 2D array.

   public class ArrayEx {

    public static void main(String[] args) {

        int[][] ages = {
            {1, 2, 3},
            {4, 5, 6},
            {7, 8, 9}
        };

        int[][] b = new int[2][2];
        b[0][0] = 1;
        b[0][1] = 2;
        b[1][0] = 3;
        b[1][1] = 4;

        double[][] prices = {
            {12.33, 44.20, 54.06, 41.54, 32.44},
            {12.33},
            {},
            {32.22, 43.24, 54.22},
            {44.44, 53.43, 23.12}
        };
        System.out.println("Length of ages " + ages.length);
        System.out.println("Length of b " + b.length);
        System.out.println("Length of prices " + prices.length);

    }

}

public class ArrayEx {

public static void main(String[] args) {

int[][] ages = {

{1, 2, 3},

{4, 5, 6},

{7, 8, 9}

};

int[][] b = new int[2][2];

b[0][0] = 1;

b[0][1] = 2;

b[1][0] = 3;

b[1][1] = 4;

double[][] prices = {

{12.33, 44.20, 54.06, 41.54, 32.44},

{12.33},

{},

{32.22, 43.24, 54.22},

{44.44, 53.43, 23.12}

};

System.out.println("Length of ages " + ages.length);

System.out.println("Length of b " + b.length);

System.out.println("Length of prices " + prices.length);

}

Length of ages 3
Length of b 2
Length of prices 5

Length of ages 3

Length of b 2

Length of prices 5

To access each row length we can use the following code

   System.out.println("Length of ages[0] " + ages[0].length);
        System.out.println("Length of ages[1] " + ages[1].length);
        System.out.println("Length of ages[2] " + ages[2].length);
        System.out.println("Length of b[0] " + b[0].length);
        System.out.println("Length of b[1] " + b[1].length);
        System.out.println("Length of prices[0] " + prices[0].length);
        System.out.println("Length of prices[1] " + prices[1].length);
        System.out.println("Length of prices[2] " + prices[2].length);
        System.out.println("Length of prices[3] " + prices[3].length);
        System.out.println("Length of prices[4] " + prices[4].length);

System.out.println("Length of ages[0] " + ages[0].length);

System.out.println("Length of ages[1] " + ages[1].length);

System.out.println("Length of ages[2] " + ages[2].length);

System.out.println("Length of b[0] " + b[0].length);

System.out.println("Length of b[1] " + b[1].length);

System.out.println("Length of prices[0] " + prices[0].length);

System.out.println("Length of prices[1] " + prices[1].length);

System.out.println("Length of prices[2] " + prices[2].length);

System.out.println("Length of prices[3] " + prices[3].length);

System.out.println("Length of prices[4] " + prices[4].length);

Length of ages[0] 3
Length of ages[1] 3
Length of ages[2] 3
Length of b[0] 2
Length of b[1] 2
Length of prices[0] 5
Length of prices[1] 1
Length of prices[2] 0
Length of prices[3] 3
Length of prices[4] 3

Length of ages[0] 3

Length of ages[1] 3

Length of ages[2] 3

Length of b[0] 2

Length of b[1] 2

Length of prices[0] 5

Length of prices[1] 1

Length of prices[2] 0

Length of prices[3] 3

Length of prices[4] 3

Exception Handling try catch finally blocks in Java

What is try block

A try block is used to surround a set of statements where exceptions may occur.

A try block used with catch and finally block

What is a catch block

A catch block is created followed by a try block.

Whenever an exception is thrown from try block it catches in the appropriate catch block

There can be more than one catch block for a try block.

Syntax of try catch block

try{
        //statements to check for exception
   }catch(ExceptionType e){
      //statments to handle exception
   }

try{

//statements to check for exception

}catch(ExceptionType e){

//statments to handle exception

}

Java finally block

Java finally block is also associated with a try block.

Finally block is used to release resources that are used in a try block.

like closing a file. closing database connection

Finally block gets always executed when there is exception or not in try block.

