Text

There are two user interface components that enable a person to type in text. One is a "TextField" (a single line of text) and one is a "TextArea" (multiple lines of text). Experiment with the applet below to see what it does. Then proceed to understand the code that generates the applet.

An applet would be displayed here if your browser supported Java.

For an applet to use a "TextField" or a "TextArea" it must implement a "TextListener" interface. Consulting the event handling reference, a "TextListener" interface requires a "textValueChanged" method to be implemented.

In the example below, a "TextField" named "nameField" and a "TextArea" named "commentArea" are used. The "init" method begins by activating the null layout manager and setting the value of "message" to the empty string. It then instantiates a "TextField", locates and sizes it with the "setBounds" method, adds it to the display, and adds a listener that will respond to various text events.

The "init" method now instantiates a "TextArea", sets its size and location, adds it to the display, and adds a listener for it. Notice that when the null layout manager is being used, we will always have to set the width and height of a component (unless we want it to default to 0 by 0) and its location (unless we want it to default to the upper left corner of the display area).

In the "textValueChanged" method, a "getText" method is called to read the text that is currently in the "nameField". Then "repaint" is called to update what is being displayed.

The "paint" method is fairly straight-forward. It provides a text label for both "nameField" and "commentArea". Then it checks to see what the current contents of the "nameField" is. If it isn't the empty string, a greeting message is displayed in the middle of the top of the display area.

import java.awt.*;
import java.awt.event.*;
import java.applet.*;

public class Example extends Applet implements TextListener
{
	public void init()
	{	
		setLayout(null);

		message = "";

		nameField = new TextField();
		nameField.setBounds(100, 100, 100, 30);
		add(nameField);
		nameField.addTextListener(this);

		commentArea = new TextArea();
		commentArea.setBounds(100, 200, 100, 100);
		add(commentArea);
		commentArea.addTextListener(this);

	public void textValueChanged(TextEvent evt)
	{
		message = nameField.getText();
		repaint();
	}

	public void paint (Graphics g)
	{

		g.drawString("Name: ", 100, 90);
		g.drawString("Comments: ", 100, 190);

		if (! message.equals(""))
			g.drawString("Hi " + message, 100, 50);
	}

	private TextField nameField;
	private TextArea commentArea;

	private String message;