Holiday

Abstract classes are used to organize the "concept" of something that has several different versions in the children. An abstract class can include abstract methods and non-abstract methods.

Here is a class definition for class Holiday. It is a non-abstract child of an abstract parent:

class Holiday extends Card
{
  public Holiday( String r )
  {
    recipient = r; // recipient in Card is protected, so this works
  }

  public void greeting()
  {
    System.out.println("Dear " + recipient + ",");
    System.out.println("Season's Greetings!\n");
  }
}

The class Holiday is not an abstract class. Objects can be instantiated from it. Its constructor implicitly calls the no-argument constructor in its parent, Card, which calls the constructor in Object. So even though it has an abstract parent, a Holiday object is just as much an object as any other.

• Holiday inherites the abstract method greeting() from its parent.
• Holiday must define a greeting() method that includes a method body (statements between braces).
• The definition of greeting() must match the signature given in the parent.
• If Holiday did not define greeting(), then Holiday must be declared to be an abstract class.
  • This would make it an abstract child of an abstract parent.