Ivor Horton's Beginning Java™ 2, JDK™ 5th Edition

5.2. Defining Classes

To define a class you use the keyword class followed by the name of the class, followed by a pair of braces enclosing the details of the definition. Let's consider a concrete example to see how this works in practice. The definition of the Sphere class that I mentioned earlier could be:

class Sphere {
  static final double PI = 3.14;       // Class variable that has a fixed value
  static int count = 0;                // Class variable to count objects

  // Instance variables
  double radius;                       // Radius of a sphere

  double xCenter;                      // 3D coordinates
  double yCenter;                      // of the center
  double zCenter;                      // of a sphere

  // Plus the rest of the class definition...
}

You name a class using an identifier of the same sort you've been using for variables. By convention, though, class names in Java begin with a capital letter, so the class name is Sphere with a capital S. If you adopt this approach, you will be consistent with most of the code you come across. You could enter this source code and save it as the file Sphere.java. You'll be adding to this class definition and using it in a working example a little later in this chapter.

You may have noticed that in the examples in previous chapters the keyword public in this context preceded the keyword class in the first line of the class definition. The effect of the keyword public is bound up with the notion of a package containing classes, but I'll defer discussing this until a little later in this chapter when you have a better idea of what makes ...