Chapter 12. Graphics

Java 1.0 and 1.1 provided rudimentary graphics capabilities through the java.awt.Graphics class and associated classes, such as java.awt.Color and java.awt.Font. In Java 1.2 and later, the Java 2D API provides state-of-the-art, two-dimensional graphics facilities using the java.awt.Graphics2D class (a subclass of Graphics) and associated classes, such as java.awt.BasicStroke, java.awt.GradientPaint, java.awt.TexturePaint, java.awt.AffineTransform, and java.awt.AlphaComposite.

This chapter demonstrates using all these classes; it shows how you can draw graphics with and without the Java 2D API. The key class for all graphics operations is Graphics (or in the Java 2D API, its subclass, Graphics2D). The purpose of this class is threefold:

It defines the drawing surface

A Graphics object can represent the on-screen drawing area within an AWT (or Swing) component. It can also represent an off-screen image you can draw into or a piece of paper to be printed on a printer.

It defines drawing methods

All primitive graphics operations, such as drawing lines, filling shapes, and displaying text, are performed using methods of the Graphics class.

It defines attributes used by the drawing methods

Various methods of the Graphics class can set the font, color, clipping region, and other attributes used when performing graphics operations, such as drawing lines, filling shapes, and displaying text. The values of these graphical attributes are often instances of AWT classes, such as Color, Font, Stroke, AffineTransform, and so on.

The graphics capabilities of Java are intimately wed with the AWT. As such, the Graphics and Graphics2D classes are part of the java.awt package, as are all the associated classes that define graphical attributes. As we discussed in Chapter 11, the central class of the AWT is java.awt.Component. Component is the basic building block of all graphical user interfaces in Java. A Graphics object represents a drawing surface, but Java doesn't allow you to draw directly to the computer screen. Instead, it restricts you to drawing within the confines of a Component, using a Graphics object that represents the drawing surface of that component. Thus, to do graphics in Java, you must have a Component (or a java.applet.Applet, a Component subclass) to draw into. Drawing is usually done by subclassing a specific component and defining a paint( ) method (or a paintComponent( ) method, for Swing components). The examples in this chapter have been structured to focus on the mechanics of drawing, rather than the mechanics of GUI creation, but you will still see some code that handles GUI-related tasks.