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.authagent.authapi.realmstat.AUTHw 

Answer 1

According to the documentation:

Thrown to indicate that the code has attempted to cast an Object to a subclass of which it is not an instance. For example, the following code generates a ClassCastException:

Object x = new Integer(0); System.out.println((String)x);  

Answer 2

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; }