Java-在extern函数中更改JLabel Frontcolor

作为Java初学者，我尝试在windowsbuilder（eclipse插件）的帮助下创建一个窗口应用程序“游戏”。 现在，当我尝试更改extern函数（allblack（））中的标签时，当我按下特定按钮（窗口正确显示）时，控制台会显示以下错误：

如果有人能把它解释成“allblack（）”中的代码和“Inalizalize（）”中的代码一样，我将不胜感激。 谢谢

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看起来变量l1和l2只存在于initialize方法中。 试试这个：

public void allblack() {
    l1.setForeground(Color.black);
    l2.setForeground(Color.black);
}

private JLabel l1,l2;
public void initialize() {

    frmDasLeiterspiel = new JFrame();
    frmDasLeiterspiel.setResizable(false);
    frmDasLeiterspiel.setTitle("Das Leiterspiel");
    frmDasLeiterspiel.setBounds(100, 100, 420, 420);
    frmDasLeiterspiel.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frmDasLeiterspiel.getContentPane().setLayout(null);

    l1 = new JLabel("1");
    l1.setBackground(Color.LIGHT_GRAY);
    l1.setBounds(340, 190, 50, 50);
    l1.setHorizontalAlignment(SwingConstants.CENTER);
    frmDasLeiterspiel.getContentPane().add(l1, BorderLayout.CENTER);

    l2 = new JLabel("2");
    l2.setBackground(Color.LIGHT_GRAY);
    l2.setHorizontalAlignment(SwingConstants.CENTER);
    l2.setBounds(278, 190, 50, 50);
    frmDasLeiterspiel.getContentPane().add(l2);
    [....]
    JButton btnNewButton = new JButton("Roll the dice!");
    btnNewButton.addMouseListener(new MouseAdapter() {
        @Override
        public void mouseClicked(MouseEvent arg0) {
            allblack();
        }
    });
    btnNewButton.setBounds(12, 294, 378, 25);
    frmDasLeiterspiel.getContentPane().add(btnNewButton);
    [...]
    }

---

您正在创建的标签是

initialize

方法的本地标签。替换

JLabel l1=新的JLabel（“1”）带有
l1=新的JLabel（“1”）和
JLabel l2=新的JLabel（“2”）带有
l2=新的JLabel（“2”）以初始化实际标签。
[Pre-sampled import]
public void allblack()
 {
    l1.setForeground(Color.black);
    l2.setForeground(Color.black);
 }
 public void initialize() {

    frmDasLeiterspiel = new JFrame();
    frmDasLeiterspiel.setResizable(false);
    frmDasLeiterspiel.setTitle("Das Leiterspiel");
    frmDasLeiterspiel.setBounds(100, 100, 420, 420);
    frmDasLeiterspiel.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frmDasLeiterspiel.getContentPane().setLayout(null);

    JLabel l1 = new JLabel("1");
    l1.setBackground(Color.LIGHT_GRAY);
    l1.setBounds(340, 190, 50, 50);
    l1.setHorizontalAlignment(SwingConstants.CENTER);
    frmDasLeiterspiel.getContentPane().add(l1, BorderLayout.CENTER);

    JLabel l2 = new JLabel("2");
    l2.setBackground(Color.LIGHT_GRAY);
    l2.setHorizontalAlignment(SwingConstants.CENTER);
    l2.setBounds(278, 190, 50, 50);
    frmDasLeiterspiel.getContentPane().add(l2);
    [....]
    JButton btnNewButton = new JButton("Roll the dice!");
    btnNewButton.addMouseListener(new MouseAdapter() {
        @Override
        public void mouseClicked(MouseEvent arg0) {
            allblack();
        }
    });
    btnNewButton.setBounds(12, 294, 378, 25);
    frmDasLeiterspiel.getContentPane().add(btnNewButton);
    [...]
    }

public void allblack() {
    l1.setForeground(Color.black);
    l2.setForeground(Color.black);
}

private JLabel l1,l2;
public void initialize() {

    frmDasLeiterspiel = new JFrame();
    frmDasLeiterspiel.setResizable(false);
    frmDasLeiterspiel.setTitle("Das Leiterspiel");
    frmDasLeiterspiel.setBounds(100, 100, 420, 420);
    frmDasLeiterspiel.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frmDasLeiterspiel.getContentPane().setLayout(null);

    l1 = new JLabel("1");
    l1.setBackground(Color.LIGHT_GRAY);
    l1.setBounds(340, 190, 50, 50);
    l1.setHorizontalAlignment(SwingConstants.CENTER);
    frmDasLeiterspiel.getContentPane().add(l1, BorderLayout.CENTER);

    l2 = new JLabel("2");
    l2.setBackground(Color.LIGHT_GRAY);
    l2.setHorizontalAlignment(SwingConstants.CENTER);
    l2.setBounds(278, 190, 50, 50);
    frmDasLeiterspiel.getContentPane().add(l2);
    [....]
    JButton btnNewButton = new JButton("Roll the dice!");
    btnNewButton.addMouseListener(new MouseAdapter() {
        @Override
        public void mouseClicked(MouseEvent arg0) {
            allblack();
        }
    });
    btnNewButton.setBounds(12, 294, 378, 25);
    frmDasLeiterspiel.getContentPane().add(btnNewButton);
    [...]
    }