Text Listener Event in Advanced Java Programming

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Text events are sent to text components(text field and text areas) when a change occurs to the text they contain. This happens when the user types something or when a program executes a method such as a setText().

The following is the definition of the TextEvent class:
public class TextEvent extends AWTEvent { public static final int TEXT_VALUE_CHANGED; public TextEvent(Object source, int id); public String paramString(); }

A text component can process its own text events by calling enableEvents(AWTEvent.TEXT_EVENT_MASK) and providing a processTextEvent() method. Alternatively, a text component can delegate text events to a listener that implements the TextListener interface:

public interface TextListener extends EventListener { public void textValueChanged(TextEvent te); }

The following applet contains two text areas: the upper one delegates text events to the applet, and the lovwer one handles its own text events. Both event handlers just print a message to the console.

/* =========================================================== File Name : TextListenerTest.java WebSite : http://javaproglang.blogspot.in/ Facebook : https://www.facebook.com/AdvanceJavaProgramming Twitter ID : https://twitter.com/AdvanceJava Created By : Bintu Chaudhary =========================================================== */ import java.applet.Applet; import java.awt.*; import java.awt.event.*; /* <APPLET Code="TextListenerTest" Width=300 Height=300> </APPLET> */ public class TextListenerTest extends Applet implements TextListener { public void init() { setLayout(new GridLayout(2,1)); // A text area that delegates to the applet TextArea ta = new TextArea(); ta.addTextListener(this); add(ta); // A text area subclass that handles its own item events SelfTextTA slfta = new SelfTextTA(); add(slfta); } public void textValueChanged(TextEvent TxtEvt) { System.out.println("UPPER get text event: " + TxtEvt); } } class SelfTextTA extends TextArea { public SelfTextTA() { enableEvents(AWTEvent.TEXT_EVENT_MASK); } public void processTextEvent(TextEvent TxtEvt) { System.out.println("LOWER get text event: " + TxtEvt); } }

The above code will be stored in the file called TextListenerTest.java, which on compilation will crate a class file called TextListenerTest.class. Now compile this file using below commands in the DOS mode:

C:\>jdk1.4\bin>javac TextListenerTest.java
C:\>jdk1.4\bin>appletviewer TextListenerTest.java

"Output of TextListenerTest.class"

Output of TextListenerTest.class in DOS mode

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Event Listener

Action Listener	Adjustment Listener	Mouse Listener
Mouse Motion Listener	Window Listener	Key Listener
Focus Listener	ITEM Listener	Text Listener