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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.

User Defined Exception in Java with Examples

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

Thread Life Cycle in Java

Thread Life Cycle in Java tells the various information of thread form born to terminate.

Thread life cycle contains the several stages and at a time any thread can be present in a single state.

States of Thread life cycle

Born
Ready
Running
Blocked
Sleep
Wait
Dead

Ready: In this state thread is ready to execute but not running.

When the start() method calls thread enters from born to ready state.

Running: When a run() method executes highest priority ready thread assigned a processor and enter in a running state for execution.

Thread can visit more than ones in a running state.

Blocked: When a running thread has a input-output issue it enters in a blocked state from running state and when input-output issue solves it again comes in a running thread.

Sleep : A running thread enter in a sleep state for a specified number of milliseconds when a sleep() method calls.

When sleep time expires then thread moves to ready state.

Wait : When a low priority thread executing and high priority thread comes then high priority thread get preference and enter in a running state. Then low priority thread leaves a running state and moves to wait state for indefinite time.

When a high priority thread execution completes it calls waiting thread for execution by notify () & notifyall () method.

Dead: A running thread is enter in a dead state when its execution completes (run() method completes) or terminate for any reason.

Multithreading in java example programs

Created a class Thread1 that extends Thread class
main() creates two thread t1 and t2.
To start thread start method is called t1.start() and t2.start()
Start method calls the run method to execute the work
Thread.sleep() send thread to sleep state for 500 milliseconds
From sleep state thread come back to ready then running state
After completing work thread get dead.

class Thread1 extends Thread {

    public void run() {
        try {
            for (int i = 1; i <= 5; i++) {
                System.out.println("Running Thread: " + i);
                Thread.sleep(500);
            }
        } catch (InterruptedException e) {
            System.out.println("InterruptedException ");
        }
    }
}

public class TreadExample {

    public static void main(String[] args) {

        Thread1 t1 = new Thread1();
        t1.start();
        Thread1 t2 = new Thread1();
        t2.start();

    }

}

class Thread1 extends Thread {

public void run() {

try {

for (int i = 1; i <= 5; i++) {

System.out.println("Running Thread: " + i);

Thread.sleep(500);

}

} catch (InterruptedException e) {

System.out.println("InterruptedException ");

}

public class TreadExample {

public static void main(String[] args) {

Thread1 t1 = new Thread1();

t1.start();

Thread1 t2 = new Thread1();

t2.start();

}

Running Thread: 1
Running Thread: 1
Running Thread: 2
Running Thread: 2
Running Thread: 3
Running Thread: 3
Running Thread: 4
Running Thread: 4
Running Thread: 5
Running Thread: 5

Running Thread: 1

Running Thread: 2

Running Thread: 3

Running Thread: 4

Running Thread: 5

Multithreading in Java

Multithreading in Java Thread Creation Method Use Example

1 What is a Thread in Java

A thread is light weight process that can execute simultaneously. Multithreading in java allows multiple threads to run simultaneously.

A program can be divided into two or more parts that can run concurrently and each part of such program is known as thread.
In a simple word, thread is a lightweight sub-process.
It is a smallest unit of processing.
When these threads execute concurrently for accomplishing a task is known multithreading.
In multithreading, each thread defines a separate path of execution.
In multithreading, every thread has a priority between 1 to 10. Thread with highest priority get preference over lower priority thread for execution.

In a java programming, Thread is a predefined class within a java.lang package.

Operating system (OS) can contain multiple process, in the above figure, there are three process P1,P2 & P3, within OS and within P3 process there are three threads T1, T2& T3. There is context-switching between the threads.

2 Difference between Process and Thread

Process	Thread
A process has their own virtual address space.	Threads are entities within a process it uses its virtual address space of process.
Two processes running on the same system at the same time do not uses address space.	Two threads running within a process uses the same address space.
Every process has its own data segment	All threads within the process uses the same data segment of process.
In multiprocessing, processes use inter process communication techniques to interact with other processes.	In multithreading, threads do not uses inter process communication techniques because they not uses separate address spaces. They share the same address space therefore, they can communicate directly with other threads within process.
Processes have considerable overhead.	Threads have almost no overhead;
Process is heavy weight.	Threads are light weight process (LWP).
Process contains much information about system, resource.	Threads carry less state information than process
When we create a child process from a parent process then it requires duplication of the resources of parent process.	No duplication of resources is required when we create a child thread from main thread.