We can use try and finally or try catch and finally.

Syntax of try-catch and finally

1 try and finally

try{
        //statements to check for exception
   }finally{
      //statments to release resource
   }

try{

//statements to check for exception

}finally{

//statments to release resource

}

2 try catch and finally

try{
        //statements to check for exception
   }catch(ExceptionType e){
      //statments to handle exception
   }finally{
      //statments to release resource
   }

try{

//statements to check for exception

}catch(ExceptionType e){

//statments to handle exception

}finally{

//statments to release resource

}

try catch java examples

ArithmeticException Example in Java

class ExceptionHandling1 {

    public static void main(String args[]) {
        int d, a;

        try { 	// monitor a block of code for exception.
            d = 0;
            a = 42 / d;
            System.out.println("This will not be printed.");
        } catch (ArithmeticException e) { // catch divide-by-zero error				
            System.out.println("Division by zero." + e);
        }
        System.out.println("After catch block.");
    }
}

class ExceptionHandling1 {

public static void main(String args[]) {

int d, a;

try { // monitor a block of code for exception.

d = 0;

a = 42 / d;

System.out.println("This will not be printed.");

} catch (ArithmeticException e) { // catch divide-by-zero error

System.out.println("Division by zero." + e);

}

System.out.println("After catch block.");

}

Output

Division by zero.java.lang.ArithmeticException: / by zero
After catch block.

1 2	Division by zero.java.lang.ArithmeticException: / by zero After catch block.

Exception occurs at the line “a = 42 / d; “ , then this exception is thrown, program control transfer from try block to catch block.

Once catch block has executed program control continue with the next line in a program following entire try/catch statement.

In the line “catch (ArithmeticException e) “ e is a reference of exception “ArithmeticException”.

When we print the value of “e “ it will print ( java.lang.ArithmeticException:/by zero at Test.main(Test.java:6) )

ArithmeticException is an exception class which resides in java.lang package.
“/by zero” is a type of arithmetic exception (divided by zero).
“Test” is the name of the class.
“main” is a method in which an exception occurs.
6 is line number in which exception occured.

Java try catch multiple exceptions

1 Try and multiple catch blocks

In java programming, when within a try block multiple exceptions occur then for handling those multiple exceptions we use multiple catches with a single try block.

class MultiCatchDemo {

    public static void main(String args[]) {
        try {
            int a = args.length;
            System.out.println("a = " + a);
            int b = 42 / a;
            int c[] = {1};
            c[42] = 99;
        } catch (ArithmeticException e) {
            System.out.println("You can not divide a number by zero: " + e);
        } catch (ArrayIndexOutOfBoundsException exc) {
            System.out.println("Array index out of bounds exception: " + exc);
        }
        System.out.println("After try catch blocks.");
    }
}

class MultiCatchDemo {

public static void main(String args[]) {

try {

int a = args.length;

System.out.println("a = " + a);

int b = 42 / a;

int c[] = {1};

c[42] = 99;

} catch (ArithmeticException e) {

System.out.println("You can not divide a number by zero: " + e);

} catch (ArrayIndexOutOfBoundsException exc) {

System.out.println("Array index out of bounds exception: " + exc);

}

System.out.println("After try catch blocks.");

}

When we pass no command line argument (during run time) than the length of command line argument (args.length) is zero means value of variable “a” is 0.

Than the output is:

 Output: c:\> Java  MultiCatch
 a = 0
 Divided By zero:java: java.lang.ArithmeticException:/by zero  				
 After try/catch

Output: c:\> Java MultiCatch

a = 0

Divided By zero:java: java.lang.ArithmeticException:/by zero

After try/catch

When we pass one or more command line argument ( in this program one command line argument is passed “test” during run time) than the length of command line argument (args.length) is one means value of variable “a” is 1.

