我有一个 KeyListener 的内部类，它返回一个错误，说“不是抽象的，不会覆盖抽象方法”

Question

我有一个 JPanel，其中包含大约 10 个 JTextField，我希望能够在键盘上单击向上或向下箭头后将焦点设置在特定的文本字段上。因此，如果中间的文本字段被聚焦并单击向上箭头，则焦点将转到其上方的文本字段，同样，如果单击向下箭头，它将聚焦在其下方的文本字段上。我创建了一个 Key Listener 的内部类，其模式类似于我的 ActionListener 类，我认为我可以做到。当我编译它时似乎有一个错误

panelEncodeMain.HandleKeyListener is not abstract and does not override abstract method keyReleased(KeyEvent) in KeyListener。

谁能帮我解决问题？提前致谢。

public panelEncodemain()
{
    //setBackground(Color.WHITE);
    setLayout(new GridBagLayout());
    GridBagConstraints c = new GridBagConstraints();

    HandleControlButton control = new HandleControlButton();
    HandleKeyListener keycontrol = new HandleKeyListener();

    btn_testing = new JButton("Test Focus");
    btn_testing.addActionListener(control);

    lbl_page = new JLabel("Page :");
    lbl_line = new JLabel("Line :");
    lbl_refpage = new JLabel("Ref. Page :");
    lbl_refline = new JLabel("Ref. Line :");
    lbl_transdate = new JLabel("Transaction Date :");
    lbl_desc = new JLabel("Description :");
    lbl_accountcode = new JLabel("Account Code :");
    lbl_codetype = new JLabel("Code Type :");
    lbl_issuedate = new JLabel("Issue Date :");
    lbl_amount = new JLabel("Amount :");

    lbl_page.setFont(new Font("Arial", Font.PLAIN, 20));
    lbl_line.setFont(new Font("Arial", Font.PLAIN, 20));
    lbl_refpage.setFont(new Font("Arial", Font.PLAIN, 20));
    lbl_refline.setFont(new Font("Arial", Font.PLAIN, 20));
    lbl_transdate.setFont(new Font("Arial", Font.PLAIN, 20));
    lbl_desc.setFont(new Font("Arial", Font.PLAIN, 20));
    lbl_accountcode.setFont(new Font("Arial", Font.PLAIN, 20));
    lbl_codetype.setFont(new Font("Arial", Font.PLAIN, 20));
    lbl_issuedate.setFont(new Font("Arial", Font.PLAIN, 20));
    lbl_amount.setFont(new Font("Arial", Font.PLAIN, 20));

    text_page = new JTextField(7);
    text_line = new JTextField(5);
    text_refpage = new JTextField(40);
    text_refline = new JTextField(40);
    text_transdate = new JTextField(10);
    text_desc = new JTextField(40);
    text_desc.addKeyListener(keycontrol);
    text_accountcode = new JTextField(5);
    text_codetype = new JTextField(5);
    text_issuedate = new JTextField(10);
    text_amount = new JTextField(20);


    text_page.setFont(new Font("Arial", Font.PLAIN, 20));
    text_line.setFont(new Font("Arial", Font.PLAIN, 20));
    text_refpage.setFont(new Font("Arial", Font.PLAIN, 20));
    text_refline.setFont(new Font("Arial", Font.PLAIN, 20));
    text_transdate.setFont(new Font("Arial", Font.PLAIN, 20));
    text_desc.setFont(new Font("Arial", Font.PLAIN, 20));
    text_accountcode.setFont(new Font("Arial", Font.PLAIN, 20));
    text_codetype.setFont(new Font("Arial", Font.PLAIN, 20));
    text_issuedate.setFont(new Font("Arial", Font.PLAIN, 20));
    text_amount.setFont(new Font("Arial", Font.PLAIN, 20));


    //text_desc.setEditable(false);