3 How to create a thread in Java

We can create a thread by two ways:

By extending Thread
By implementing Runnable interface

Lets see multithreading in java with example

A Creating Thread By Implementing Runnable Interface

We can create a thread by creating a class that implements the Runnable interface.
To implement Runnable, a class only need to implement a single method called run().
Inside run () we will define the code that constitute the new thread.
When a new thread creates, it do not executes until we call its start () method. When start () method executes it call to run() method.

Below is the multithreading program in java with implementing runnable interface

Example: Print hello to illustrate multithreading example in java

public class ThreadTest1 implements Runnable{
	public void run(){
		System.out.println("Hello from run");
	}
	public static void main(String[] s){
		ThreadTest tt=new ThreadTest();
		Thread t=new Thread(tt);
		t.start();
	}
}

public class ThreadTest1 implements Runnable{

public void run(){

System.out.println("Hello from run");

}

public static void main(String[] s){

ThreadTest tt=new ThreadTest();

Thread t=new Thread(tt);

t.start();

}

Output

Hello from run

1	Hello from run

Creating more than one thread in java :- multithreading in java example

public class ThreadTest3 implements Runnable{
	public void run(){
		try{
        for (int i=0 ;i<10;i++){
          System.out.println("Hello from run "+i);
          Thread.sleep(5000);
        }
     }
     catch(InterruptedException e){
        System.out.println("InterruptedException " +e);
     }
	}
	public static void main(String[] s){
		ThreadTest3 tt=new ThreadTest3();
		Thread t=new Thread(tt);
		t.start();
		Thread t1=new Thread(tt);
		t1.start();
	}
}

public class ThreadTest3 implements Runnable{

public void run(){

try{

for (int i=0 ;i<10;i++){

System.out.println("Hello from run "+i);

Thread.sleep(5000);

}

catch(InterruptedException e){

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

}

public static void main(String[] s){

ThreadTest3 tt=new ThreadTest3();

Thread t=new Thread(tt);

t.start();

Thread t1=new Thread(tt);

t1.start();

}

Output

Hello from run 0
Hello from run 0
Hello from run 1
Hello from run 1
Hello from run 2
Hello from run 2
Hello from run 3
Hello from run 3
Hello from run 4
Hello from run 4
Hello from run 5
Hello from run 5
Hello from run 6
Hello from run 6
Hello from run 7
Hello from run 7
Hello from run 8
Hello from run 8
Hello from run 9
Hello from run 9

Hello from run 0

Hello from run 1

Hello from run 2

Hello from run 3

Hello from run 4

Hello from run 5

Hello from run 6

Hello from run 7

Hello from run 8

Hello from run 9

Another Example of Thread is

class Demo implements Runnable {
    Thread t;
    Demo() { // creating a new, second thread
        t = new Thread(this, "DemoThread");
        System.out.println("Child Thread= " + t);
        t.start(); // start a thread & call run()
    }
    public void run() {
        try {
            for (int i = 5; i > 0; i--) {
                System.out.println("Child Thread: " + i);
                Thread.sleep(500); // Let the thread sleep for a while.
            }
        } catch (InterruptedException e) {
            System.out.println("Child exception ");
        }
        System.out.println("exit child thread");
    }
}



public class CreateThread {
    public static void main(String args[]) {
        new Demo();
        try {
            for (int i = 5; i > 0; i--) {
                System.out.println(" Main Thread: " + i);
                Thread.sleep(1000); // Let the thread sleep for a while.
            }
        } catch (InterruptedException e) {
            System.out.println("main exception ");
        }
        System.out.println("exit main thread");
    }
}

class Demo implements Runnable {

Thread t;

Demo() { // creating a new, second thread

t = new Thread(this, "DemoThread");

System.out.println("Child Thread= " + t);

t.start(); // start a thread & call run()

}

public void run() {

try {

for (int i = 5; i > 0; i--) {

System.out.println("Child Thread: " + i);

Thread.sleep(500); // Let the thread sleep for a while.