Than the output is:

C:\> Java  MultiCatch test
a = 1											
Array index out of bounds exception: java.lang.ArrayIndexOutOfBoundException:42 
After try catch

C:\> Java MultiCatch test

a = 1

Array index out of bounds exception: java.lang.ArrayIndexOutOfBoundException:42

After try catch

2 Java try catch multiple exceptions

public class MultiCatchDemo {

    public static void main(String args[]) {
        try {
            int a = args.length;
            System.out.println("a = " + a);
            int b = 42 / a;
            int c[] = {1};
            c[42] = 99;
        } catch (ArithmeticException| ArrayIndexOutOfBoundsException e) {
            System.out.println("Exception: " + e);
        }
        System.out.println("After try catch blocks.");
    }
}

public class MultiCatchDemo {

public static void main(String args[]) {

try {

int a = args.length;

System.out.println("a = " + a);

int b = 42 / a;

int c[] = {1};

c[42] = 99;

} catch (ArithmeticException| ArrayIndexOutOfBoundsException e) {

System.out.println("Exception: " + e);

}

System.out.println("After try catch blocks.");

}

Unreachable Code in Exception Handling

In Java programming, in a sequence of catch statement exception subclass must come before its super class.

In a series, if exception super class comes before its subclass than exception sub class would never be reached.

It is known as unreachable code. In Java programming, unreachable code is an compile-time error.

Example unreachable code in Exception Handling

class SuperSubCatch {

    public static void main(String args[]) {
        try {
            int a = 0;
            int b = 55 / a;// divided by zero ArithmeticException
        } catch (Exception e) {
            System.out.println("Exception ");
        } /* This catch is never executed because  General class Exception is before then  specific class ArithmeticException. */ 
        catch (ArithmeticException e) {// ERROR - unreachable			{ 

            System.out.println("This is never reached.");
        }
    }
}

class SuperSubCatch {

public static void main(String args[]) {

try {

int a = 0;

int b = 55 / a;// divided by zero ArithmeticException

} catch (Exception e) {

System.out.println("Exception ");

} /* This catch is never executed because General class Exception is before then specific class ArithmeticException. */

catch (ArithmeticException e) {// ERROR - unreachable {

System.out.println("This is never reached.");

}

If we will try to compile this program we will receive an error message stating that the second catch statement is unreachable because ArithmeticException is a subclass of the Exception class.

Then the first catch statement will handle all exception-based errors, including Arithmetic Exception therefore second catch statement will never execute.

To solve the problem, reverse the order of the catch statement.

Nested try catch Java statements

In java programming, it is possible to create a try block within another try block. Such try block is known as nested try.

Nested try catch Example

class TryNest {

    public static void main(String args[]) {
        try {
            int a = args.length;

            /* If args.length is zero then the following statement
               will generate a divide-by-zero ArithmeticException. */
            int b = 55 / a;
            System.out.println("a = " + a);

            try { // nested try block
                /* If one command line arg is used, then an Array index out-of-bounds
                     exception will be generated by the following code. */

                if (a == 1) {
                    int c[] = {1};
                    c[42] = 99; // generate an out-of-bounds exception
                }
            } catch (ArrayIndexOutOfBoundsException e) {
                System.out.println("Array index out-of-bounds: " + e);
            }

        } catch (ArithmeticException e) {
            System.out.println("You can not divide a number by zero  " + e);
        }
    }
}

class TryNest {

public static void main(String args[]) {

try {

int a = args.length;

/* If args.length is zero then the following statement

will generate a divide-by-zero ArithmeticException. */

int b = 55 / a;

System.out.println("a = " + a);

try { // nested try block

/* If one command line arg is used, then an Array index out-of-bounds

exception will be generated by the following code. */

if (a == 1) {

int c[] = {1};

c[42] = 99; // generate an out-of-bounds exception

}

} catch (ArrayIndexOutOfBoundsException e) {

System.out.println("Array index out-of-bounds: " + e);

}

} catch (ArithmeticException e) {

System.out.println("You can not divide a number by zero " + e);

}

If there is no command line argument present then the output.

c:> Java  NestTry	
a = 0							
Divided By zero:java: java.lang.ArithmeticException:/by zero 
After try/catch

c:> Java NestTry

a = 0

Divided By zero:java: java.lang.ArithmeticException:/by zero

After try/catch

If there is no command line argument present then the output.

