Java AWT Reference

5

Components

In this chapter:

• Component
• Labels
• Buttons
• A Simple Calculator
• Canvas
• Creating Your Own Component
• Cursor

This chapter introduces the generic graphical widget used within the AWT package, Component, along with a trio of specific components: Label, Button, and Canvas. It also covers the Cursor class, new to Java 1.1. (Cursor support was previously part of the Frame class.) Although many objects within AWT don't subclass Component, and though you will never create an instance of Component, anything that provides screen-based user interaction and relies on the system for its layout will be a child of Component. As a subclass of Component, each child inherits a common set of methods and an API for dealing with the different events (i.e., mouse click, keyboard input) that occur within your Java programs.

After discussing the methods in Component classes, this chapter goes into detail about two specific components, Label and Button. A Label is a widget that contains descriptive text, usually next to an input field. A Button is a basic mechanism that lets the user signal the desire to perform an action. You will learn about the Canvas object and how to use a Canvas to create your own component. Finally, we cover the Cursor class, which lets you change the cursor over a Component.

Before going into the mechanics of the Component class, it's necessary to say a little about the relationship between components and containers. A Container is also a component with the ability ...