}

} catch (InterruptedException e) {

System.out.println("Child exception ");

}

System.out.println("exit child thread");

}

public class CreateThread {

public static void main(String args[]) {

new Demo();

try {

for (int i = 5; i > 0; i--) {

System.out.println(" Main Thread: " + i);

Thread.sleep(1000); // Let the thread sleep for a while.

}

} catch (InterruptedException e) {

System.out.println("main exception ");

}

System.out.println("exit main thread");

}

Result

Child Thread= Thread[DemoThread,5,main]
Child Thread: 5
 Main Thread: 5
Child Thread: 4
 Main Thread: 4
Child Thread: 3
Child Thread: 2
 Main Thread: 3
Child Thread: 1
exit child thread
 Main Thread: 2
 Main Thread: 1
exit main thread

Child Thread= Thread[DemoThread,5,main]

Child Thread: 5

Main Thread: 5

Child Thread: 4

Main Thread: 4

Child Thread: 3

Child Thread: 2

Main Thread: 3

Child Thread: 1

exit child thread

Main Thread: 2

Main Thread: 1

exit main thread

Description:

Passing “this” as a argument, “DemoThread” is the name of the thread.

In this program, main thread fineshes last because the main thread sleeps for 1000 milliseconds (1 seconds) between iteration, but the child thread sleeps for only 500 milliseconds.

This cause the child thread terminates earlier than main thread.

B Creating Thread By extending Thread class in java

To create a thread we will create a thread a class that extends Thread class.
To extend Thread class, a class only needs to implement a single method called run (). This extending class must override the run() method
Inside run () we will define the code that constitute the new thread.
When a new thread creates, it do not executes until we call its start () method. When start () method executes it call to run() method.

Simple Thread example in java

Example: Write a thread program in java by extending thread class.

public class ThreadTest extends Thread{
	public void run(){
		System.out.println("Hello from run");
	}
	public static void main(String[] s){
		ThreadTest t=new ThreadTest();
		t.start();
	}
}

public class ThreadTest extends Thread{

public void run(){

System.out.println("Hello from run");

}

public static void main(String[] s){

ThreadTest t=new ThreadTest();

t.start();

}

Hello from run

1	Hello from run

Multithreading in Java example programs

Example: Write a program to show multithreading in java by extending thread class

public class ThreadTest extends Thread{
	public void run(){
		System.out.println("Hello from run");
	}
	public static void main(String[] s){
		ThreadTest t=new ThreadTest();
		t.start();
	}
}

public class ThreadTest extends Thread{

public void run(){

System.out.println("Hello from run");

}

public static void main(String[] s){

ThreadTest t=new ThreadTest();

t.start();

}

Hello from run 0
Hello from run 0
Hello from run 1
Hello from run 1
Hello from run 2
Hello from run 2
Hello from run 3
Hello from run 3
Hello from run 4
Hello from run 4
Hello from run 5
Hello from run 5
Hello from run 6
Hello from run 6
Hello from run 7
Hello from run 7
Hello from run 8
Hello from run 8
Hello from run 9
Hello from run 9

Hello from run 0

Hello from run 1

Hello from run 2

Hello from run 3

Hello from run 4

Hello from run 5

Hello from run 6

Hello from run 7

Hello from run 8

Hello from run 9

Multithreading in java example using Thread class

class Demo extends Thread {
    Demo() {
        super("DemoThread"); // creating a new, second thread	
        System.out.println("Child Thread= " + this);
        start(); // start a thread
        }
        public void run() // entry point for  new Thread
        {
            try {
                for (int i = 5; i > 0; i--) {
                    System.out.println("Child Thread: " + i);
                    Thread.sleep(500); // thread sleep for a while.
                }
            } catch (InterruptedException e) {
                System.out.println("Child exception ");
            }
            System.out.println("exit child thread");
        }
    }
    public class Test {
        public static void main(String args[]) {
            new Demo(); // call constructor
            try {
                for (int i = 5; i > 0; i--) {
                    System.out.println(" Main Thread: " + i);
                    Thread.sleep(1000); //  thread sleep for a while.	
                }
            } catch (InterruptedException e) {
                System.out.println("main exception ");
            }
            System.out.println("exit main thread");
        }
    }

class Demo extends Thread {

Demo() {

super("DemoThread"); // creating a new, second thread

System.out.println("Child Thread= " + this);

start(); // start a thread

}

public void run() // entry point for new Thread

{

try {

for (int i = 5; i > 0; i--) {

System.out.println("Child Thread: " + i);

Thread.sleep(500); // thread sleep for a while.

