Essay

Abstract

Abstract Methods and Classes

An abstract class is a class that is declared abstract—it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed. An abstract method is a method that is declared without an implementation (without braces, and followed by a semicolon), like this: abstract void moveTo(double deltaX, double deltaY); If a class includes abstract methods, then the class itself must be declared abstract, as in: public abstract class GraphicObject { // declare fields // declare nonabstract methods abstract void draw(); } When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class.

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