java - 我的循环出了什么问题？

Question

所以我试图通过减少行数和使用大量循环来“优化”我的代码。但这是......有问题的。

我只是想显示一堆单选按钮，但只出现了两个按钮，并且没有执行任何操作。

只是想知道是否有人可以批评我的代码并告诉这个新手他哪里出了问题。

感谢您的帮助:)

import java.awt.event.*;
import javax.swing.*;  
import javax.swing.JOptionPane;
import javax.swing.JFrame;
import javax.swing.JLabel;
import java.awt.BorderLayout;
import java.awt.Color;


public class NewGame implements ActionListener {

    private final String[] premierLeagueClubs = {"Arsenal", "Bournemouth", "Burnley", "Chelsea", "Crystal Palace",
        "Everton", "Hull City", "Leicester City", "Liverpool", "Manchester United", "Manchester City", "Middlesborough",
        "Southampton", "Stoke City", "Sunderland", "Swansea City", "Tottenham Hotspur", "Watford", "West Brom", "West Ham"};
    private final JRadioButton[] rb = new JRadioButton[20];
    JFrame f3;
    private final JButton b, quit;
    String teamName;
    JLabel label1;
    private static JPanel chooseClubPanel;

    public NewGame() {
        f3 = new JFrame("Ballon d'or");
        f3.setExtendedState(JFrame.MAXIMIZED_BOTH);
        f3.setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE);

        chooseClubPanel = new JPanel();
        f3.add(chooseClubPanel, BorderLayout.CENTER);
        chooseClubPanel.setBackground(Color.GREEN);

        label1 = new JLabel("Please choose a team");
        chooseClubPanel.add(label1);

        ButtonGroup bg = new ButtonGroup();

        int startvalueBG;
        int endvalueBG = 19;
        for (startvalueBG = 0; startvalueBG <= endvalueBG; startvalueBG++) {
            bg.add(rb[startvalueBG]);
        }

        b = new JButton("OK");
        b.addActionListener(this);
        chooseClubPanel.add(b);

        quit = new JButton("Quit");
        quit.addActionListener(this);
        chooseClubPanel.add(quit);

        int startValueAddRB;
        int endValueAddRB = 19;
        for (startValueAddRB = 0; startValueAddRB <= endValueAddRB; startValueAddRB++) {
            f3.add(rb[startValueAddRB]);
        }

        int startRB;
        int endRB = 19;

        for (startRB = 0; endRB <= 19; startRB++) {
            for (int i = 0; i < premierLeagueClubs.length; i++) {
                rb[startRB] = new JRadioButton(premierLeagueClubs[i]);
                chooseClubPanel.add(rb[i]);
            }
        }
        f3.addWindowListener(new WindowAdapter() {

            @Override
            public void windowClosing(WindowEvent e) {
                if (JOptionPane.showConfirmDialog(f3, "Are you sure ?", "Warning", JOptionPane.YES_NO_OPTION) == JOptionPane.YES_OPTION) {
                    f3.setVisible(false);
                    f3.dispose();
                } else {

                    f3.setVisible(true);
                }
            }
        });
    }

    public void setFrame(JFrame f3) {
        this.f3 = f3;
    }

    public JFrame getFrame() {

        return f3;
    }

    @Override
    public void actionPerformed(ActionEvent e) {

        int rbNumber;
        int rbNumberMax = 19;

        for (rbNumber = 0; rbNumber < rbNumberMax; rbNumber++) {
            if (rb[rbNumber].isSelected()) {
                teamName = rb[rbNumber].getText();
                f3.dispose();
                JOptionPane.showMessageDialog(f3, "You chose : " + rb[rbNumber].getText());

            }
        }

    }

}

Answer 1

那么，让我们看一下代码......

首先，您尝试将每个按钮添加到 ButtonGroup 中，但是，您实际上尚未创建任何按钮，可能会出现 NullPointerException

int startvalueBG;
int endvalueBG = 19;
for (startvalueBG = 0; startvalueBG <= endvalueBG; startvalueBG++) {
    bg.add(rb[startvalueBG]);
}

b = new JButton("OK");
b.addActionListener(this);
chooseClubPanel.add(b);

quit = new JButton("Quit");
quit.addActionListener(this);
chooseClubPanel.add(quit);

然后，您将每个按钮添加到框架中，但是，框架使用 BorderLayout，因此只有一个按钮保持可见，即您添加的最后一个按钮...

int startValueAddRB;
int endValueAddRB = 19;
for (startValueAddRB = 0; startValueAddRB <= endValueAddRB; startValueAddRB++) {
    f3.add(rb[startValueAddRB]);
}

然后，您尝试将按钮添加到 chooseClubPanel，有效地从框架中删除 ，但索引都搞乱了，您正在创建 19x19 按钮，每个俱乐部都分配给所有 19 个按钮，并且有效地被下一个俱乐部取代......!？!？

int startRB;
int endRB = 19;

for (startRB = 0; endRB <= 19; startRB++) {
    for (int i = 0; i < premierLeagueClubs.length; i++) {
        rb[startRB] = new JRadioButton(premierLeagueClubs[i]);
        chooseClubPanel.add(rb[i]);
    }
}

我们要做的第一件事是删除对框架 chooseClubPanel 的引用，它们只是妨碍并且类没有生成框架的业务，这不是它的责任.

接下来，我们将使 NewGame 成为 JPanel 并允许它 self 管理。

接下来，我们要将循环数量从 3 个减少到 1 个，并同时完成我们需要完成的所有工作

public class NewGame extends JPanel implements ActionListener {

    private final String[] premierLeagueClubs = {"Arsenal", "Bournemouth", "Burnley", "Chelsea", "Crystal Palace",
                                                                                             "Everton", "Hull City", "Leicester City", "Liverpool", "Manchester United", "Manchester City", "Middlesborough",
                                                                                             "Southampton", "Stoke City", "Sunderland", "Swansea City", "Tottenham Hotspur", "Watford", "West Brom", "West Ham"};
    private final JRadioButton[] rb = new JRadioButton[20];
    private final JButton b, quit;
    String teamName;
    JLabel label1;

    ButtonGroup bg = new ButtonGroup();

    public NewGame() {
        setBackground(Color.GREEN);

        label1 = new JLabel("Please choose a team");
        add(label1);

        for (int i = 0; i < premierLeagueClubs.length; i++) {
            rb[i] = new JRadioButton(premierLeagueClubs[i]);
            rb[i].setActionCommand(premierLeagueClubs[i]);
            bg.add(rb[i]);
            add(rb[i]);
        }

        b = new JButton("OK");
        b.addActionListener(this);
        add(b);

        quit = new JButton("Quit");
        quit.addActionListener(this);
        add(quit);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        System.out.println("You have selected " + bg.getSelection().getActionCommand());
    }

}

在某些时候您想要显示，最简单的解决方案是将其添加到您想要的任何容器，例如 JFrame

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            JFrame frame = new JFrame("Title");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.add(new NewGame());
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        }
    });
}

通常我建议查看Laying Out Components Within a Container但就你而言，我认为看看 How to Use Lists 会更实用。