如何将值从一个 JLabel 传输到另一个 JLabel？

我有这个计算器，但我不知道如何获取其中的值resultpane单击“完成”按钮时到第一个文本框。

我是 Java 新手。我已经尝试这样做，但我一直收到错误。

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.NumberFormat;
import javax.swing.AbstractAction;
import static javax.swing.Action.NAME;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestCalculator {

public static void main(String[] args) {
    new TestCalculator();
}

public TestCalculator() {
    EventQueue.invokeLater(new Runnable() {
        @Override
        public void run() {
            try {
                UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
            } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
            }

            ResultPane resultPane = new ResultPane();

            JFrame frame = new JFrame("Testing");
            frame.setGlassPane(resultPane);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setLayout(new BorderLayout());
            frame.add(new CalculatorPane(resultPane));
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        }
    });
}

public class ResultPane extends JPanel {

    private JLabel result;
    private Timer timer;

    private int xDelta = (Math.random() > 0.5) ? 1 : -1;
    private int yDelta = (Math.random() > 0.5) ? 1 : -1;

    ;

    public ResultPane() {
        setOpaque(false);
        setLayout(null);
        result = new JLabel();
        Font font = result.getFont();
        font = font.deriveFont(Font.BOLD, 26f);
        result.setFont(font);
        add(result);
        timer = new Timer(40, new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                Point point = result.getLocation();
                point.x += xDelta;
                point.y += yDelta;
                if (point.x < 0) {
                    point.x = 0;
                    xDelta *= -1;
                } else if (point.x + result.getWidth() > getWidth()) {
                    point.x = getWidth() - result.getWidth();
                    xDelta *= -1;
                }
                if (point.y < 0) {
                    point.y = 0;
                    yDelta *= -1;
                } else if (point.y + result.getHeight() > getHeight()) {
                    point.y = getHeight() - result.getHeight();
                    yDelta *= -1;
                }
                result.setLocation(point);
                repaint();
            }

        });
        timer.start();
    }

    public void setResult(Number number) {
        result.setText("Result: " + NumberFormat.getNumberInstance().format(number));
        result.setSize(result.getPreferredSize());
        setVisible(true);
    }

}

public class CalculatorPane extends JPanel {

    private final ResultPane resultPane;

    private final JLabel firstNumberLabel = new JLabel("First Number:");
    private final JLabel secondNumberLabel = new JLabel("Second Number:");

    private final JTextField firstNumberField = new JTextField(5);
    private final JTextField secondNumberField = new JTextField(5);

    public CalculatorPane(ResultPane resultPane) {

        setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridwidth = GridBagConstraints.REMAINDER;

        this.resultPane = resultPane;

        JPanel fields = new JPanel();
        fields.add(firstNumberLabel);
        fields.add(firstNumberField);
        fields.add(secondNumberLabel);
        fields.add(secondNumberField);

        add(fields, gbc);

        JPanel buttons = new JPanel();
        buttons.add(new JButton(new AddAction()));
        buttons.add(new JButton(new SubtractAction()));
        buttons.add(new JButton(new MultiplyAction()));
        buttons.add(new JButton(new DivideAction()));
        buttons.add(new JButton(new ToText1Action()));

        add(buttons, gbc);

    }

    public class AddAction extends AbstractAction {

        public AddAction() {
            putValue(NAME, "+");
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            try {
                double num1 = Double.parseDouble(firstNumberField.getText());
                double num2 = Double.parseDouble(secondNumberField.getText());

                double result = num1 + num2;

                //num1.setResult(firstNumberField);
                resultPane.setResult(result);
            } catch (NumberFormatException exp) {
            }
        }

    }
    public class SubtractAction extends AbstractAction {

        public SubtractAction() {
            putValue(NAME, "-");
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            try {
                double num1 = Double.parseDouble(firstNumberField.getText());
                double num2 = Double.parseDouble(secondNumberField.getText());

                double result = num1 - num2;
                resultPane.setResult(result);
            } catch (NumberFormatException exp) {
            }
        }

    }
    public class MultiplyAction extends AbstractAction {

        public MultiplyAction() {
            putValue(NAME, "x");
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            try {
                double num1 = Double.parseDouble(firstNumberField.getText());
                double num2 = Double.parseDouble(secondNumberField.getText());

                double result = num1 * num2;
                resultPane.setResult(result);
            } catch (NumberFormatException exp) {
            }
        }

    }
    public class DivideAction extends AbstractAction {

        public DivideAction() {
            putValue(NAME, "/");
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            try {
                double num1 = Double.parseDouble(firstNumberField.getText());
                double num2 = Double.parseDouble(secondNumberField.getText());

                double result = num1 / num2;
                resultPane.setResult(result);
            } catch (NumberFormatException exp) {
            }
        }

    }
    public class ToText1Action extends AbstractAction {
        public ToText1Action() {
            putValue(NAME, "Finish");
        }
        @Override
        public void actionPerformed(ActionEvent e) {
            try {

                //i would like to put it here


            } catch (NumberFormatException exp) {
            }
        }
    }
}
}

为您的 ResultPane 提供一个新的公共方法，允许您从其 JLabel 中提取文本，如下所示：

  public String getResultText() {
     return result.getText();
  }

然后当您想要获取该字段的文本时调用它：

  public class ToText1Action extends AbstractAction {
     public ToText1Action() {
        putValue(NAME, "Finish");
     }

     @Override
     public void actionPerformed(ActionEvent e) {
         String resultText = resultPane.getResultText();
         double number = // extract number from resultText
         firstNumberField.setText(number);
     }
  }

更好的是，只需将最新结果值存储在作为类的实例字段的双变量中，例如称为lastResult并用它设置第一个数字字段。

请注意，不应有空的 catch 块。

Edit

例如：

public class CalculatorPane extends JPanel {
  private final ResultPane resultPane;
  private final JLabel firstNumberLabel = new JLabel("First Number:");
  private final JLabel secondNumberLabel = new JLabel("Second Number:");
  private final JTextField firstNumberField = new JTextField(5);
  private final JTextField secondNumberField = new JTextField(5);

  private double result = 0.0;   // ****** declared here

  // ***** etc..... *****

  public class DivideAction extends AbstractAction {

     public DivideAction() {
        putValue(NAME, "/");
     }

     @Override
     public void actionPerformed(ActionEvent e) {
        try {
           double num1 = Double.parseDouble(firstNumberField.getText());
           double num2 = Double.parseDouble(secondNumberField.getText());

           result = num1 / num2; // ****** note variable not declared
           resultPane.setResult(result);
        } catch (NumberFormatException exp) {
           // show error message
           // set text fields to "0"
        }
     }

  }

  public class ToText1Action extends AbstractAction {
     public ToText1Action() {
        super("Finish");
        putValue(MNEMONIC_KEY, KeyEvent.VK_F);
     }

     @Override
     public void actionPerformed(ActionEvent e) {
        firstNumberField.setText(String.format("%.2f", result));
     }
  }