JLabel不會在MouseEvent上更改顏色嗎？ 爪哇

Question

我已經在此程序上添加了一段時間，現在可以通過一個簡單的計算器緩慢地開發它，但是現在該程序沒有錯誤，但是沒有提供我想要的輸出。 它應該將顏色更改為藍色，但不會。 我添加了resultPane.setForeground（Color.BLUE）; 但不會更新JLabel

public class TestCalculator {
private ResultPane resultPane;

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

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

            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);
        HandlerClass handler = new HandlerClass();
        result.addMouseListener(handler);
        result.addMouseMotionListener(handler);
        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(NumberFormat.getNumberInstance().format(number));
        result.setSize(result.getPreferredSize());
        setVisible(true);
    }
    public String getResultText() {
        return result.getText();
    }

}

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 double result = 0.0;

    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()));

        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;
                resultPane.setResult(result);
                String resultText = resultPane.getResultText();
            firstNumberField.setText(resultText);
            } 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);
                String resultText = resultPane.getResultText();
            firstNumberField.setText(resultText);
            } 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);
                String resultText = resultPane.getResultText();
            firstNumberField.setText(resultText);
            } 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);
                String resultText = resultPane.getResultText();
                firstNumberField.setText(resultText);
            } catch (NumberFormatException exp) {
            }
        }
    }

}
private class HandlerClass implements MouseListener, MouseMotionListener {
        public void mouseClicked(MouseEvent event) {
        resultPane.setForeground(Color.BLUE);
        }
        public void mouseReleased(MouseEvent event) {
        }
        public void mousePressed(MouseEvent event) {
        }
        public void mouseExited(MouseEvent event) {
        }
        public void mouseEntered(MouseEvent event) {
        }
        public void mouseMoved(MouseEvent event) {
        }
        public void mouseDragged(MouseEvent event){
        }
    }


}

Answer 1

在MouseListener您設置的是JPanel的前景色，而不是JLabel的：

public void mouseClicked(MouseEvent event) {
    resultPane.setForeground(Color.BLUE); // This is the problem
}

resultPane是您的自定義JPanel。 您需要對其進行更改，以設置此自定義面板中包含的JLabel的前景色。 我只ResultPane這樣向ResultPane添加一個方法：

public void setLabelForeground(Color color) {
    result.setForeground(color);
}

然后調用resultPane.setLabelForeground(Color.BLUE); 在MouseListener 。

另外，不確定這是否是您要嘗試的操作，但是當您單擊JLabel時，這仍然只會更改前景色...？