ON a visit to Java in 1971 I stayed with a cultured and musical family. The father listened for hours to gamelan music on the radio, and extolled its subtlety and power. Among the many beautiful ways he found to describe it, the most memorable was ‘like raindrops falling from leaves after a shower’. Writing in 1937, the Dutch author Leonhard Huizinga gave a similarly poetic description: ‘There are only two things one can compare it with: moonlight, and running water. It is pure and mysterious like moonlight; it is always the same and yet always changing, like running water.’ The aquatic metaphor common to both descriptions is not far-fetched, as at least one sound in the gamelan actually has an aquatic origin. One of the drums derives its name, and many of the sounds it produces, from ciblon, a game in which children slap the surface of water.

Introduction

Java's graphics capability has always been a leading feature of the language. The Java designers clearly expected the graphical user interface (GUI) to dominate interactions with Java programs on all but the smallest platforms. Java appeared at the start of the Internet boom and applets were expected to bring interactivity to the browser. Many thought that Java would also quickly become popular for standalone client applications on platforms with graphical operating systems.

In Java 1.0, however, the graphical elements provided for workable interfaces but they appeared crude compared to platform-specific graphics developed with other languages. The goal of portability had led to a lowest common denominator approach that was not very pretty. This became one of the main stumbling blocks that prevented Java from becoming a popular language for desktop applications.

However, with the inclusion of the Swing packages in version 1.2, Java graphics took a huge leap forward in visual appeal and in the breadth and depth of its features. With subsequent versions, Java graphics continued to improve and now compares quite well with that available with any other programming language and still provides for relatively easy portability.

In this chapter we introduce Java graphics starting with a quick overview of the Abstract Windowing Toolkit from Java 1.0. We then look at the Java Foundation Classes system, also known as “Swing,” in some detail. We wait until Chapter 7 to discuss how to bring interactivity to the user interface.

OBJECTIVES

In this chapter you will study:

• Java program structure;

• Writing class programs;

• Writing Java comments;

• Naming rules & conventions;

• Calling methods;

• Creating objects; and

• Working with subclasses.

The purpose of this chapter is to introduce you to the structure of Java programs. You will see how to write and execute simple Java programs. By working with real functioning programs, instead of just code segments, you will quickly learn the major structural differences between COBOL and Java.

This chapter begins with a program that models the Customer class from the Community National Bank system introduced in Chapter 2. This program is used to illustrate Java program structure.

We will show you how to write Java comments and review the simple rules for naming variables, methods, classes, and programs. We will also explain the Java coding conventions and style guidelines that will greatly improve the readability of your programs.

We will then execute methods in the customer class program to show how objects are created and to demonstrate calling methods. We will conclude the chapter by developing programs for the account and checking account classes to illustrate working with subclasses.

This chapter assumes you understand the following:

COBOL:

COBOL program structure

Column restrictions—area A and B

Continuation column 7

Comments and remarks

Uses of periods, commas, parentheses, spaces

Scope terminators

Rules for programmer-supplied names

Java:

OO concepts (Chapter 2)

A CLASS PROGRAM

Chapter 2 introduced object-oriented concepts and described classes and objects.