如何控制线程(控制球速)？

Question

我有个问题。我在学java。在这段代码中，我想要减慢/加快我单击“更慢/更快”菜单按钮后创建的球。我的意思是，当我添加了球，当我添加的球在移动，然后我点击了慢或快按钮，正在移动的球具有相同的速度，而我点击按钮后创建的球，球的速度必须改变。

我在BallRunnable类中尝试了锁定和解锁方法，但它不起作用。你能给我一个建议吗？谢谢:)

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import javax.swing.*;
import java.util.List;
import java.util.concurrent.locks.*;

public class BallBounce {
    public static void main(String[] args) {
        JFrame frame = new BounceFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}
/**
    A runnable that animates a bouncing ball.
*/
class BallRunnable implements Runnable {
    public BallRunnable(Ball aBall, JPanel ballPanel) { 
        ball = aBall; this.ballPanel = ballPanel;
        ballLock = new ReentrantLock();
    }
    public void run() {
        ballLock.lock();
        try {
            for (int i = 1; i <= STEPS; i++) {
                ball.move(ballPanel.getBounds()); // update the location of the ball
                ballPanel.paint(ballPanel.getGraphics());
                Thread.sleep((long)(DELAY * change));
            }
        } catch (InterruptedException e) { System.out.println("what"); }
        finally { ballLock.unlock(); }
    }
    public static void print() { System.out.println(DELAY * change); }
    public static void setdoublechange() {
        change = change * 2;
    }
    public static void sethalfchange() {
        change = change / 2;
    }
    private Ball ball;
    private JPanel ballPanel;
    public static final int STEPS = 1000;
    public static final int DELAY = 3;
    private static double change = 1;
    private static Lock ballLock;
}
class BallRunnable2 implements Runnable {
    public BallRunnable2(Ball aBall, JPanel ballPanel) { 
        ball = aBall; this.ballPanel = ballPanel;
    }
    public void run() {
        ballLock.lock();
        try {
            Thread.sleep(100);
            for (int i = 1; i <= STEPS; i++) {
                ball.move(ballPanel.getBounds()); // update the location of the ball
                ballPanel.paint(ballPanel.getGraphics());
                Thread.sleep(DELAY * change);
            }
        } catch (InterruptedException e) { }
        finally { ballLock.unlock(); }
    }
    public static void setdoublechange() {
        change = change * 2;
    }
    public static void sethalfchange() {
        change = change / 2;
    }
    private Ball ball;
    private JPanel ballPanel;
    public static final int STEPS = 1000;
    public static final int DELAY = 3;
    public static int change = 1;
    private Lock ballLock;
}
/**
    A ball that moves and bounces off the edges of a rectangle
*/
class Ball {
    /**
        Moves the ball to the next position, reversing direction if it hits one of the edges
     */
    public void move(Rectangle2D bounds) { // java.awt.geom.Rectangle2D
        x += dx; y += dy;
        if (x < bounds.getMinX()) { x = bounds.getMinX(); dx = -dx; }
        if (x + XSIZE >= bounds.getMaxX()) { x = bounds.getMaxX() - XSIZE; dx= -dx; }
        if (y < bounds.getMinY()) { y = bounds.getMinY(); dy = -dy; }
        if (y + YSIZE >= bounds.getMaxY()) { y = bounds.getMaxY() - YSIZE; dy = -dy; }
    }
    /**
        Gets the shape of the ball at its current position.
     */
    public Ellipse2D getShape() { return new Ellipse2D.Double(x, y, XSIZE, YSIZE); }

    private static final int XSIZE = 15;
    private static final int YSIZE = 15;
    private double x = 0;
    private double y = 0;
    private double dx = 1;
    private double dy = 1;
}
/**
    The panel that draws the balls.
*/
class BallPanel extends JPanel {
    /**
        Add a ball to the panel.
        @param b the ball to add
     */
    public void add(Ball b) {
        balls.add(b);
    }
    
    public void paintComponent (Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        for (Ball b : balls) { g2.fill(b.getShape()); }
    }
    private List<Ball> balls = new ArrayList<>();
}
class BounceFrame extends JFrame {
    public BounceFrame() {
        setTitle("BounceThread");
        setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
        ballPanel = new BallPanel(); add(ballPanel, BorderLayout.CENTER);
        JPanel buttonPanel = new JPanel();
        addButton(buttonPanel, "Add 1", new ActionListener() { 
            public void actionPerformed(ActionEvent event) { addBall1(); }
        });
        addButton(buttonPanel, "Add 2", new ActionListener() { 
            public void actionPerformed(ActionEvent event) { addBall2(); }
        });
        addButton(buttonPanel, "Close", new ActionListener() {
            public void actionPerformed(ActionEvent event) { System.exit(0); }
        });
        // addButton(buttonPanel, "Close", (ActionEvent event) -> System.exit(0));
        add(buttonPanel, BorderLayout.SOUTH);
        
        JMenu speedMenu = new JMenu("Speed");
        JMenuItem fasterItem = speedMenu.add(new fasterAction("Faster"));
        JMenuItem slowerItem = speedMenu.add(new slowerAction("Slower"));
        
        JMenuBar menuBar = new JMenuBar();
        setJMenuBar(menuBar);
        menuBar.add(speedMenu);
    }
    private void addButton(Container container, String title, ActionListener listener) {
        JButton button = new JButton(title);
        container.add(button);
        button.addActionListener(listener);
    }
    /**
        Adds a bouncing ball to the canvas and starts a thread to make it bounce
     */
    public void addBall1() {
        Ball b = new Ball();
        ballPanel.add(b);
        Runnable r = new BallRunnable(b, ballPanel);
        Thread t = new Thread(r);
        t.start();
    }
    public void addBall2() {
        Ball b1 = new Ball();
        Ball b2 = new Ball();
        ballPanel.add(b1);
        ballPanel.add(b2);      
        Runnable r1 = new BallRunnable(b1, ballPanel);
        Runnable r2 = new BallRunnable2(b2, ballPanel);
        Thread t1 = new Thread(r1);
        Thread t2 = new Thread(r2);
        t1.start();
        t2.start();
    }
    
    private BallPanel ballPanel;
    public static final int DEFAULT_WIDTH = 450;
    public static final int DEFAULT_HEIGHT = 350; 
}

class fasterAction extends AbstractAction {
    public fasterAction(String name) { super(name); }
    
    public void actionPerformed(ActionEvent event) {
        BallRunnable.sethalfchange();
        BallRunnable2.sethalfchange();
    }
}
class slowerAction extends AbstractAction {
    public slowerAction(String name) { super(name); }
    
    public void actionPerformed(ActionEvent event) {
        BallRunnable.setdoublechange();
        BallRunnable2.setdoublechange();
    }
}

Answer 1

增加Thread.sleep()值(单位为毫秒)

Answer 2

更改球的dx和/或dy (当满足特定条件时)。

如果我没记错，<dx，dy>是球的速度。