Syntax for Writing Your Own Class

Syntactically, a class has two basic parts:

1. Attributes - the values tied to an object of that class. For instance, an object of class Point has an x coordinate and a y coordinate. The attributes of an object are stored in instance variables, which are also sometimes called fields.

   These are coded as declarations, and belong just after the opening curly brace that comes right after the public class line.

2. Behaviors - the ways in which an object of that class can behave or be manipulated. The behaviors of an object are defined by the constuctors and other methods that belong to that class.

Basic Syntax

The basic syntax for a Java class is:

public class ClassName extends ParentClass
{
// declaration of instance variable(s)

private Class   instanceVariable;
...

public returnType methodName(class arg1, ...)
{
    statement;
    ...
    return x;   // where x is of type returnType
}
}

More notes:

• You may put multiple classes in a single source file, but only the main one, the one that matches the filename, should be declared as public.

• If you create a class that does not specify its superclass with the extends keyword, it automatically is defined as a subclass of the Object class (this has more relevance when we discuss inheritance).

• The instance variables are also called attributes, data members, member variables, or fields.

• The section that creates these variables can only consist of declarations.

• To create an object of your new class, the programmer must call a constructor. (How is this done?)

• To call a method in the class, the programmer should use dot-notation. (How is this done?)

  Exception to using dot-notation:

  To call a method in the same class, do not use dot-notation, just call the method directly.

• For now, write your classes in the same directory and there is no need to import them.