Java ClassCastException: Understanding and Fixing Runtime Errors

This code will result in a ClassCastException at runtime.

On line 3, a new Dog object is created and assigned to an Animal reference variable 'a'. Since Dog extends Animal, this is perfectly valid.

However, on line 4, the code attempts to cast 'a' to a Cat object and call the 'catchMouse()' method. Since 'a' is actually a Dog object, and Dog does not have a 'catchMouse()' method, a ClassCastException will occur at runtime.

To fix this error, either create a new Cat object and assign it to 'a', or remove the cast and call a method that is present in both Dog and Cat (such as 'eat()').