}

} catch (InterruptedException e) {

System.out.println("Child exception ");

}

System.out.println("exit child thread");

}

public class Test {

public static void main(String args[]) {

new Demo(); // call constructor

try {

for (int i = 5; i > 0; i--) {

System.out.println(" Main Thread: " + i);

Thread.sleep(1000); // thread sleep for a while.

}

} catch (InterruptedException e) {

System.out.println("main exception ");

}

System.out.println("exit main thread");

}

Result

Child Thread= Thread[DemoThread,5,main]
 Main Thread: 5
Child Thread: 5
Child Thread: 4
 Main Thread: 4
Child Thread: 3
Child Thread: 2
 Main Thread: 3
Child Thread: 1
exit child thread
 Main Thread: 2
 Main Thread: 1
exit main thread

Child Thread= Thread[DemoThread,5,main]

Main Thread: 5

Child Thread: 5

Child Thread: 4

Main Thread: 4

Child Thread: 3

Child Thread: 2

Main Thread: 3

Child Thread: 1

exit child thread

Main Thread: 2

Main Thread: 1

exit main thread

4 Thread Methods in Java

Commonly used methods of Thread class are as follows

Sr No	Method and Description
1	void run() Work execute as a thread is defined in this method .
2	void start() Used to start a thred which Calls the run() method of the thread or child class.
3	static void sleep(long miliseconds) Suspend the thread for specified amount of time.
4	static void sleep(long miliseconds,int nanos) Suspend the thread for specified amount of time.
5	void join() This method is used to pause the ececution of current thread until it die. void join().
6	void join(long miliseconds) Pause the execution of current thread for the pecified miliseconds.
7	void join(long miliseconds,int nanos) Pause the execution of current thread for the pecified miliseconds and nano seconds.
8	boolean isAlive() To checks a thread is alive or not.
9	String getName() Returns the name of the thread.
10	setName(String name) Used to set the name of thread.
11	int getPriority() Get the priority of the thread.
12	void setPriority(int priority) Set the priority of thread.
13	static Thread currentThread() Returns the reference of currently executing thread
14	long getId() Returns the id of the thread.
15	static void yield() Temporarily pause the currently executing thread and allow other threads to execute.
16	void suspend() Used to suspend the thread.
17	void resume() Used to resume the suspended thread.
18	void stop() Used to stop the thread.
19	void interrupt() Interrupts the thread.
20	boolead isInterrupted() Check whether the thead is interrupted or not

Use of thread in java

To Reduce the time of execution of a program
To achieve parallel execution

Thread Life Cycle in Java

How many ways to create thread in java

There are two ways to create thread in java

By Extending Thread class
By Implementing runnable Interface.

Types of thread in java

Daemon thread provide services to other threads
User defined threads Created by User

How to perform two tasks by two threads ?

class Thread1 extends Thread {
    public void run() {
        System.out.println("Hello Friends");
    }
}
class Thread2 extends Thread {
    public void run() {
        System.out.println("Bye Friends");
    }
}
public class TreadExample {
    public static void main(String[] args) {
        Thread1 t = new Thread1();
        t.start();
        Thread2 t2 = new Thread2();
        t2.start();
    }
}

class Thread1 extends Thread {

public void run() {

System.out.println("Hello Friends");

}

class Thread2 extends Thread {

public void run() {

System.out.println("Bye Friends");

}

public class TreadExample {

public static void main(String[] args) {

Thread1 t = new Thread1();

t.start();

Thread2 t2 = new Thread2();

t2.start();

}

Hello Friends
Bye Friends

1 2	Hello Friends Bye Friends

Real time example of multithreading in java

When two or more I/O operations are not dependent of each other then we can perform them by different threads.
When tow or more Database read/write operations are not dependent then we can perform using multithreads.
Sending OTP on mobile and email id at same time.
Adding post on social media (fb, twitter, pintrest etc) on one click using publisher software.
Servers are multithreaded they create separate thread to handle each request.

