Java“简单”撞球/碰撞练习

Question

我通过其他类似的q/a读过，但需要特别的帮助，以便如何让球彼此反弹。

• 该程序具有用户输入的重绘速度和球的数量。
• 我可以让他们反弹离开墙壁就好了。

这里是我的代码：

（进口ArgsProcessor; 进口sedgewick.StdDraw;）

public static void main(String[] args) { 
    ArgsProcessor ap = new ArgsProcessor(args); 
    //request from user - get refresh rate and number of balls 
    int pause = ap.nextInt("Enter pause time:"); 
    int numBalls = ap.nextInt("How many balls will you put into play?"); 

    // set the scale of the coordinate system 

    StdDraw.setXscale(-1.0, 1.0); 
    StdDraw.setYscale(-1.0, 1.0); 

    // initial values 
    int[] balls = new int[numBalls]; 
    double[] positionX = new double[numBalls]; 
    double[] positionY = new double[numBalls]; 
    double[] velocityX = new double[numBalls]; 
    double[] velocityY = new double[numBalls]; 
    double[] radius = new double[numBalls]; 
    double distance = 0; 

    for (int i = 0; i < numBalls; ++i) { 
     balls[i] = numBalls; 
     positionX[i] = Math.random(); 
     positionY[i] = Math.random(); 
     velocityX[i] = Math.random() * .01; 
     velocityY[i] = Math.random() * .01; 
     radius[i] = 0.05; 
    } 

    while (true) { 
     // clear the background - draw before since it is on the bottom 
     StdDraw.setPenColor(StdDraw.GRAY); 
     StdDraw.filledSquare(0, 0, 1.0); 

     // bounce off wall according to law of elastic collision 
     for (int i = 0; i < numBalls; ++i) { 

      if (Math.abs(positionX[i] + velocityX[i]) > 1.0 - radius[i]) { 
       velocityX[i] = -velocityX[i]; 
      } 
      if (Math.abs(positionY[i] + velocityY[i]) > 1.0 - radius[i]) { 
       velocityY[i] = -velocityY[i]; 
      } 
      positionX[i] = positionX[i] + velocityX[i]; 
      positionY[i] = positionY[i] + velocityY[i]; 

     //figure out the distance between 
     //if balliradius + balliradius >= distance between, then reverse direction 
     for (int j = 0; j < numBalls; ++j){//create a for loop 

      distance = Math.sqrt(Math.pow(positionX[i] - positionX[i], 2) + Math.pow(positionY[i] - positionY[i], 2)); 

      if (distance <= radius[i] + radius[i]){ //if distance between two balls has them touching/overlapping, change direction 
       positionX[i] = -positionX[i] - velocityX[i]; 
       positionY[i] = -positionY[i] - velocityY[i]; 
      } //if balliradius + balliradius < distance between, then keep moving 
      // update position 
      positionX[i] = positionX[i] + velocityX[i]; 
      positionY[i] = positionY[i] + velocityY[i]; 

      // draw ball on the screen 
      StdDraw.setPenColor(StdDraw.BLUE); 
      StdDraw.filledCircle(positionX[i], positionY[i], radius[i]); 
     } 
     // display and pause for 20 ms 
     StdDraw.show(pause); 
    } 

    } 
} 

}

Answer 1

首先，你的距离测试应包括两个对象，不只是一个（因为它的距离将始终为零）请注意使用position*[j]：

distance = Math.sqrt(Math.pow(positionX[i] - positionX[j], 2) + Math.pow(positionY[i] - positionY[j], 2)); 

您的反弹计算也是错误的。对于最简单的可能反弹，撤消最新的速度调整，然后颠倒速度分量的符号（同样，您需要访问两个对象，不只是一个，注意radius[j]）：

if (distance <= radius[i] + radius[j]){ //if distance between two balls has them touching/overlapping, change direction 
    // undo last velocity update; now the balls aren't overlapping anymore 
    positionX[i] = positionX[i] - velocityX[i] ; 
    positionY[i] = positionY[i] - velocityY[i] ; 
    positionX[j] = positionX[j] - velocityX[j] ; 
    positionY[j] = positionY[j] - velocityY[j] ; 
    // now reverse all velocity components 
    velocityX[i] = -velocityX[i] ; 
    velocityY[i] = -velocityY[i] ; 
    velocityX[j] = -velocityX[j] ; 
    velocityY[j] = -velocityY[j] ; 
    }