Java Applet：彩绘球不会出现在硬编码位置。 Applet 不保持恒定的大小

Question

我正在制作一个由在屏幕上移动的球组成的小程序。 我将球的初始 X 和 Y 坐标设置为 0，但椭圆形是在距这些点一定距离处绘制的（参见图片）。 另一个问题是，有时当我运行应用程序时，我会得到一个具有所需宽度和高度的小程序，但有时它会较小。我不知道为什么会发生这种情况。

我粘贴了下面的代码：

import java.applet.Applet;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.Timer;


public class StartingPoint extends Applet implements ActionListener
{
    final int DELAY             = 10;
    final int APPLET_WIDTH      = 400; 
    final int APPLET_HEIGHT     = 300;

    int x=0;
    int y=0;
    int ballRadius  = 20;
    int movementX   = 10;
    int movementY   = 10;

    private Image appletImage;
    private Graphics appletGraphics;

    public void init()
    {
        super.init();
        //StartingPoint.this.setSize( APPLET_WIDTH, APPLET_HEIGHT );
    }


    public void start() 
    {
        Timer animationTimer = new Timer(60, this);
        animationTimer.start();
    }

    public void stop()
    {
        super.stop();
    }

    public void destroy()
    {
        super.destroy();
    }


    public void update(Graphics g)
    {
        if(appletImage == null)
        {
            appletImage = createImage( this.getSize().width, this.getSize().height );
            appletGraphics = appletImage.getGraphics();
        }

        //draw applet background
        appletGraphics.setColor(getBackground());
        appletGraphics.fillRect(0, 0, this.getSize().width, this.getSize().height);

        //draw applet foreground
        appletGraphics.setColor(getForeground());
        this.paint( appletGraphics );

        //draw images on the applet
        g.drawImage(appletImage, 0, 0, this);
    }

    public void paint(Graphics g)
    {
        super.paint(g);
        this.setBackground(Color.BLUE);
        g.setColor(Color.RED);
        g.fillOval(this.x, this.y, ballRadius, ballRadius);
    }


    @Override
    public void actionPerformed(ActionEvent e)
    {
        if( (x+movementX) > (this.getWidth()-ballRadius))
        {
            this.x = this.getWidth()-ballRadius;
            this.movementX = -movementX;
        }else if( x+movementX < ballRadius)
        {
            this.x = ballRadius;
            this.movementX = -movementX;
        }
        else
            this.x += movementX;

        if( (y+movementY) > this.getHeight()-ballRadius)
        {
            this.y = this.getHeight()-ballRadius;
            this.movementY = -movementY;
        }else if( y+movementY < ballRadius)
        {
            this.y = ballRadius;
            this.movementY = -movementY;
        }
        else
            this.y += movementY;


        this.repaint();
    }
}

Answer 1

我发现我错在哪里了，这确实有点愚蠢。

actionPerformed() 方法中的这些代码行偏移了 x 和 y 位置：

else
            this.x += movementX;

//....
else
            this.y += movementY;