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Throw keyword in java

  • Throw keyword is used to throw exception manually.
  • Whenever it is required to suspend the execution of the functionality based on the user defined logical error condition we will use this throw keyword to throw exception.
  • So we need to handle these exceptions also using try catch blocks.



 Java simple example Program to explain use of throw keyword in java


  1. package exceptions;
  2.  
  3. public class ThrowKeyword {
  4.  
  5.     
  6. public static void main(String[] args) {
  7.  
  8. try {
  9.             
  10.    throw new ArithmeticException();
  11.             
  12.             
  13. } catch (Exception e) {
  14.  
  15.    System.out.println(e);
  16.    e.printStackTrace();
  17. }
  18.  
  19. }
  20.  
  21. }

Output:



  1. java.lang.ArithmeticException
  2. java.lang.ArithmeticException
  3.     at exceptions.ThrowKeyword.main(ThrowKeyword.java:11)

Rules to use "throw" keyword in java
  • throw keyword must follow Throwable type of object.
  • It must be used only in method logic.
  • Since it is a transfer statement , we can not place statements after throw statement. It leads to compile time error Unreachable code



throw keyword in java


  •  We can throw user defined exception using throw keyword.

  1. //Custom exception
  2. package com.instanceofjavaforus;
  3. public class InvalidAgeException extends Exception {
  4.  InvaidAgeException(String msg){
  5.  super(msg);
  6.  }
  7. }
     

  1. package com.exceptions;
  2. public class ThrowDemo {

  3. public boolean isValidForVote(int age){
  4.  
  5.  try{
  6.    if(age<18){
  7.   throw new InvalidAgeException ("Invalid age for voting");
  8. }
  9.  }catch(Exception e){
  10.  System.out.println(e);
  11.  }
  12.   return false;
  13.  }
  14.  
  15. public static void main(String agrs[]){
  16.  
  17.  ThrowDemo obj= new ThrowDemo();
  18.    obj.isValidForVote(17);
  19.  
  20.   }
  21. }


 Output:


  1.  exceptions.InvalidAgeException: Invalid age for voting
  • We can throw predefined exceptions using throw keyword


  1. package com.instanceofjava;
  2.  
  3. public class ThrowKeyword{
  4. public void method(){
  5.  
  6.  try{
  7.   
  8.   throw new NullPointerException("Invalid age for voting");
  9. }
  10.  }catch(Exception e){
  11.  System.out.println(e);
  12.  }
  13.  }
  14.  
  15.   public static void main(String agrs[]){
  16.  
  17.  ThrowKeyword obj= new ThrowKeyword();
  18.  
  19.    obj.method();
  20.  
  21.   }
  22. }

 Output:


  1.  java.lang.NullPointerException: Invalid age for voting

Instance Of Java

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