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为什么我的组合框不执行我在 ItemListener 中声明的内容？当我单击组合框中的一个项目时，程序挂起我需要关闭整个 BlueJ。请看看我的代码有什么问题

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;

public class HulaHoops {

private Scanner inp = new Scanner(System.in);

public static void main(String[]args) {
    EventQueue.invokeLater(new Runnable()
    {
        @Override
        public void run()
        {
            new HulaHoops();
        }
    });
}

public HulaHoops() {
    JFrame frame = new JFrame();
    JPanel panel = new JPanel();
    String choices[] = {"Shoes","Comb","Ball"};
    JComboBox combo = new JComboBox(choices);
    combo.setBackground(Color.gray);
    combo.setForeground(Color.red);
    panel.add(combo);
    frame.add(panel);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(300,100);
    frame.setVisible(true);


    combo.addItemListener(new ItemListener () {
        @Override
        public void itemStateChanged(ItemEvent e)
        {
            String item = (String)e.getItem();
            if (e.getStateChange () == ItemEvent.SELECTED)
            {
                System.out.println("You chose " +item);
                    if (item == "Shoes")
                    {
                        System.out.println("Enter quantity: ");
                        int bilang = inp.nextInt();
                        int total = bilang * 99;
                        String order = bilang + " " + "Shoes " + "     " + total;
                        System.out.print("" + order);
                    }

                    else if (item == "Comb")
                    {
                        System.out.println("Enter quantity: ");
                        int bilang = inp.nextInt();
                        int total1 = bilang * 99;
                        String order1 = bilang + " " + "Comb " + "     " + total1;
                        System.out.print("" + order1);
                    }

                    else if (item == "Ball")
                    {
                        System.out.println("Enter quantity: ");
                        int bilang = inp.nextInt();
                        int total2 = bilang * 99;
                        String order2 = bilang + " " + "Ball " + "     " + total2;
                        System.out.print("" + order2);
                    }
            }

        }
    });
}

}

4

2 回答 2

3

问题是您正在阻止EDT呼叫Scanner#nextInt等待来自System.in您的输入ItemListener：

int bilang = inp.nextInt();

不要Scanner用于读取 Swing 应用程序中的用户输入。这只会阻止EDT直到控制台窗口中提供数据。有许多方法可以读取输入，例如使用JOptionPane#showInputDialog. 有关此选项的更多信息，请参阅如何制作对话框。

Aside from this, use .equals when comparing String content rather than the == operator. The latter compares Object references.

于 2013-03-06T17:09:58.817 回答
1

The basic mistake that you are doing is comparing the two String objects using == operator.
You should use the following conditions instead:

if (item .equals("Shoes"))
if (item .equals("Comb"))
if (item .equals("Ball"))

As a short demo of JOptionPane.. I am putting here the changed version of your code...I hope it will help you to understand how to handle such situation properly...

    //combo box, the program hangs I need to close the entire BlueJ. Please take a look what is wrong in my code
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;

public class HulaHoops  {

private Scanner inp = new Scanner(System.in);

public static void main(String[]args) {
    EventQueue.invokeLater(new Runnable()
    {
        @Override
        public void run()
        {
            new HulaHoops();
        }
    });
}

public HulaHoops() {
    JFrame frame = new JFrame();
    JPanel panel = new JPanel();
    String choices[] = {"Shoes","Comb","Ball"};
    JComboBox combo = new JComboBox(choices);
    combo.setBackground(Color.gray);
    combo.setForeground(Color.red);
    panel.add(combo);
    frame.add(panel);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(300,100);
    frame.setVisible(true);


    combo.addItemListener(new ItemListener () {
        @Override
        public void itemStateChanged(ItemEvent e)
        {
            String item = (String)e.getItem();
            if (e.getStateChange () == ItemEvent.SELECTED)
            {
                System.out.println("You chose " +item);
                    if (item.equals("Comb"))
                    {
            Object val = JOptionPane.showInputDialog("Please input quantity of comb"); 
            System.out.println(val);

                        Integer bilang= Integer.valueOf((String)val);
                        int total = bilang * 99;
                        String order = bilang + " " + "Shoes " + "     " + total;
                        System.out.print("" + order);
                    }


            }
    }
    });
    }
}
于 2013-03-06T17:11:21.860 回答