ITEM Listener Event in Advanced Java Programming

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Item events are generated by components that present users with items to-choose from. The components that generate these events are choiceList,Checkbox, and CheckboxMenuItem. The following is the definition of the ItemEvent class.

public class ItemEvent extends AWTEvent { public static final int DESELECTED; public static final int ITEM_STATE_CHANGED; public static final int SELECTED; public ItemEvent(ItemSelectable source, int id, Object item, int stateChanged); public Object getItem(); public ItemSelectable getItemSelectable(); public int getStatechange(); public String paramString(); }

A component can process its own item events by calling enableEvents(AWTEvent.ITEM_EVENT_MASK) and providing a processItemEvent() method. alternatively, a component can delegate item events to a listener that implements the ItemListener interface:

public interface ItemListener extends EventListener { void itemStateChanged(ItemEvent ie); }

The applet listed below consists of a list component and a choice component. The List delegates its item events to the applet. The choice is a subclass that handles its own item events. Both events handlers print a message to the console.

/* =========================================================== File Name : ItemListenerTest.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="ItemListenerTest" Width=300 Height=300> </APPLET> */ public class ItemListenerTest extends Applet implements ItemListener { List lt; SelfChoice slfch; public void init() { // A list that delegates to the applet. lt = new List(5,false); lt.addItem("Chocolate"); lt.addItem("Vanilla"); lt.addItem("Strawberry"); lt.addItem("Mocha"); lt.addItem("Peppermint Swirl"); lt.addItem("Blackberry Ripple"); lt.addItem("Butterscotch"); lt.addItem("Almond"); lt.addItemListener(this); add(lt); // A choice subclass that handles its own item events slfch = new SelfChoice(); slfch.addItem("Ice Cream"); slfch.addItem("Frozen Yogurt"); slfch.addItem("Sorbet"); add(slfch); } public void itemStateChanged(ItemEvent ItmEvt) { System.out.println("New item from list:" + lt.getSelectedItem()); } } class SelfChoice extends Choice { public SelfChoice() { enableEvents(AWTEvent.ITEM_EVENT_MASK); } public void processItemEvent(ItemEvent ItmEvt) { System.out.println("New item from choice: "+ getSelectedItem()); } }

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

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

"Output of ItemListenerTest.class"

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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