In java programming, If the exception occurs within the try block it is thrown.
Throw and Throws Keywords in Java is very important to throw exceptions.
a throw keyword is used to throw an exception
A system-gener
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
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | 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); } } } |
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 chances 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 Java programming, the 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:
1 2 | type method_name(parameter list) throws exception1, exception2 ….{ } |
Here, exception1, and exception2 are commas, a list of the exception that a method can throw.
Example of throws
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | 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); } } } |
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” as the name of the 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)
The throw keyword is used to throw an exception from the method or from a block
the throw is used inside the method
throw new NullPointerException("demo");
throws keyword is used to inform that a method throws an exception(s)
throws keyword is used in the method header
public Scanner(File source) throws FileNotFoundException
What is the purpose of the throw statement?
The throw is used to throw an exception from a method or from a 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.
Create your own Exception: User-Defined exception in Java
The ______ keyword is used to manually throw an exception in java
The Throw keyword is used to manually throw an exception.
We covered Throw and Throws Keywords in Java go through following links for more.
Read More
- Exception Handling in Java: Hierarchy Example and Types
- Exception Handling in Java with Examples
- Exception Handling try catch finally blocks in Java
Reference