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.

In this tutorial you’ll learn how to work with static member classes and the three types of inner classes in your Java programs ... public abstract class Ellipse2D extends RectangularShape ...

Interfaces, however, support multiple inheritances where abstract classes don't. Implementation is done similarly in Java. For example, using the keyword implements will make a Java interface, while ...

The Java code below shows the details of how to use a variant of Abstract Factory design ... to an object dynamically. A good example is Strategy design pattern. A parameter may be used to decide ...