    //first row

    c.gridx = 0;
    c.gridy = 0;
    c.insets = new Insets(5,0,0,10);
    c.anchor = GridBagConstraints.LINE_END;
    add(lbl_page, c);

    c.gridx = 1;
    c.anchor = GridBagConstraints.LINE_START;
    add(text_page, c);

    //second row

    c.gridy++;

    c.anchor = GridBagConstraints.LINE_END;
    c.gridx=0;
    add(lbl_line, c);

    c.gridx = 1;
    c.anchor = GridBagConstraints.LINE_START;
    add(text_line, c);

    //third row

    c.gridy++;

    c.anchor = GridBagConstraints.LINE_END;
    c.gridx=0;
    add(lbl_refpage, c);

    c.gridx = 1;
    c.anchor = GridBagConstraints.LINE_START;
    add(text_refpage, c);

    //fourth row

    c.gridy++;

    c.anchor = GridBagConstraints.LINE_END;
    c.gridx=0;
    add(lbl_refline, c);

    c.gridx = 1;
    c.anchor = GridBagConstraints.LINE_START;
    add(text_refline, c);

    //fifth row

    c.gridy++;

    c.anchor = GridBagConstraints.LINE_END;
    c.gridx=0;
    add(lbl_transdate, c);

    c.gridx = 1;
    c.anchor = GridBagConstraints.LINE_START;
    add(text_transdate, c);

    //sixth row

    c.gridy++;

    c.anchor = GridBagConstraints.LINE_END;
    c.gridx=0;
    add(lbl_desc, c);

    c.gridx = 1;
    c.anchor = GridBagConstraints.LINE_START;
    add(text_desc, c);

    //seventh row

    c.gridy++;

    c.anchor = GridBagConstraints.LINE_END;
    c.gridx=0;
    add(lbl_accountcode, c);

    c.gridx = 1;
    c.anchor = GridBagConstraints.LINE_START;
    add(text_accountcode, c);

    //eighth row

    c.gridy++;

    c.anchor = GridBagConstraints.LINE_END;
    c.gridx=0;
    add(lbl_codetype, c);

    c.gridx = 1;
    c.anchor = GridBagConstraints.LINE_START;
    add(text_codetype, c);

    //ninth row

    c.gridy++;

    c.anchor = GridBagConstraints.LINE_END;
    c.gridx=0;
    add(lbl_issuedate, c);

    c.gridx = 1;
    c.anchor = GridBagConstraints.LINE_START;
    add(text_issuedate, c);

    //tenth row

    c.gridy++;

    c.anchor = GridBagConstraints.LINE_END;
    c.gridx=0;
    add(lbl_amount, c);

    c.gridx = 1;
    c.anchor = GridBagConstraints.LINE_START;
    add(text_amount, c);

    //tenth row

    c.gridy++;

    c.gridx = 1;
    c.anchor = GridBagConstraints.LINE_END;
    add(btn_testing, c);

}

class HandleControlButton implements ActionListener
{
    public void actionPerformed (ActionEvent e)
    {
        Object source = e.getSource();

        if(source == btn_testing)
        {
                text_desc.requestFocus();    
        }
    }
}

class HandleKeyListener implements KeyListener
{
    public void keyTyped(KeyEvent x)
    {
        System.out.println(x);
    }
}
}

我希望能够使用键盘上的向上或向下按钮将焦点从一个文本字段转移到下一个文本字段。

Answer 1

就像在 cmets 中提到的那样，错误意味着您必须从接口 KeyListener 实现所有方法。它有三种方法

• keyTyped（您已经实现）
• keyPressed（未实现）
• KeyReleased（未实现）

所以您可以为这些方法添加一个空实现，但在这种情况下，最简单的方法是扩展类 KeyAdapter 而不是实现 KeyListener（因为 KeyAdapter 实现 KeyListener 并且只实现了空方法，这正是您所需要的在这里）

所以你可以把 KeyListener 类改成这样：

class HandleKeyListener extends KeyAdapter {
    public void keyTyped(KeyEvent x) {
        System.out.println(x);
    }
}

那么它应该可以工作了。