/*File Event35.java, Copyright 1998, R.G.Baldwin Illustrates Item events. This program creates three radio buttons in a group.  When any of the three buttons is selected, the other two are automatically deselected. An ItemListener object is registered on all three buttons. When a button is selected, an ItemEvent occurs. The program also creates an ordinary checkbox. The ItemListener object is also registered on the checkbox.   When the checkbox is either selected or deselected an  ItemEvent occurs. When an ItemEvent occurs, the itemStateChanged() method of the ItemListener object is invoked.  Code in this method invokes methods of the ItemEvent object received as a  parameter to display  1. the label of the item,  2. the "StateChange" of the item, and  3. the new state of the item. The labels on the three buttons are AButton, BButton, and CButton.  The label on the checkbox is Check Box. The following is the output produced by selecting BButton, selecting Check Box, and then deselecting Check Box, in  that order. Item: BButton State Change: 1 State: true Item: Check Box State Change: 1 State: true Item: Check Box State Change: 2 State: false Several things are worthy of note here.  First, a state change from deselected to selected produces a state  change value of 1, while a change from selected to deselected produces a value of 2.  So far, I have found no documentation to explain the significance of these values. Second, the checkbox generates an item event when it is selected, and also when it is deselected. Third, whenever one of the radio buttons is selected, the others are automatically deselected.  However, only one item event results, and it is attributed to the button that is selected.  Automatic deselection of the other buttons does not cause them to generate item events. Tested using JDK1.1.6 under Win95. **********************************************************/ import java.awt.*; import java.awt.event.*; import java.util.*; //=======================================================// public class Event35 extends Frame implements ItemListener{   public static void main(String[] args){     new Event35();   }//end main   //-----------------------------------------------------//   Event35(){//constructor     //Create a CheckboxGroup object     CheckboxGroup cbGrp = new CheckboxGroup();     //Create three radio buttons in the group     Checkbox aButton = new Checkbox("AButton",true, cbGrp);     Checkbox bButton = new Checkbox("BButton",false,cbGrp);     Checkbox cButton = new Checkbox("CButton",false,cbGrp);          //Register item listener object on each radio button     aButton.addItemListener(this);     bButton.addItemListener(this);     cButton.addItemListener(this);          //Create an ordinary checkbox and register the item     // listener on it.     Checkbox theCheckbox = new Checkbox("Check Box");     theCheckbox.addItemListener(this);          //Add the radio buttons and the checkbox to the Frame     this.add(aButton);     this.add(bButton);     this.add(cButton);     this.add(theCheckbox);     //Adjust Frame parameters and make it visible     this.setLayout(new FlowLayout());     this.setSize(350,100);     this.setTitle("Copyright 1998, R.G.Baldwin");     this.setVisible(true);          // Anonymous inner class to terminate program.     addWindowListener(new WindowAdapter() {       public void windowClosing(WindowEvent e) {         System.exit(0);}});//end WindowListener   }//end constructor   //-----------------------------------------------------//     //Define the method of the ItemListener interface   public void itemStateChanged(ItemEvent e){     System.out.println("Item: " + e.getItem());     System.out.println("State Change: "                                       + e.getStateChange());     //Note the cast in the following statement         System.out.println("State: "                     + ((Checkbox)e.getSource()).getState());     System.out.println();//blank line   }//end itemStateChanged() }//end class Event35 definition //=======================================================//