Java The Complete Reference, Seventh Edition

Chapter 24: Using AWT Controls, Layout Managers, and Menus 751

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

public class CheckboxDemo2 extends Applet {
MyCheckbox myCheckbox1, myCheckbox2, myCheckbox3;
public void init() {
myCheckbox1 = new MyCheckbox("Item 1");
add(myCheckbox1);
myCheckbox2 = new MyCheckbox("Item 2");
add(myCheckbox2);
myCheckbox3 = new MyCheckbox("Item 3");
add(myCheckbox3);
}
class MyCheckbox extends Checkbox {
public MyCheckbox(String label) {
super(label);
enableEvents(AWTEvent.ITEM_EVENT_MASK);
}
protected void processItemEvent(ItemEvent ie) {
showStatus("Checkbox name/state: " + getLabel() +
"/" + getState());
super.processItemEvent(ie);
}
}
}

Extending a Check Box Group

The following program reworks the preceding check box example so that the check boxes
form a check box group. Thus, only one of the check boxes may be selected at any time.

/*

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

public class CheckboxGroupDemo2 extends Applet {
CheckboxGroup cbg;
MyCheckbox myCheckbox1, myCheckbox2, myCheckbox3;
public void init() {
cbg = new CheckboxGroup();
myCheckbox1 = new MyCheckbox("Item 1", cbg, true);
add(myCheckbox1);
myCheckbox2 = new MyCheckbox("Item 2", cbg, false);
add(myCheckbox2);
myCheckbox3 = new MyCheckbox("Item 3", cbg, false);
add(myCheckbox3);
}
class MyCheckbox extends Checkbox {
public MyCheckbox(String label, CheckboxGroup cbg,
boolean flag) {
super(label, cbg, flag);