c:> Java  NestTry one 
a = 1	
Array index out-of-bounds: java.lang.ArrayIndexOutOfBoundException:42 
After try/catch

c:> Java NestTry one

a = 1

Array index out-of-bounds: java.lang.ArrayIndexOutOfBoundException:42

After try/catch

User-Defined Exception in Java with Examples

Q : When a statement within a try block causes an exception, the remaining statements in the try block

Ans: Will Not be executed

Q: In a try/catch construct, after the catch statement is executed:

Ans: Statement just after the catch is executed

Q: Can you have multiple catch blocks on a try statement

Ans: Yes, as per the need we can have multiple catch blocks on a try statement

Q: To catch an exception, the code that might throw the exception must be enclosed in a ____________

Ans: try block

Q: If an exception occurs in a try-catch block, the code in the finally clause ________.

Ans: Get Executed. If with try block finally is associated then it always gets executed no matter it throws an exception or not.

Q: A try block may be followed by a finally block, without a catch block (Java try without catch).

Ans: Yes we can use try and finally without a catch block.

Q: Exceptions can be thrown by ________.

Ans: Throw statement is used to throw an Exception

Q: When is the code within a catch block executed?

Ans: If an exception occurs within the code in the try block then matched exception in the catch block gets executed.

Java unreported exception How to Handle it

The unreported exception is due to you have checked exception in your program and you are not handling it.

You can handle it

By using try catch block
By using throws keyword in method

unreported exception

Which of the following Throwables needs to be declared?

Error
RuntimeException
CheckedException
Exception

Answer is 3

More MCQ

Throw and Throws Keywords in Java

In java programming, If the exception occurs within the try block it is thrown.

a throw keyword is used to throw an exception

A system-generated exception is automatically thrown by the java run time system but if we want to manually throw an exception, we can do so by using the throw keyword.

Exception Handling try catch finally blocks in Java

Syntax of throw

throw ThrowableInstance;

here, ThrowableInstance must be an object of type Throwable or subclass of Throwable.

Example of throw keyword

class DemoThrow {
    void demo() {
        try {
            throw new NullPointerException("demo"); //demo is a name of exception
        } catch (NullPointerException e) {
            System.out.println("Inside demo's catch");
            throw e; // re-throw the exception
        }
    }
}
public class TestDemo {
    public static void main(String args[]) {
        DemoThrow ob = new DemoThrow();
        try {
            ob.demo();
        } catch (NullPointerException e) {
            System.out.println("Recaught: " + e);
        }
    }
}

class DemoThrow {

void demo() {

try {

throw new NullPointerException("demo"); //demo is a name of exception

} catch (NullPointerException e) {

System.out.println("Inside demo's catch");

throw e; // re-throw the exception

}

public class TestDemo {

public static void main(String args[]) {

DemoThrow ob = new DemoThrow();

try {

ob.demo();

} catch (NullPointerException e) {

System.out.println("Recaught: " + e);

}

Inside demo's catch
Recaught: java.lang.NullPointerException: demo

1 2	Inside demo's catch Recaught: java.lang.NullPointerException: demo

In this program new is used to create an instance of NullPointerException and we get two chance to deal with the same error.

In the line “throw new NullPointerException(“demo”);”

throw keyword is used to throw NullPointerException(“demo”). Here we set “demo” is a name of exception.

This NullPointerException(“demo”) catch by catch() method which resides in a demo() method.

Line “throw e;” re-throw the exception which is catch by catch() method which resides in a main() method.

Throws Keyword in Java

In a java programming, throws keyword list the type of exception that a method might throw.

throws keyword inform that method throws mentioned exceptions

In the throws clause, we declare all the exceptions that a method can throw.

Syntax of throws:

type  method_name(parameter list) throws exception1, exception2 ….{		
}

1 2	type method_name(parameter list) throws exception1, exception2 ….{ }

Here, exception1, exception2 are comma, list of the exception that a method can throw.