Java multithreading programming exercises

Create Two threads using Thread class.
Create Two threads using runnable Interface.
Implement Produces consumer problem in Java.

Packages in Java -Types Sub Packages and Examples

Packages in Java is one of the important concept. All Java classes and interfaces are arranged in package structure.

What is package in java

Packages is a namespace which contains related classes and Interfaces.

The methods and field of class define inside the package can be accessible in package outside package and in child classes based on access specifier.

Packages are stored in a hierarchical manner and explicitly imported into a new class definition.

Types of packages in java

Java packages are classified into two types

Predefined or Built-in package
User defined package

1 Java API(Application Programming Interface) packages or Predefined packages or Built-in packages

These packages are defined by the system. Some example of system defined packages are

java.lang: It contains fundamental classes like System, String Math, Number etc. This is the default package in java.
java.util: This package contains collections framework, legacy collection classes, event model and other features.
java.io: Provides system input output with stream classes and files
java.awt: Contain classes for creating user interface graphic and Image classes.
java.net: Contains classes related to networking and sockets
The Java 1.3 contains nearly 60 predefined packages

Importing packages in Java with Example

import java.util.Scanner; -To import Scanner class

import java.util.*; To import all classes in util package

import java.util.Scanner;

public class ScannerTest{

    public static void main(String [] s){
	
		Scanner scanner=new Scanner(System.in);
		System.out.println("Enter your Name");
		String name=scanner.nextLine();
		System.out.println("Enter your Age");
		int age=scanner.nextInt();
		System.out.println("Hello From main "+name +" "+age);
		
	}
	
	}

import java.util.Scanner;

public class ScannerTest{

public static void main(String [] s){

Scanner scanner=new Scanner(System.in);

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

String name=scanner.nextLine();

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

int age=scanner.nextInt();

System.out.println("Hello From main "+name +" "+age);

}

Here we import is used to import java.util.Scanner;

2 User defined packages in java

These packages are defined by the user.

How to create package in java

Defining as packages: To define a package, place “package” command as the first statement in the source file.

The syntax of packages creation :-

package  package_name;

1	package package_name;

mypackage;   
public class number {

    public void add(int a, int b) {
        System.out.println(" a + b =" + (a + b));
    }
}

mypackage;

public class number {

public void add(int a, int b) {

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

}

The class that is defined in the package must be public. So that is can be accessible by any another of them.
Java uses the file system file directories to store packages. We save the program with number.java and compile the package is as javac_d/number.java. Due to this compilation Mypackage directory is automatically created and .class file is stores in that directory.

Once the package creation has completed. Then the package information is including with the help of “import” keyword. import keyword links the package with our program.

Java Package Example

It is place before the class definition:

import mypack.*;  
or    
import mypack.number;

import mypack.*;

import mypack.number;

package x;	// package x          

public class Number // file name must be saver with class name(number.java)        
{

    public void add(int a, int b) {
        System.out.println(" sum =" + (a + b));

    }
}

package y; 									           

import x.number;


public class Test {

    public static void main(String a[]) {
        number ob = new number();
        ob.add(10, 20);
    }
}

package x; // package x

public class Number // file name must be saver with class name(number.java)

{

public void add(int a, int b) {

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

}

package y;

import x.number;

public class Test {

public static void main(String a[]) {

number ob = new number();

ob.add(10, 20);

}

sum = 30

sum = 30

In this program, package is within x folder and main program is within y folder in c drive.
Package name in this program is x.
File name and package class name must be same ex: (number.java- source file).

