Java Graphics2D 移动物体停在中间

Question

我很难弄清楚为什么这个移动的矩形正好停在 Jpanel 的中间。 Timer 没有停止，似乎中间有一个边界。有人可以为我解释一下吗？我怎样才能让它一路移动（800）？

这是我的代码：

public class TestDemo extends JPanel implements ActionListener {
  private static final long serialVersionUID = 1L;
  private int x;
  private int y;
  Timer timer;

TestDemo() {
    x = 0;
    y = 0;
    this.setBackground(Color.BLACK);
    timer = new Timer(10, this);
    timer.start();
}

public void paint(Graphics g) {
    super.paint(g);
    Graphics2D g2d = (Graphics2D) g;
    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
    g2d.scale(1, 1);
    g2d.setPaint(Color.RED);
    g2d.fill(new Rectangle2D.Double(getX(), getY(), 20, 20));
}

public void actionPerformed(ActionEvent e) {
    setX(getX() + 1);
    repaint();
}

public static void main(String[] args) {
    JFrame frame = new JFrame("Moving star");
    JPanel testDemo = new TestDemo();
    testDemo.setSize(800, 200);
    frame.add(testDemo);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(800, 600);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}

public int getX() {
    return x;
}
public void setX(int x) {
    this.x = x;
}
public int getY() {
    return y;
}
public void setY(int y) {
    this.y = y;
}
}

Answer 1

该代码覆盖了已经存在并用于其他目的的方法。这是主要问题。
对于自定义绘画任何 JComponent，请使用 paintComponent(..) 而不是 paint(..)

这是实现了两项更改的（工作）代码。

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;

public class TestDemo extends JPanel implements ActionListener {

    private static final long serialVersionUID = 1L;
    private int x1;
    private int y1;
    Timer timer;

    TestDemo() {
        x1 = 0;
        y1 = 0;
        this.setBackground(Color.BLACK);
        timer = new Timer(10, this);
        timer.start();
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
        g2d.scale(1, 1);
        g2d.setPaint(Color.RED);
        g2d.fill(new Rectangle2D.Double(getX1(), getY1(), 20, 20));
    }

    public void actionPerformed(ActionEvent e) {
        setX1(getX1() + 1);
        repaint();
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Moving star");
        JPanel testDemo = new TestDemo();
        testDemo.setSize(800, 200);
        frame.add(testDemo);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(800, 600);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public int getX1() {
        return x1;
    }

    public void setX1(int x1) {
        this.x1 = x1;
    }

    public int getY1() {
        return y1;
    }

    public void setY1(int y1) {
        this.y1 = y1;
    }
}

Java Graphics2D 移动物体停在中间

Java Graphics2D moving object stopped in the middle

java

swing

jpanel

graphics2d