Example of throws

class ExceptionClass {
    void demo() throws NullPointerException { // define throws
        System.out.println("Inside demo method.");
        throw new NullPointerException("demo");
    }
}
public class ExceptionMain {
    public static void main(String args[]) {
        ExceptionClass ob = new ExceptionClass();
        try {
            ob.demo(); // demo() definition comes within try block
        } catch (NullPointerException e) {
            System.out.println("Caught " + e);
        }
    }
}

class ExceptionClass {

void demo() throws NullPointerException { // define throws

System.out.println("Inside demo method.");

throw new NullPointerException("demo");

}

public class ExceptionMain {

public static void main(String args[]) {

ExceptionClass ob = new ExceptionClass();

try {

ob.demo(); // demo() definition comes within try block

} catch (NullPointerException e) {

System.out.println("Caught " + e);

}

Inside demo method.
Caught java.lang.NullPointerException: demo

1 2	Inside demo method. Caught java.lang.NullPointerException: demo

Explaination: We throws NullPointerException in the line “throw new NullPointerException(“demo”);” .

Here we set “demo” is a name of thread.

This line “throw new NullPointerException(“demo”);” throw the exception which is handled by catch block associated with try within main().

Difference between throw and throws in Java (throw vs throws)

throw keyword is used to throw an exception from method or from a block

throw is used inside method

throw new NullPointerException("demo");

throws keyword is used to inform that a method throws exception(s)

thorws keyword i s used in method header

public Scanner(File source) throws FileNotFoundException

What is the purpose of the throw statement?

Throw is used to throw an exception from a method or from block of code

what is the difference between throwing an exception and catching an exception?

Throwing an exception can use to throw an exception using the throw keyword.

this can be implicit or explicit

45/0 <- throw ArithmeticException

throw ArithmeticException(“Denominator can not be zero”);

To catch an exception one or more catch blocks can be used so that program executes properly.

The ______ keyword is used to manually throw an exception in java

The Throw keyword is used to manually throw an exception.

Reference

How to Throw Exceptions

User Defined (Custom) Exceptions in Java with Examples

In Java programming, it is possible to create our own exception and such exception are called user defined exception in Java.

Exception class is a predefined class. Any user defined exception created by us must be a subclass of the predefine Exception class and created by extending the Exception class.

What is user defined (custom) exception in java

An Exception that is defined by the user/ programmer is known as user defined or custom exception.

example

Checking user age if not valid age throw an exception
If not in a specified time period then throw an exception
If the user name and password is incorrect then throw an exception

All above exceptions are created by the user and throw when required.

How to throw user defined exception in java

The throw and throws keyword are used for implementing user defined exception.

throw: throw keyword is used to throw an exception explicitly from a method or from a block.

for instance

 throw new NumberIsGreaterException();

1	throw new NumberIsGreaterException();

Here new NumberIsGreaterException();

is creating new exception and throwing it.

throws: throws keyword is used with method signature that informs that the method can throw mentioned exception.

public Scanner(File source)
        throws FileNotFoundException

1 2	public Scanner(File source) throws FileNotFoundException

Here Scanner is class and above mentioned Scanner represents the constructor call, On the constructor call of above we have to handle File not found Exception.

how to create user defined exception in java

Create a class
Extend the Exception class
Create a String argument constructor to pass custom message.

public class Exception1 extends exception{
      Exception1(String msg){
         super(msg);
         //or print message   
}

public class Exception1 extends exception{

Exception1(String msg){

super(msg);

//or print message

}

Examples of User Defined Exception in Java

Example1: write a program to take a number from user by using command line argument during run time. if user will enter more than 100 then grnerate user defined exception MyException.

class NumberIsGreaterException extends Exception {
    NumberIsGreaterException() {
        System.out.println("User Exception ");
    }
}
public class TestMain {
    public static void main(String args[]) {
        try {
            int m = Integer.parseInt(args[0]);
            if (m > 100) {
                throw new NumberIsGreaterException();
            }
        } catch (NumberIsGreaterException e) {
            System.out.println(e);
        }
        System.out.println("After try, and catch ");
    }
}

class NumberIsGreaterException extends Exception {

NumberIsGreaterException() {

System.out.println("User Exception ");

