Explanation of ClassCastException in Java

Solution 1:

Straight from the API Specifications for the ClassCastException:

Thrown to indicate that the code has attempted to cast an object to a subclass of which it is not an instance.

So, for example, when one tries to cast an Integer to a String, String is not an subclass of Integer, so a ClassCastException will be thrown.

Object i = Integer.valueOf(42);
String s = (String)i;            // ClassCastException thrown here.

Solution 2:

It's really pretty simple: if you are trying to typecast an object of class A into an object of class B, and they aren't compatible, you get a class cast exception.

Let's think of a collection of classes.

class A {...}
class B extends A {...}
class C extends A {...}

1. You can cast any of these things to Object, because all Java classes inherit from Object.
2. You can cast either B or C to A, because they're both "kinds of" A
3. You can cast a reference to an A object to B only if the real object is a B.
4. You can't cast a B to a C even though they're both A's.