J2ME in a Nutshell

The High-Level User Interface API

A MIDlet written using the high-level API typically consists of one or more screens built using the Form, List, or TextBox classes, together with a set of Commands that allow the user to tell the MIDlet what actions to perform and how to navigate from screen to screen. Let’s start our examination of the high-level API by creating a simple MIDlet with a single screen containing a TextBox.

A TextBox Example

TextBox is a component used to display and modify text. Since it is derived from Screen, TextBox occupies the entire screen of the device and therefore can accomodate relatively large amounts of text spread over several lines. Most of the API provided by TextBox is identical to that of a similar component called TextField, which is covered in detail in Section 4.2.9, later in this chapter. In this example, we use only the features that TextBox inherits from Screen (and which are not available to TextField, because it is not derived from Screen). The code for this example is shown in Example 4-1.

Example 4-1. Creating and Using a TextBox

package ora.ch4; import java.io.InputStream; import java.io.InputStreamReader; import java.io.IOException; import javax.microedition.lcdui.Display; import javax.microedition.lcdui.TextBox; import javax.microedition.lcdui.TextField; import javax.microedition.lcdui.Ticker; import javax.microedition.midlet.MIDlet; public class TextBoxMIDlet extends MIDlet { // Maximum size of the text in the TextBox private static ...