Defining Classes

Previously, we examined how objects from a given class can be instantiated and used. Our next goal is to look at the code which defines a Class.

For this purpose, we will examine the CyberPet Case Study, which is an ongoing example from the text. It is introduced in Ch. 2, and expanded throughout Ch. 3. In class, we started with the initial version of the CyberPet, as definined in Figure 2-8 and then built up to the version given in Figure 3-10.

The outline of issues discussed in that context includes:

• The Declaration of a Class
  • implicitly extends Object
  • delcaring instance variables
  • declaring class methods
• Use of matching curly brackets ( { } ) to demarcate blocks of code
• keywords: return, void
• Qualified names (e.g., System.out.println(), csa120.shape.Canvas)
• Scope of variables (e.g., class vs. local)
• Variable initialization and default values
• Constructor (this method name must be same as the class name, and the return value is implicitly a reference to the newly created object)
• String contatenation operator
• Use of parameters and return values
• Constructor Overloading and Method Signatures