Java语言。全局JLabels

Question

下面是我在底部的代码。首先要做的是。这不是家庭作业。这是我下一次考试的学习指南。我在将JLabel公开以便在keyboardlistener方法中使用它时遇到了问题。你能不能也看一下，看看当我把JLabel公之于众的时候，它看起来是否合适？

public class Driver {
    public static void main( String[] args ) {
        Driver gui = new Driver();
        // No other Java code should be added to this method
    }

    /**
     * Our driver class
     */
    public Driver() {
        Window win = new Window();
        win.setLocation(50, 30);
        win.setSize(500, 400);
        win.setBackground( Color.DARK_GRAY );

        Oval circle;
        circle = new Oval(win.getWidth()/2,win.getHeight()/2,200,200);
        circle.setBackground( Color.MAGENTA );
        circle.setLocation(150,100);
        win.add(circle);

        Triangle t;
         t = new Triangle(win.getWidth()/2,win.getHeight()/2,120, 120, 0);
         t.setSize(30,40);
         t.setBackground( Color.MAGENTA );
         t.setLocation(295,110);
         win.add( t );


         Triangle tt;
         tt = new Triangle(win.getWidth()/100, win.getHeight()/2, 120, 120, 0);
         tt.setSize(30,40);
         tt.setBackground( Color.MAGENTA );
         tt.setLocation(175,110);
         win.add( tt );

         Oval eye;
         eye = new Oval(win.getWidth()/2,win.getHeight()/2,200,200);
         eye.setBackground( Color.BLUE );
         eye.setSize(25,25);
         eye.setLocation(275,160);
         win.add(eye);

        Oval eye2;
        eye2 = new Oval(win.getWidth()/2,win.getHeight()/2,200,200);
        eye2.setSize(25,25);
        eye2.setBackground( Color.BLUE );
        eye2.setLocation(210,160);
        win.add(eye2);

        Oval pupil1;
        pupil1 = new Oval(win.getWidth()/2,win.getHeight()/2,200,200);
        pupil1.setSize(10,10);
        pupil1.setBackground( Color.BLACK );
        pupil1.setLocation(215,170);
        win.add(pupil1);

        Oval pupil2;
        pupil2 = new Oval(win.getWidth()/2,win.getHeight()/2,200,200);
        pupil2.setSize(10,10);
        pupil2.setBackground( Color.BLACK );
        pupil2.setLocation(280,170);
        win.add(pupil2);

        Color myColor = new Color (12,15,23);
        Triangle nose;
        nose = new Triangle(win.getWidth()/100, win.getHeight()/2, 120, 120, 0);
        nose.setSize(30,40);
        nose.setBackground( myColor );
        nose.setLocation(240,190);
        win.add( nose );

        Rectangle mouth = new Rectangle (win.getWidth()/2,win.getHeight()/2,200,200);
        mouth.setSize(50,20);
        mouth.setBackground(Color.BLACK);
        mouth.setLocation(230,250);
        win.add(mouth);

        Line whisker1;
        whisker1 = new Line(280,245,255,240);
        whisker1.setBackground( Color.BLACK );
        win.add( whisker1 );

        Line whisker2;
        whisker2 = new Line(280,220,255,240);
        whisker2.setBackground( Color.BLACK );
        win.add( whisker2 );

        Line whisker3;
        whisker3 = new Line(220,245,255,240);
        whisker3.setBackground( Color.BLACK );
        win.add( whisker3 );

        Line whisker4;
        whisker4 = new Line(220,220,255,240);
        whisker4.setBackground( Color.BLACK );
        win.add( whisker4 );

        final JLabel catName;
        catName = new JLabel();
        catName.setText("George, he likes buses :(");
        catName.setBounds(200, 300, 150, 20);
        catName.setForeground(Color.WHITE);
        win.add(catName);


        Line mouth2nose;
        mouth2nose = new Line(255,220,255,250);
        mouth2nose.setBackground( Color.BLACK );
        win.add( mouth2nose );
        // Attach the keyboard listener
        KeyboardListener kl = new KeyboardListener(this, win);

        // Once all components are added, set visibility to make the window show up
        win.setVisible(true);
    }

    /**
     * Event handler for KeyboardListener.
     * Handle a keyboard press event (when focused on the window)
     * 
     * @param key The key that was pressed as the code from KeyEvent.
     */
    public void handleKeyboardEvent(int key) {
        if (key == KeyEvent.VK_UP) {
            System.out.println("DEBUG: Key = UP");
            Driver.catName(+0,+1,+0,+0);
        } else if (key == KeyEvent.VK_DOWN) {
            System.out.println("DEBUG: Key = DOWN");
            Driver.catName(+0,-1,+0,+0);
        } else if (key == KeyEvent.VK_LEFT) {
            System.out.println("DEBUG: Key = LEFT");
            Driver.catName(-1,+0,+0,+0);
        } else if (key == KeyEvent.VK_RIGHT) {
            System.out.println("DEBUG: Key = RIGHT");
            Driver.catName(+1,+0,+0,+0);
        }
    }

}

Answer 1

我建议您将JLabel catName定义为类成员并在构造函数中进行初始化，之后您将能够在该类的任何方法中使用它。

示例：

public class Driver {

    private  JLabel catName;
    public static void main( String[] args ) {
        Driver gui = new Driver();
        // No other Java code should be added to this method
    }

// the constructor
public Driver() {
    Window win = new Window();
    win.setLocation(50, 30);
    ....
    ....
    catName = new JLabel();
    catName.setText("George, he likes buses :(");
    catName.setBounds(200, 300, 150, 20);
    catName.setForeground(Color.WHITE);
    win.add(catName);
    ....