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.