Java 图形绘制不正确 [英] Java graphic not painting properly

问题描述

我写了以下代码

   import java.awt.BorderLayout;
import java.awt.Graphics;

import javax.swing.JFrame;
import javax.swing.JPanel;

final public class Test
{

    JFrame frame;
    DrawPanel drawPanel;
    boolean up = false;
    boolean down = true;
    boolean left = false;
    boolean right = true;
    private int timeStep = 0;
    private int ballYTravel = 100;
    private int BALL_NUM = 24;

    public static void main(String... args)
    {
        new Test().go();
    }

    private void go()
    {
        frame = new JFrame("Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        drawPanel = new DrawPanel();

        frame.getContentPane().add(BorderLayout.CENTER, drawPanel);

        frame.setResizable(false);
        frame.setSize(800, 600);
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
        moveIt();
    }

    class DrawPanel extends JPanel
    {
        private static final long serialVersionUID = 1L;
        public double getY(int i, int t) {
            return 200 + ballYTravel / 2 * (Math.sin(timeStep * (i / 200 + 0.08)));
        }

        public void paintComponent(Graphics g)
        {    
            for (int k = 0; k < BALL_NUM; k++ ) {
                g.fillRect(100  + 20 *k , (int) getY(k, timeStep), 6, 6);
            }
            timeStep++;

        }
    }



    private void moveIt()
    {
        while (true)
        {

            try
            {
                Thread.sleep(10);
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
            frame.repaint();
        }
    }
    }

它运行和动画，但是它的动画方式与我引用它的 Javascript 代码不同，可以在此处找到 http://codepen.io/anon/pen/ZYQoQZ

It runs and animates, however it is not animating in the same fashion as the Javascript code I referenced it from which can be found here http://codepen.io/anon/pen/ZYQoQZ

任何有助于理解原因的帮助

any help in understanding why is appreciated

推荐答案

有(可能)两个基本问题...

There are (possibly) two basic problems...

1. 在 getY 中，您忽略了参数 t 并使用 timeStep 代替，而从技术上讲，这可能不会巨大的差异，这是一个值得关注的领域
2. 您遇到了整数除法问题.i/200 将导致 int 结果，您真正想要的是 double.将其更改为 i/200d

1. In getY, you are ignoring the parameter t and using timeStep instead, while, technically, this probably isn't going to make a MASSIVE difference, it is an area of concern
2. You have an integer division issue. i/200 will result in int result, where you really want a double. Change it to i/200d

例如...

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

final public class Test {

    private int timeStep = 0;
    private final int ballYTravel = 100;
    private final int BALL_NUM = 24;

    public static void main(String... args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new DrawPanel());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    class DrawPanel extends JPanel {

        private static final long serialVersionUID = 1L;

        public DrawPanel() {
            new Timer(10, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    timeStep++;
                    repaint();
                }
            }).start();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 200);
        }

        public double getY(int i, int t) {
            return 100 + ballYTravel / 2 * (Math.sin(t * (i / 200d + 0.08)));
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            for (int k = 0; k < BALL_NUM; k++) {
                g.fillRect(10 + 20 * k, (int) getY(k, timeStep), 6, 6);
            }

        }
    }
}

您还破坏了绘制链，从长远来看这会导致您出现问题，请确保您正在调用 super.paintComponent...

You're also breaking the paint chain, which is going to cause you issues in the long run, make sure you are calling super.paintComponent...

欲了解更多详情，请参阅...

For more details see...

• 执行自定义绘画
• 在 AWT 和 Swing 中绘画
• Swing 中的并发
• 如何使用 Swing 计时器
• 初始线程

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