Question

我正在做一个小程序，其中一些球在盒子里弹跳。这个逻辑已经在一个名为Ball.java的类中完成，并且球正在弹跳并正常移动。

我想更进一步，在Jframe内部绘制一个矩形，当内部有两个球时，让球表现出特定的方式。只有2个球在矩形的边界内移动。进入矩形的其他球应该冻结到2中的一个目前移动的球离开它。除非存在，否则离开矩形的移动球应该冻结框中的另一个球意味着矩形永远不应该是空的。

下面是我应该实现的逻辑，我在paincomponents（）方法中用g.drawRect(75, 75, 200, 200);绘制了矩形，我无法让球知道它们在那个矩形内。

package bouncingball;

import bouncingball.Ball;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import javax.swing.JPanel;

public class BallPanel extends JPanel {

private Ball ball;
private ArrayList<Ball> balls = new ArrayList();
private int ballsInside = 0;

public BallPanel() {
    addMouseListener(new Mouse());
}

//method for creating a new ball
private void newBall(MouseEvent click) {
    ball = new Ball(this);
    balls.add(ball);
    Thread t = new Thread(ball);
    t.setPriority(Thread.NORM_PRIORITY);
    t.start();
    System.out.println("New ball created");
}

public void animate() {
    while (true) {
        repaint();
}

/* public synchronized void countIn() throws InterruptedException {
 while (ballsInside < 2){
 wait();
 }
 ballsInside++;
 notifyAll();

 }

 public synchronized void countMaxIn() throws InterruptedException {
 while (ballsInside == 2){
 wait();
 }
 ballsInside--;
 notifyAll();

 }*/
private class Mouse extends MouseAdapter {

    @Override
    public void mousePressed(final MouseEvent event) {
        newBall(event);
    }
}

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawRect(75, 75, 200, 200);
    for (Ball ball : balls) {
        if (ball != null) {
            ball.draw(g);
        }
    }
}
}

和我的球类

package bouncingball;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.util.Random; 
import java.lang.Runnable;
import javax.swing.JPanel;
import java.util.ArrayList;

public class Ball implements Runnable {

public final static Random random = new Random();

final static int SIZE = 30;
final static int MAX_SPEED = 5;

BallPanel panel = new BallPanel();

private int x;
private int y;

private int dx;
private int dy;

private Color color = Color.BLUE;
//private ArrayList<Ball> balls ;


@Override   
public void run() {
    while (true) {
        move();
        try {
            Thread.sleep(40);  // wake up roughly 25 frames per second
        } catch (InterruptedException exception) {
            exception.printStackTrace();
        }
    }
}

public Ball(BallPanel panel) {
    this.panel = panel;
    x = random.nextInt(panel.getWidth());
    y = random.nextInt(panel.getHeight());
    dx = random.nextInt(2 * MAX_SPEED) - MAX_SPEED;
    dy = random.nextInt(2 * MAX_SPEED) - MAX_SPEED;
}

public void draw(Graphics g) {
    g.setColor(color);
    g.fillOval(x, y, SIZE, SIZE);
}

public void move() {

    // check for bounce and make the ball bounce if necessary
    //
    if (x < 0 && dx < 0) {
        //bounce off the left wall 
        x = 0;
        dx = -dx;
    }
    if (y < 0 && dy < 0) {
        //bounce off the top wall
        y = 0;
        dy = -dy;
    }
    if (x > panel.getWidth() - SIZE && dx > 0) {
        //bounce off the right wall
        x = panel.getWidth() - SIZE;
        dx = -dx;
    }
    if (y > panel.getHeight() - SIZE && dy > 0) {
        //bounce off the bottom wall
        y = panel.getHeight() - SIZE;
        dy = -dy;
    }

    //make the ball move
    x += dx;
    y += dy;
}
}

Answer 1

使用一个整数semaphore，允许2个球进入直到其他球阻挡。

private final Semaphore entryTickets = new Semaphore(2, true);

在球中：

entryTickets.acquire(); // Enter
...
entryTickets.release(); // Leave

我希望球能够知道它们位于JPanel的矩形内

1 个答案: