Introduction

In this chapter, we overview several of Java's capabilities for drawing two-dimensional shapes, controlling colors and controlling fonts. One of Java's initial appeals was its support for graphics that enabled programmers to visually enhance their applications. Java now contains many more sophisticated drawing capabilities as part of the Java 2D™ API. This chapter begins with an introduction to many of Java's original drawing capabilities. Next we present several of the more powerful Java 2D capabilities, such as controlling the style of lines used to draw shapes and the way shapes are filled with color and patterns. [Note: Several concepts covered in this chapter have already been covered in the optional GUI and Graphics Case Study of Chapters 310. So, some material will be repetitive if you read the case study. You do not need to read the case study to understand this chapter.]

Figure 12.1 shows a portion of the Java class hierarchy that includes several of the basic graphics classes and Java 2D API classes and interfaces covered in this chapter. Class Color contains methods and constants for manipulating colors. Class JComponent contains method paintComponent, which will be used to draw graphics on a component. Class Font contains methods and constants for manipulating fonts. Class FontMetrics contains methods for obtaining font information. Class Graphics contains methods for drawing strings, lines, rectangles and other shapes. Class Graphics2D, which extends class Graphics, is used for drawing with the Java 2D API. Class Polygon contains methods for creating polygons. The bottom half of the figure lists several classes and interfaces from the Java 2D API. Class BasicStroke helps specify the drawing characteristics of lines. Classes GradientPaint and TexturePaint help specify the characteristics for filling shapes with colors or patterns. Classes GeneralPath, Line2D, Arc2D, Ellipse2D, Rectangle2D and RoundRectangle2D represent several Java 2D shapes. [Note: We begin the chapter by discussion Java's original graphics capabilities, then move on to the Java 2D API. However, it is important to understand that the classes discussed as part of Java's original graphics capabilities are now also considered to be part of the Java 2D API.]

Figure 12.1. Classes and interfaces used in this chapter from Java's original graphics capabilities and from the Java 2D API. [Note: Class Object appears here because it is the superclass of the Java class hierarchy.]

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To begin drawing in Java, we must first understand Java's coordinate system (Fig. 12.2), which is a scheme for identifying every point on the screen. By default, the upper-left corner of a GUI component (e.g., a window) has the coordinates (0, 0). A coordinate pair is composed of an x-coordinate (the horizontal coordinate) and a y-coordinate (the vertical coordinate). The x-coordinate is the horizontal distance moving right from the left of the screen. The y-coordinate is the vertical distance moving down from the top of the screen. The x-axis describes every horizontal coordinate, and the y-axis describes every vertical coordinate.

Figure 12.2. Java coordinate system. Units are measured in pixels.

Text and shapes are displayed on the screen by specifying coordinates. The coordinates are used to indicate where graphics should be displayed on a screen. Coordinate units are measured in pixels. A pixel is a display monitor's smallest unit of resolution.

Portability Tip 12.1

Different display monitors have different resolutions (i.e., the density of the pixels varies). This can cause graphics to appear to be different sizes on different monitors or on the same monitor with different settings.