java - getActionCommand在代码中不起作用(观看教程系列)

Question

我正在看mybringback的youtube教程系列。 (该系列的第38个视频)。在代码的最底部，我有e.getactioncommand。当我单击单选按钮时，我希望它在文本字段中说些什么。例如，当我按下单选按钮1时，在文本字段中应该说“您选择了单选按钮1”。我完全按照本教程进行操作，但无法弄清楚出了什么问题。

我也有司机课。我没有在这里发布。

这是视频https://www.youtube.com/watch?v=pjS_IiNp008&list=SPDAA5DE54FB5215EC

      package ActionCommandnActionListeners;

      import java.awt.BorderLayout;
      import java.awt.GridBagConstraints;
        import java.awt.GridBagLayout;
        import java.awt.Insets;
        import java.awt.Label;
        import java.awt.event.ActionEvent;
         import java.awt.event.ActionListener;

           import javax.swing.ButtonGroup;
       import javax.swing.JButton;
       import javax.swing.JCheckBox;
       import javax.swing.JFrame;
       import javax.swing.JLabel;
        import javax.swing.JOptionPane;
      import javax.swing.JPanel;
      import javax.swing.JRadioButton;
      import javax.swing.JTextArea;
      import javax.swing.JTextField;







    public class FirstWindow extends JFrame implements ActionListener {
private static final long serialVersionUID = 1L;

String s;
JCheckBox cb, cb2;
JTextField textField;
JLabel label;
JRadioButton b1, b2, b3, b4;
ButtonGroup group;
JTextArea tb;

public FirstWindow() {
    super("Your Computer is very special");

    setSize(600, 400);
    setDefaultCloseOperation(EXIT_ON_CLOSE);

    JPanel p = new JPanel();
    JPanel p2 = new JPanel();
    JPanel p3 = new JPanel(new GridBagLayout());
    JPanel p4 = new JPanel();

    b1 = new JRadioButton("Choice 1");
    b1.setActionCommand("you selected num1");
    b1.addActionListener(this);

    b2 = new JRadioButton("Choice 2");
    b2.setActionCommand("you selected num2");
    b2.addActionListener(this);

    b3 = new JRadioButton("Choice 3");
    b3.setActionCommand("you selected num3");
    b3.addActionListener(this);

    b4 = new JRadioButton("Choice 4");
    b4.setActionCommand("you selected num4");
    b4.addActionListener(this);

    group = new ButtonGroup();
    group.add(b1);
    group.add(b2);
    group.add(b3);
    group.add(b4);

    p4.add(b1);
    p4.add(b2);
    p4.add(b3);
    p4.add(b4);

    JButton b = new JButton("Button 1");
    JButton c = new JButton("Button 2");

    p.add(b);
    p.add(c);

    cb = new JCheckBox("Do you LOVE bacon?");
    cb2 = new JCheckBox("Do you LOVE cheese?");

    p2.add(cb);
    p2.add(cb2);

    label = new JLabel("This is a label");
    JTextArea tb = new JTextArea("This is a text area");
    textField = new JTextField("text field");

    c.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub
            String s2 = textField.getText();
            label.setText(s2);
        }
    });

    GridBagConstraints gbc = new GridBagConstraints();
    gbc.insets = new Insets(15, 15, 15, 15);

    gbc.gridx = 0;
    gbc.gridy = 0;
    p3.add(label, gbc);
    gbc.gridx = 0;
    gbc.gridy = 1;
    p3.add(tb, gbc);
    gbc.gridx = 0;
    gbc.gridy = 2;
    p3.add(textField, gbc);

    add(p, BorderLayout.SOUTH);
    add(p2, BorderLayout.NORTH);
    add(p3, BorderLayout.CENTER);
    add(p4, BorderLayout.WEST);

    b.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub
            s = "Good job kid, you harvested your corn! \n";

            if (cb.isSelected()) {
                s += " And of course you love bacon! \n";
            }
            if (cb2.isSelected()) {
                s += " Most naturally you love cheese! \n";
            }
            JOptionPane.showMessageDialog(null, s);
        }
    });

}

@Override
public void actionPerformed(ActionEvent e) {
    tb.setText(e.getActionCommand());

}

}

Answer 1

JTextArea tb = new JTextArea("This is a text area");

您正在shadowing您的变量。您将“tb”变量定义为实例变量和局部变量。您不需要局部变量，因为您的actionPerformed()方法无法引用局部变量。

因此，代码应为:

//JTextArea tb = new JTextArea("This is a text area");
tb = new JTextArea("This is a text area");

I'm watching a youtube tutorial series by mybringback

我从来没有弄清楚为什么人们会使用youtube作为教程。

我将从Swing tutorial开始。这样，您不仅可以按照自己的进度阅读教程，而且可以实际下载代码，并编译，测试和更改代码。因此，您从工作代码开始，然后自定义代码以执行所需的操作。