User defined exception in java

User Defined Exception or custom exception is creating user own exception class and throws that exception using ‘throw’ keyword. User-defined exception must extend Exception class.

In order to create custom exception, it is needed to extend Exception class that belongs to java.lang package.

Ex:

class JavaException{

public static void main(String args[]){

  try{

      throw new MyException(2);      

// throw is used to create a new exception and throw it.

  }

 catch(MyException e){  

System.out.println(e) ;

 }

}

}

class MyException extends Exception{

int a;  

MyException(int b) {    

a=b;

   }

 
public String toString(){

    
return ("Exception Number = "+a) ;

  }

}