Question

我创建了一个简单的GUI，可以在屏幕上移动3个PNG，但它无法正常工作。

以下是我拥有的代码我是GUI和swing的新手，因此可能会出现一些非常简单的常见错误，我为此向您道歉：

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
 public class MovingPictures extends JPanel implements ActionListener
 {
private Timer timer;
Stars star;
public MovingPictures()
{
    setPreferredSize(new Dimension(800,800));

    timer = new Timer(1,this);
    timer.addActionListener(this);
    timer.start();
}

public void paintComponent(Graphics g)
{
    super.paintComponent(g);
    g.drawImage(star.getStar(),star.getStarX(),star.getStarY(),null);
    g.drawImage(star.getStar2(),star.getStar2X(),star.getStar2Y(),null);
    g.drawImage(star.getStar3(),star.getStar3X(),star.getStar3Y(),null);
}

public void actionPerformed(ActionEvent e)
{
    star.up();
    star.across();
    star.diagonal();
    repaint();
}

public class Stars
    {
    private Image stars;
    private Image stars2;
    private Image stars3;
    private int starX;
    private int starY;
    private int star2X;
    private int star2Y;
    private int star3X;
    private int star3Y;
    public Stars()
        {
        stars = new ImageIcon("star.png").getImage();
        stars2 = new ImageIcon("star2.png").getImage();
        stars3 = new ImageIcon("star3.png").getImage();
        starX = 0;
        starY = 50;
        star2X = 100;
        star2Y = 0;
        star3X = 0;
        star3Y = 0;
    }

    public void up()
    {
        if(starY == 790)
            starY = 0;
        else
            starY += 2;

    }

    public void across()
    {
        if(star2X == 790)
            star2X = 0;
        else
            star2X +=2;
    }

    public void diagonal()
    {
        if (star3X == 790 )
        {
            star3X=0;
            star3Y =0;
        }
        else
        {
            star3X += 2;
            star3Y += 2;
        }
    }

    public int getStarX()
    {
        return starX;
    }

    public int getStarY()
    {
        return starY;
    }

    public int getStar2X()
    {
        return star2X;
    }

    public int getStar2Y()
    {
        return star2Y;
    }

    public int getStar3X()
    {
        return star3X;
    }

    public int getStar3Y()
    {
        return star3Y;
    }

    public Image getStar()
    {
        return stars;
    }

    public Image getStar2()
    {
        return stars2;
    }

    public Image getStar3()
    {
        return stars3;
    }

}
public static void main(String[] args)
{
    JFrame frame = new JFrame();
    frame.setTitle(" Star Field ");
    frame.setSize(new Dimension(800,800));
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    MovingPictures panel = new MovingPictures();
    frame.add(panel);
    panel.setBackground(Color.BLACK);
    frame.setVisible(true);


}
}

我已编译并运行此程序，如果您有任何帮助，我们将不胜感激。

Answer 1

请注意更改：

Stars star;

要：

Stars star = new Stars();

防止NullPointerException在star被实例化/创建之前被引用。{/ p>

简单的GUI，可以在屏幕上移动3个PNG - 无法正常工作

1 个答案: