Could you explain what a ClassCastException means in Java and under what conditions it occurs?

A ClassCastException in Java occurs when a program attempts to cast an object to a type that it does not belong to or is not a subclass of. It is a runtime error related to incorrect type casting.

For example, if you have an object of class Animal, and you try to cast it to class Dog, but the object is not actually an instance of Dog, a ClassCastException will be thrown.

Example:

Object obj = new String("test");
Integer num = (Integer) obj; // ClassCastException, because obj is not an Integer

To avoid this error, you can use the instanceof operator to check if the object belongs to the required class before casting.