How to compile package in java

c:\> javac folder/filename.java

c:\>java package.filename

javac  directory/filename
c:\>javac   x/number.java
c:\>javac   y/xyz.java
c:\>java     y.xyz

javac directory/filename

c:\>javac x/number.java

c:\>javac y/xyz.java

c:\>java y.xyz

package  math1;	// package within math1 folder	

public class Cal // file name must be saver with class name(Cal.java)
{

    public void square(int a) {
        System.out.println(" Square =" + (a * a));
    }

    public void cube(int a) {
        System.out.println(" Cube =" + (a * a * a));
    }

}

package math1; // package within math1 folder

public class Cal // file name must be saver with class name(Cal.java)

{

public void square(int a) {

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

}

public void cube(int a) {

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

}

package x; 


import math1.Cal;

public class Test {

    public static void main(String a[]) {
        Cal ob = new Cal();
        ob.square(10);
        ob.cube(10);
    }
}

package x;

import math1.Cal;

public class Test {

public static void main(String a[]) {

Cal ob = new Cal();

ob.square(10);

ob.cube(10);

}

   square = 100
   cube = 1000

1 2	square = 100 cube = 1000

Note: If we want to access all the classes of information then the classes are stored in different files with the same package name.

Sub Packages

In Java, it is possible to create a sub packages for the main packages.

Syntax

package pack1.pack2;

 package  pack1.pack2;

1	package pack1.pack2;

Where pack1 is the main package and pack2 is the sub package.

Java packages sub package example

 package  pack1;

public class x {

    public void show() {
        System.out.println(" super");
    }

}

package pack1;

public class x {

public void show() {

System.out.println(" super");

}

package pack1.pack2;
public class y {

    public void display() {
        System.out.println("sub");
    }
}

package pack1.pack2;

public class y {

public void display() {

System.out.println("sub");

}

package z;
import	pack1.x;								            

import	pack1.pack2.y;								
public class Test {

    public static void main(String a[]) {
        x ob1 = new x();
        ob1.show();
        y ob2 = new y();
        ob2.display();
    }
}

package z;

import pack1.x;

import pack1.pack2.y;

public class Test {

public static void main(String a[]) {

x ob1 = new x();

ob1.show();

y ob2 = new y();

ob2.display();

}

Result

   super
   sub

super

sub

How many predefined packages in java

As per different java versions there are different packages and classes this SO question is also helpful.

We Inspected javase 14 and find there are 225 predefined packages / sub packages in java.

Which Package is default package in java

The package which is not required to import explicitly is known as default package.

If we write simple program to print hello then there we use System, String class we don’t need to import that. These are defined in java.lang package.

Default Package in Java is java.lang

Which keyword is used for accessing the features of a package

The import keyword is used for accessing the features of a package.

We can import classes and interfaces in our current file using import.

What is Import in Java

Import in a keyword in java. We use import statement to import class or all classes from a package.

How to import a package in java

import java.util.Date; or
import java.util.*;

How to create a package in java (Steps to create package in java with example)

Create a folder with package name
Create java files inside folder
each java files include package definition package packagename;

packages in java with example program

package one;

public class First{
	
    public static void main(String[] s){
	System.out.println("Hello From one.First");
}
}

package one;

public class First{

public static void main(String[] s){

System.out.println("Hello From one.First");

}

D:\>javac one/First.java
D:\>java one.First
Hello From one.First

D:\>javac one/First.java

D:\>java one.First

Hello From one.First

How to run package program in java (How to execute package in java)

compile d:\>javac foldername/filename.java run d:\>java packagename.filename

What is java lang package in java

java lang (java.lang) is default package in Java. It contains fundamental classes.

Use of packages in java

Group related classes and interfaces
To avoid Naming conflicts
To provide Access Control

Example of predefined packages in java

Predefined packages are defend by Java Team like

java.lang (default package)
java.util
java.io
java.net
java.math
java.sql
java.time
java.awt
java.text

view all

The package which should be created to categorize the package further

The package which should be created to categorize the package further is sub package

java package java.

sub packages java.land, java.util etc.

Which of the following is used to avoid naming conflicts?

class
Interface
package
templet

Answer is package

Reference

Java Package

Login page in awt applet Java

Creating Login page in awt applet is easy.

Here we are not using any layout.