}

public class TestMain {

public static void main(String args[]) {

try {

int m = Integer.parseInt(args[0]);

if (m > 100) {

throw new NumberIsGreaterException();

}

} catch (NumberIsGreaterException e) {

System.out.println(e);

}

System.out.println("After try, and catch ");

}

java TestMain 111
User Exception 
NumberIsGreaterException
After try, and catch

java TestMain 111

User Exception

NumberIsGreaterException

After try, and catch

Explaination: In the above program, name of user define exception is NumberIsGreaterException.

In the above program user enter the number 111 during run time using command line argument.

Here value of “m” is greter than 100 therefore “throw newNumberIsGreaterException ();” this throw statement throw the exception and catch by catch block, but before thorw “NumberIsGreaterException ()” constructer will call.

User defined exception in java program to check age is valid or not

InvalidAgeException.java

class InvalidAgeException extends Exception {
    InvalidAgeException(String s) {
        super(s);
    }
}

class InvalidAgeException extends Exception {

InvalidAgeException(String s) {

super(s);

}

CheckAge.java

import java.util.Scanner;
public class CheckAge {

    void validateAge(int age) throws InvalidAgeException {
        if (age <= 100 && age > 0) {
            System.out.println("Valid age");
        } else {
            throw new InvalidAgeException("Age is not valid");
        }
    }

    public static void main(String[] s) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter your age");
        int age = sc.nextInt();
        CheckAge ck = new CheckAge();
        try {
            ck.validateAge(age);
        } catch (InvalidAgeException e) {
            System.out.println("Invalid Age " + e.getMessage());
        }
    }
}

import java.util.Scanner;

public class CheckAge {

void validateAge(int age) throws InvalidAgeException {

if (age <= 100 && age > 0) {

System.out.println("Valid age");

} else {

throw new InvalidAgeException("Age is not valid");

}

public static void main(String[] s) {

Scanner sc = new Scanner(System.in);

System.out.println("Enter your age");

int age = sc.nextInt();

CheckAge ck = new CheckAge();

try {

ck.validateAge(age);

} catch (InvalidAgeException e) {

System.out.println("Invalid Age " + e.getMessage());

}

Output

D:\Test Java>javac CheckAge.java 
D:\Test Java>java CheckAge
Enter your age
23
Valid age
D:\Test Java>java CheckAge
Enter your age
112
InvalidAgeException: Age is not valid
        at CheckAge.validateAge(CheckAge.java:9)
        at CheckAge.main(CheckAge.java:19)

D:\Test Java>javac CheckAge.java

D:\Test Java>java CheckAge

Enter your age

Valid age

D:\Test Java>java CheckAge

Enter your age

112

InvalidAgeException: Age is not valid

at CheckAge.validateAge(CheckAge.java:9)

at CheckAge.main(CheckAge.java:19)

user defined exception in java example to check a time is in range or not, if time is not in range then throw custom exception

InvalidTimeException.java

class InvalidTimeException extends Exception {
    InvalidTimeException(String s) {
        super(s);
    }
}

class InvalidTimeException extends Exception {

InvalidTimeException(String s) {

super(s);

}

CheckTime.java

import java.text.SimpleDateFormat;
import java.util.Date;
import java.text.ParseException;
public class CheckTime {

    void validateTime(String time) throws InvalidTimeException, ParseException {
        String from = "08:12:00";
        String to = "11:12:00";

