复选框项侦听器逻辑，用于订购披萨

Question

基本上这个简单的程序所做的是单击按钮时显示摘要，有三个用于比萨饼尺寸的单选按钮，以及三个用于浇头的复选框。我遇到的问题是，当用户第一次单击顶部时，然后单击按钮并在 MessageDialog 中显示适当的摘要后，当用户想要没有浇头时，它不会显示"未选择浇头"

import java.applet.Applet;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.*;
import javax.swing.*;
public class PizzaOrdering extends Applet implements ActionListener, ItemListener {
    Button btnOk = new Button("OK");
    CheckboxGroup cbgSize = new CheckboxGroup();
    Checkbox chkSmall = new Checkbox("Small", cbgSize, false);
    Checkbox chkMedium = new Checkbox("Medium", cbgSize, false);
    Checkbox chkLarge = new Checkbox("Large", cbgSize, false);
    Checkbox chkPep = new Checkbox("Pepperoni");
    Checkbox chkMush = new Checkbox("Mushroom");
    Checkbox chkAnch = new Checkbox("Anchiovies");
    String pizza = "";
    String topping1 = "";
    String topping2 = "";
    String topping3 = "";
    String others = "with no toppings";
    Label lbl1 = new Label("Size");
    Label lbl2 = new Label("Toppings");
    Label spacer = new Label("                                                ");
    Label spacer2 = new Label("                                                ");
    @Override
    public void init() {
        resize(250, 150);
        add(lbl1);
        add(spacer);
        add(chkSmall);
        add(chkMedium);
        add(chkLarge);
        add(lbl2);
        add(spacer2);
        add(chkPep);
        add(chkMush);
        add(chkAnch);
        add(btnOk);
        chkAnch.addItemListener(this);
        chkPep.addItemListener(this);
        chkMush.addItemListener(this);
        btnOk.addActionListener(this);
    }
    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == btnOk) {
            if (cbgSize.getSelectedCheckbox() == chkSmall) {
                pizza = "Small";
            }
            if (cbgSize.getSelectedCheckbox() == chkMedium) {
                pizza = "Medium";
            }
            if (cbgSize.getSelectedCheckbox() == chkLarge) {
                pizza = "Large";
            }
            JOptionPane.showMessageDialog(btnOk, "You ordered a " + 
                    pizza + " pizza " + others, "Your Order", WIDTH);
        }
    }
    @Override
    public void itemStateChanged(ItemEvent ex) {
        boolean state1 = false;
        boolean state2 = false;
        boolean state3 = false;
        if (ex.getItemSelectable() == chkMush) {
            state1 = chkMush.getState();
            if (state1 == true) {
                topping1 = "Mushroom";
            } else if (state1 == false) {
                topping1 = "";
                if (state2 == false && state3 == false) {
                    others = "with no toppings";
                }
            }
        }
        if (ex.getItemSelectable() == chkPep) {
            state2 = chkPep.getState();
            if (state2 == true) {
                topping2 = "Pepperoni";
            } else if (state2 == false) {
                topping2 = "";
                if (state1 == false && state3 == false) {
                    others = "with no toppings";
                }
            }
        }
        if (ex.getItemSelectable() == chkAnch) {
            state3 = chkAnch.getState();
            if (state3 == true) {
                topping3 = "Anchiovies";
            } else if (state3 == false) {
                topping3 = "";
                if (state1 == false && state2 == false) {
                    others = "with no toppings";
                }
            }
        }
        others = " with the following topping:" + 
                topping1 + " " + topping2 + " " + topping3;
    }
}

Answer 1

当用户不选中或取消选中任何复选框时，甚至不会调用 itemStateChanged 方法。因此，默认情况下显示"未选择浇头"标签，并在选择某些浇头时将其隐藏或删除在itemStatechanged方法中。您可以在itemStateChanged方法中使用静态 int 字段"count"，并在每次选择的顶部时递增它，并在每个取消选择的顶部时递减。

这样，对于每次取消选择，将计数减少 1 并检查计数，如果为零，只需设置该标签，"未选择顶部"可见或重新出现。

Answer 2

安排您的流程，使其无法

在披萨本身之前选择浇头（在提交信息时设定条件）。默认情况下，消息是"未选择顶部"，当他选择顶部时，您将新的顶部附加到消息的新文本中。

我建议您阅读有关装饰器设计模式（http://en.wikipedia.org/wiki/Decorator_pattern）的信息，这对您的应用程序非常有帮助。