java.lang.ClassCastException

Question

Normally whats the reason to get java.lang.ClassCastException ..? I get the following error in my application

java.lang.ClassCastException: [Lcom.rsa.authag         


        

Answer 1

A ClassCastException ocurrs when you try to cast an instance of an Object to a type that it is not. Casting only works when the casted object follows an "is a" relationship to the type you are trying to cast to. For Example

Apple myApple = new Apple();
Fruit myFruit = (Fruit)myApple;

This works because an apple 'is a' fruit. However if we reverse this.

Fruit myFruit = new Fruit();
Apple myApple = (Apple)myFruit;

This will throw a ClasCastException because a Fruit is not (always) an Apple.

It is good practice to guard any explicit casts with an instanceof check first:

if (myApple instanceof Fruit) {
  Fruit myFruit = (Fruit)myApple;
}