Objectives

The objectives of this lab are to:

• Understand the ideas behind abstraction
• Sucessfully implement abstraction in the Network system.

Network-V5

In this step, you will create version 5 of the Network system (our menu driven messaging system). In this version, you will use abstraction in the inheritance hierarchy.

Abstraction in Network-V5

• In Eclipse, create a new project called Network-V5.

• Copy the following classes into this new project:

  • PhotoPost
  • MessagePost
  • Post
  • NewsFeed
  • Driver

• Make the Post class abstract and add an abstract method called displayExcerpt() to it. The return type of this method should be a String.

• In Post's subclasses, provide the concrete implementation for this method.

• Message Post code:

    public String displayExtract()
    {
        return "Message extract "+ message.substring(0,10) + "....";
    }

• PhotoPost code:

    public String displayExtract()
    {
        return "Photo caption: " + caption.substring(0,10) + "....";
    }

• Save your code.

• Note that this code does not "do" anything as we have not called the displayExtract method from anywhere. This is just a very short lab to illustrate the abstract class and method concept.

Solution: Network-V5