我希望在第一个组合框中选择的城市不会出现在第二个组合框中

Question

如果我选择一个城市 FROM:JComboBox 那么它不应该出现在 TO: 组合框中。如何编码此动作侦听器的ActionListener？

Screenshot

代码：

public class CityFromTo {

    public static void main(String[] args) {
        
        String[] cFrom = {"Choose", "Istanbul", "New York", "London", "Milano", "Tokyo", "Paris", "Moscow", "Elâzığ"};
        String[] cTo = {"Choose", "Istanbul", "New York", "London", "Milano", "Tokyo", "Paris", "Moscow", "Elâzığ"};
        
        JLabel from = new JLabel("FROM : ");
        JLabel to = new JLabel("   TO : ");

        JComboBox comboFrom = new JComboBox(cFrom);
        JComboBox comboTo = new JComboBox(cTo);
        
        JFrame frame = new JFrame();
        frame.setLayout(new FlowLayout());

        frame.add(from);
        frame.add(comboFrom);
        frame.add(to);
        frame.add(comboTo);
        
        frame.setSize(400, 350);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

Answer 1

我重新编写了您的代码以摆脱静态。您只需要一份城市列表作为起点和终点JComboBoxes。

您使用ActionListener 来监听来自JComboBox 的变化，并从JComboBox 中删除城市。我们通过删除所有城市并将它们重新添加来删除城市，一次一个。这允许用户改变他对来自城市的想法。

这是完整的可运行代码。

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class CityFromTo implements Runnable {
    
    public static void main(String[] args) {
       SwingUtilities.invokeLater(new CityFromTo());
    }
    
    private JComboBox<String> comboFrom;
    private JComboBox<String> comboTo;
    
    private String[] cities = {"Choose", "Istanbul", "New York", "London", 
            "Milano", "Tokyo", "Paris", "Moscow", "Elâzığ"};

    @Override
    public void run() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        frame.add(createMainPanel(), BorderLayout.CENTER);
        
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
    
    private JPanel createMainPanel() {
        JPanel panel = new JPanel(new FlowLayout());
        panel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
        panel.setPreferredSize(new Dimension(400, 350));
        
        JLabel from = new JLabel("FROM : ");
        panel.add(from);
        
        comboFrom = new JComboBox<>(cities);
        comboFrom.addActionListener(new FromListener());
        panel.add(comboFrom);
        
        JLabel to = new JLabel("   TO : ");
        panel.add(to);
        
        comboTo = new JComboBox<>(cities);
        panel.add(comboTo);
        
        return panel;
    }
    
    public class FromListener implements ActionListener {

        @Override
        public void actionPerformed(ActionEvent event) {
            String city = (String) comboFrom.getSelectedItem();
            comboTo.removeAllItems();
            for (String s : cities) {
                if (!s.equals(city)) {
                    comboTo.addItem(s);
                }
            }
        }
        
    }

}