Source

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

public class AnAppletWithCheckboxes extends Applet implements ItemListener {
    public void init() {
        setLayout(new GridLayout(1, 0));

        CheckboxGroup dinnerType = new CheckboxGroup();
        standard = new Checkbox("standard", dinnerType, false);
        standard.addItemListener(this);
        deluxe = new Checkbox("deluxe", dinnerType, true);
        deluxe.addItemListener(this);

        CheckboxGroup appetizers = new CheckboxGroup();
        crepe = new Checkbox("crepe", appetizers, false);
        crepe.addItemListener(this);
        quiche = new Checkbox("quiche", appetizers, false);
        quiche.addItemListener(this);
        dumpling = new Checkbox("dumpling", appetizers, false);
        dumpling.addItemListener(this);

        CheckboxGroup soupOrSalad = new CheckboxGroup();

        soup = new Checkbox("Soup", soupOrSalad, false);
        soup.addItemListener(this);

        CheckboxGroup soups = new CheckboxGroup();
        cream = new Checkbox("cream", soups, false);
        cream.addItemListener(this);
        broth = new Checkbox("broth", soups, false);
        broth.addItemListener(this);
        gumbo = new Checkbox("gumbo", soups, false);
        gumbo.addItemListener(this);

        salad = new Checkbox("Salad", soupOrSalad, false);
        salad.addItemListener(this);

        CheckboxGroup salads = new CheckboxGroup();
        tossed = new Checkbox("tossed", salads, false);
        tossed.addItemListener(this);
        caesar = new Checkbox("caesar", salads, false);
        caesar.addItemListener(this);
        croutons = new Checkbox("croutons");
        croutons.addItemListener(this);
        lite = new Checkbox("lite dressing");
        lite.addItemListener(this);


        CheckboxGroup entrees = new CheckboxGroup();
        chicken = new Checkbox("chicken", entrees, false);
        chicken.addItemListener(this);
        beef = new Checkbox("beef", entrees, false);
        beef.addItemListener(this);
        lamb = new Checkbox("lamb", entrees, false);
        lamb.addItemListener(this);
        fish = new Checkbox("fish", entrees, false);
        fish.addItemListener(this);

        CheckboxGroup deserts = new CheckboxGroup();
        pie = new Checkbox("pie", deserts, false);
        pie.addItemListener(this);
        fruit = new Checkbox("fruit", deserts, false);
        fruit.addItemListener(this);
        sherbet = new Checkbox("sherbet", deserts, false);
        sherbet.addItemListener(this);


        setLayout(new GridLayout(0, 1));

        Panel p = new Panel();
        add(p);
        p.add(standard);
        p.add(deluxe);

        appetizerPanel = new Panel();
        add(appetizerPanel);
        appetizerPanel.add(new Label("Appetizer"));
        appetizerPanel.add(crepe);
        appetizerPanel.add(quiche);
        appetizerPanel.add(dumpling);

        soupPanel = new Panel();
        add(soupPanel);
        soupPanel.add(soup);
        soupPanel.add(cream);
        soupPanel.add(broth);
        soupPanel.add(gumbo);

        saladPanel = new Panel();
        add(saladPanel);
        saladPanel.add(salad);
        saladPanel.add(tossed);
        saladPanel.add(caesar);
        saladPanel.add(croutons);
        saladPanel.add(lite);


        entreePanel = new Panel();
        add(entreePanel);
        entreePanel.add(new Label("Entree"));
        entreePanel.add(chicken);
        entreePanel.add(beef);
        entreePanel.add(lamb);
        entreePanel.add(fish);

        desertPanel = new Panel();
        add(desertPanel);
        desertPanel.add(new Label("Desert"));
        desertPanel.add(pie);
        desertPanel.add(fruit);
        desertPanel.add(sherbet);
	}

    public void itemStateChanged(ItemEvent e) {
        if (e.getSource() == standard || e.getSource() == deluxe)
            handleDinnerType((Checkbox)e.getSource());
        else if (e.getSource() == soup || e.getSource() == salad)
            handleSoupSaladChoice((Checkbox)e.getSource());
    }

    void handleDinnerType(Checkbox selectedType) {
        boolean enabled;
        if (selectedType == standard)
            enabled = false;
        else
            enabled = true;
        pie.setEnabled(enabled);
        fruit.setEnabled(enabled);
        sherbet.setEnabled(enabled);
        cream.setEnabled(enabled);
        broth.setEnabled(enabled);
        gumbo.setEnabled(enabled);
        tossed.setEnabled(enabled);
        caesar.setEnabled(enabled);
        croutons.setEnabled(enabled);
        lite.setEnabled(enabled);

    }

    void handleSoupSaladChoice(Checkbox selectedCourse) {
        boolean soupEnabled, saladEnabled;
        if (selectedCourse == soup) {
            soupEnabled = true;
            saladEnabled = false;
        }
        else {
            soupEnabled = false;
            saladEnabled = true;
        }
        cream.setEnabled(soupEnabled);
        broth.setEnabled(soupEnabled);
        gumbo.setEnabled(soupEnabled);

        tossed.setEnabled(saladEnabled);
        caesar.setEnabled(saladEnabled);
        croutons.setEnabled(saladEnabled);
        lite.setEnabled(saladEnabled);
    }

    Panel
        appetizerPanel, soupPanel, saladPanel, entreePanel, desertPanel;

    Checkbox
        standard, deluxe,
        soup, salad,
        crepe, quiche, dumpling,
        cream, broth, gumbo,
        tossed, caesar,
        croutons, lite,
        chicken, beef, lamb, fish,
        pie, fruit, sherbet;
}

Notes

This tutorial is somewhat different than the previous one-- it is more than a simple bare-boned demonstration of a new AWT GUI component. While it does introduce a new component-- the Checkbox, it also illustrates how the programmer can introduce more complex logic into the event handlers in order to enhance the behavior of the interface.

The Checkbox Component

The Checkbox component allows the user to check off one or more choices from a fixed set of choices. Checkbox objects may either exist in isolation from each other (as in the croutons/lite dressing) choices, or they may be created as belonging to a CheckboxGroup object, in which case they are mutually exclusive (only one box in the group may be selected)-- in which case they are often called radio buttons.

This Applet's Behavior

• This applet presents the user with an menu that changes interactively as the user makes various choices
• The basic rules are:
  • A standard dinner consists of an appetizer and an entree
  • A deluxe dinner consists of an appetizer, soup OR salad (not both), and entree, and a desert

The Logic and Structure of the Applet

• You can choose either a standard or a deluxe dinner, but not both
• Each category (e.g., appetizers) allows you to choose only one item
• The salad category allows the user to choose croutons and/or lite dressing

• Selecting the standard/deluxe dinner type disables/enables the soup, salad, and desert options
• For a delixe dinner, selecting the soup option disables the salad option and vice versa.

Things to Do

• Examine the Checkbox and CheckboxGroup classes-- is the API beginning to make sense to you?