It’s a good idea to use an abstract class when you need to implement mutable state. As an example, the Java Collections Framework includes the AbstractList class, which uses the state of variables.

You can see this in the example below, featuring Duke and Juggy: public abstract ... ("The Java Mascot is about to execute an action!"); } } public class Duke extends JavaMascot { @Override ...

When modeling an abstract ... an anonymous class. 1 This example uses a form of switch expression -- one that uses patterns as case labels -- that is not yet supported by the Java Language.