» » Difference between throw and throws in java


Throw:

 

  • throw keyword used to throw user defined exceptions.(we can throw predefined exception too)
  • If we are having our own validations in our code we can use this throw keyword.
  • For Ex: BookNotFoundException, InvalidAgeException (user defined) 




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

  1. package com.instanceofjavaforus;
  2. public class ThrowDemo {
  3. public void method(){
  4.  try{
  5.   
  6.   throw new NullPointerException("Invalid age for voting");
  7. }
  8.  }catch(Exception e){
  9.  System.out.println(e);
  10.  }
  11.  }
  12.   public static void main(String agrs[]){
  13.  ThrowDemo obj= new ThrowDemo();
  14.    obj.method();
  15.   }
  16. }
Like this we can throw checked exceptions and unchecked exceptions also. But throw keyword is mainly used to throw used defined exceptions / custom exceptions.

Throws:

  • The functionality of throws keyword is only to explicitly to mention that the method is proven transfer un  handled exceptions to the calling place.

  1. package com.instanceofjavaforus;
  2. public class ThrowSDemo {
  3. public void method(int a,int b) Throws ArithmeticException{
  4.  
  5. inc c= a/b;
  6.  }
  7.   public static void main(String agrs[]){
  8.  ThrowDemo obj= new ThrowDemo();
  9.    try{
  10. obj.method(1,0);
  11. }catch(Exception e){
  12.  System.out.println(e);
  13. }
  14.   }
  15. }

 Uses of throws keyword:

  • Using throws keyword we can explicitly provide the information about unhand-led exceptions of the method to the end user, Java compiler, JVM.
  • Using throws keyword we can avoid try-catch with respect to the statements which are proven to generate checked exceptions.
  • It us highly recommended not to avoid try-catch with respect to the statements which are proven to generate exceptions in main method using throws keyword to the main() method.



Instance Of Java

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