Abstract Classes

class Boat extends Vehicle

{

  void turn(int angle) { ... }

}

An abstract class is one not intended for direct creation; creation is only implied as a general case of a more specific class.

Vehicle v;

v = new Vehicle();   wrong Vehicle is abstract

v = new Automobile();   ok

v = new Boat();         ok

• A class with at least one abstract method must  be declared abstract.
• A class with no  abstract methods may be abstract or not.
• An abstract class may have non-abstract methods, e.g. methods which call  other abstract methods.
• An abstract class can contain fields.

Examples ObjectDraw.java (Run this applet.)