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

ClassA a = <something>;
ClassB b = (ClassB) a;

The 2nd line will fail if ClassA is not a subclass of ClassB, and will throw a ClassCastException.

Answer 2

To avoid x !instance of Long prob Add

<property name="openjpa.Compatibility" value="StrictIdentityValues=false"/>

in your persistence.xml

Answer 3

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 4

It's because you're casting to the wrong thing - you're trying to convert to a particular type, and the object that your express refers to is incompatible with that type. For example:

Object x = "this is a string";
InputStream y = (InputStream) x; // This will throw ClassCastException

If you could provide a code sample, that would really help...

Answer 5

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;
}

Answer 6

@Laurențiu Dascălu's answer explains how / why you get a ClassCastException.

Your exception message looks rather suspicious to me, but it might help you to know that "[Lcom.rsa.authagent.authapi.realmstat.AUTHw" means that the actual type of the object that you were trying to cast was com.rsa.authagent.authapi.realmstat.AUTHw[]; i.e. it was an array object.

Normally, the next steps to solving a problem like this are:

• examining the stacktrace to figure out which line of which class threw the exception,
• examining the corresponding source code, to see what the expected type, and
• tracing back to see where the object with the "wrong" type came from.