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Java Programming
from the Grounds Up

Java Classes and Methods

Java utilizes the basic object technology found in C++. In a nutshell, the Java language supports the idea of data packaging, or encapsulation, through its mechanism. A Java class is an association between data elements and/or functions, much like an extended struct in C (or a C++ class). In fact, there are no structs in Java at all; the mechanism of grouping together similar elements is achieved only by creating a class. The functional members of a class are referred to as the class methods. Just as a C struct may contain other structs within it, a Java class may be built on top of another class--although only one at a time--and inherit that class's behaviors as well.

Java has its own syntax for describing methods and classes. It supports public class members, which are visible outside the class; protected members, which are visible only within the class and its subclasses; and private members, which are only visible within that particular class. Java supports abstract (virtual) classes, in which some or all of the member functions are declared, but not defined--they have no function body, so that only subclasses which fully define those functions may be used.

If you have some experience with C++ programming, many of these concepts will be familiar to you. However, there are several striking differences between C++ and Java. Much of the implicit behavior that C++ takes for granted is absent in Java. For example, there are no default constructors: a Java program must explicitly call the operator new to create a new instance of a class. In addition, arithmetic operators such as "+" or "= =" may not overload in Java. There is no way for the programmer to extend the behavior of "+" beyond what Java provides intrinsically. Another highly visible departure from C and C++ is that there are no pointers (and logically, no pointer arithmetic) in Java.

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Mark Reynolds is a network protocol designer, Java programmer, computer animator, and fanatic mountaineer. He currently consults to Adaptive Optics Associates, a United Technologies company.

Reprinted from Web Developer® magazine, Vol. 2 No.1 Spring 1996 (c) 1996 internet.com Corporation. All rights reserved.

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