Steps by step process to develop this program is as below

Declare Label, JTextField, JPasswordField and Button
Inside init() create object for JLabel, JTextField and JPasswordField and Button
setBounds() to show elements in specific position.
set Container layout to null setLayout(null);
add all elements to container using add()
set size of container setSize(400, 300);
addActionListener() to login and reset button
override actionPerformed() for login and reset
on click on login button if username is Bond007 and password in James007 then show message Dialog Successfully Login
if username and password is incorrect then show message Dialog Opps username/ password is incorrect
on click on reset button reset the values of username and password field

Login page in awt applet Example

package APDemo;
import java.applet.Applet;
import java.awt.Button;
import java.awt.Color;
import java.awt.Label;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JOptionPane;
import javax.swing.JPasswordField;
import javax.swing.JTextField;

public class LoginPage extends Applet {

    Label userNameLabel, passwordLabel;
    JTextField userName;
    JPasswordField password;

    public void init() {

        userNameLabel = new Label("User Name");
        userName = new JTextField(20);
        userName.setText("User Name");
        passwordLabel = new Label("Password");
        password = new JPasswordField(20);
        password.setText("Password");
        password.setEchoChar('#');
        login = new Button("Login");
        reset = new Button("Reset");
        userNameLabel.setBounds(10, 10, 100, 20);
        userName.setBounds(150, 10, 150, 20);
        passwordLabel.setBounds(10, 50, 100, 20);
        password.setBounds(150, 50, 150, 20);
        login.setBounds(50, 100, 100, 20);
        login.setBackground(Color.GREEN);
        reset.setBounds(200, 100, 100, 20);
        reset.setBackground(Color.CYAN);
        //set applet layout to null
        setLayout(null);
        //add elements to applet
        add(userNameLabel);
        add(userName);
        add(passwordLabel);
        add(password);
        add(login);
        add(reset);

        //set size of applet
        setSize(400, 300);

        //login button click
        login.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent ae) {
                String uname = userName.getText().toString();
                String passwd = password.getText().toString();
                System.out.println("User Name :" + uname);
                System.out.println("Password :" + passwd);
                if (uname.equals("Bond007") && passwd.equals("James007")) {
                    JOptionPane.showMessageDialog(null, "Successfully Login");
                } else {
                    JOptionPane.showMessageDialog(null, "Opps username/ password is incorrect");
                }

            }
        });
        //reset button click
        reset.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent ae) {
                userName.setText("");
                password.setText("");

            }
        });

    }
}

package APDemo;

import java.applet.Applet;

import java.awt.Button;

import java.awt.Color;

import java.awt.Label;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.swing.JOptionPane;

import javax.swing.JPasswordField;

import javax.swing.JTextField;

public class LoginPage extends Applet {

Label userNameLabel, passwordLabel;

JTextField userName;

JPasswordField password;

public void init() {

userNameLabel = new Label("User Name");

userName = new JTextField(20);

userName.setText("User Name");

passwordLabel = new Label("Password");

password = new JPasswordField(20);

password.setText("Password");

password.setEchoChar('#');

reset = new Button("Reset");

userNameLabel.setBounds(10, 10, 100, 20);

userName.setBounds(150, 10, 150, 20);

passwordLabel.setBounds(10, 50, 100, 20);

password.setBounds(150, 50, 150, 20);

reset.setBounds(200, 100, 100, 20);

reset.setBackground(Color.CYAN);

//set applet layout to null

setLayout(null);

//add elements to applet

add(userNameLabel);

add(userName);

add(passwordLabel);

add(password);

add(login);

add(reset);

//set size of applet

setSize(400, 300);

//login button click

@Override

public void actionPerformed(ActionEvent ae) {

String uname = userName.getText().toString();

String passwd = password.getText().toString();

System.out.println("User Name :" + uname);

System.out.println("Password :" + passwd);

if (uname.equals("Bond007") && passwd.equals("James007")) {

JOptionPane.showMessageDialog(null, "Successfully Login");

} else {

JOptionPane.showMessageDialog(null, "Opps username/ password is incorrect");

}

});

//reset button click

reset.addActionListener(new ActionListener() {

@Override

public void actionPerformed(ActionEvent ae) {

userName.setText("");

password.setText("");

}

});

}

Elements are placed in specific position using setBound().

Buttons click events are bind using ActionListener and handled by actionPerformed.

We handled events like below.

login.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent ae) {
             }
}

@Override

public void actionPerformed(ActionEvent ae) {

}

You can handle actionPerformed() separately for that you have to implement ActionListener in your class.

You can run and check Program output

Hope you Got this.

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