        Date date_from = null;
        Date date_to = null;
        Date dateNow = null;
        SimpleDateFormat formatter = new SimpleDateFormat("HH:mm:ss");
        date_from = formatter.parse(from);
        date_to = formatter.parse(to);
        dateNow = formatter.parse(time);


        if (date_from.before(dateNow) && date_to.after(dateNow)) {
            System.out.println("Valid Time");
        } else {
            throw new InvalidTimeException("Time is not in range");
        }
    }

    public static void main(String[] s) {
        String n = "09:10:00";
        CheckTime ck = new CheckTime();
        try {
            ck.validateTime(n);
        } catch (InvalidTimeException e) {
            System.out.println("Invalid Time " + e);
        } catch (ParseException e) {
            System.out.println("ParseException " + e);
        }

    }
}

import java.text.SimpleDateFormat;

import java.util.Date;

import java.text.ParseException;

public class CheckTime {

void validateTime(String time) throws InvalidTimeException, ParseException {

String from = "08:12:00";

String to = "11:12:00";

Date date_from = null;

Date date_to = null;

Date dateNow = null;

SimpleDateFormat formatter = new SimpleDateFormat("HH:mm:ss");

date_from = formatter.parse(from);

date_to = formatter.parse(to);

dateNow = formatter.parse(time);

if (date_from.before(dateNow) && date_to.after(dateNow)) {

System.out.println("Valid Time");

} else {

throw new InvalidTimeException("Time is not in range");

}

public static void main(String[] s) {

String n = "09:10:00";

CheckTime ck = new CheckTime();

try {

ck.validateTime(n);

} catch (InvalidTimeException e) {

System.out.println("Invalid Time " + e);

} catch (ParseException e) {

System.out.println("ParseException " + e);

}

Output

D:\Test Java>java CheckTime
Valid Time

1 2	D:\Test Java>java CheckTime Valid Time

Example: Write a program to create user defined exception in Java to check a given name exists or not. If name doesn’t exists then throw a custom exception.

InvalidNameException.java

class InvalidNameException extends Exception {
    InvalidNameException(String s) {
        super(s);
    }
}

class InvalidNameException extends Exception {

InvalidNameException(String s) {

super(s);

}

CheckName.java

import java.util.Scanner;
public class CheckName {

    void validateName(String name) throws InvalidNameException {

        String[] names = {
            "Ram",
            "Mohan",
            "Sohan",
            "Mita",
            "Neeta",
            "Anita"
        };
        boolean found = false;
        for (String n: names) {
            if (n.equalsIgnoreCase(name)) {
                found = true;
                break;
            }
        }
        if (found) {
            System.out.println("Valid Name");
        } else {
            throw new InvalidNameException("Not a valid name");
        }

    }


    public static void main(String[] s) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter Name");
        String name = sc.next();
        CheckName ck = new CheckName();
        try {
            ck.validateName(name);
        } catch (InvalidNameException e) {
            System.out.println("Invalid Name " + e);
        }
    }
}

import java.util.Scanner;

public class CheckName {

void validateName(String name) throws InvalidNameException {

String[] names = {

"Ram",

"Mohan",

"Sohan",

"Mita",

"Neeta",

"Anita"

};

boolean found = false;

for (String n: names) {

if (n.equalsIgnoreCase(name)) {

found = true;

break;

}

if (found) {

System.out.println("Valid Name");

} else {

throw new InvalidNameException("Not a valid name");

}

public static void main(String[] s) {

Scanner sc = new Scanner(System.in);

System.out.println("Enter Name");

String name = sc.next();

CheckName ck = new CheckName();

try {

ck.validateName(name);

} catch (InvalidNameException e) {

System.out.println("Invalid Name " + e);

}

Output

D:\Test Java>javac CheckName.java
D:\Test Java>java CheckName
Enter Name
Manish
Invalid Name InvalidNameException: Not a valid name
D:\Test Java>java CheckName
Enter Name
Ram
Valid Name

D:\Test Java>javac CheckName.java

D:\Test Java>java CheckName

Enter Name

Manish

Invalid Name InvalidNameException: Not a valid name

D:\Test Java>java CheckName

Enter Name

Ram

Valid Name

How to write custom exception in java?

How to create custom exception in java?

How to create your own exception in java?

Create a class
Extend Exception class
Create a constructor to show/pass custom message

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