What does 'classcastexception in java' mean?

Example:

Object str = "Hello";
Integer num = (Integer) str;

Solution:

This error arises when you try to cast an object of one type to another incompatible type. Ensure that the object you're casting is of the desired type or can be casted to that type.

Object str = "Hello";
if(str instanceof Integer) {
    Integer num = (Integer) str;
}