Question

在iTunes U上发布的CS106A课程第10讲中，老师向班级展示了一个弹跳球项目。我稍微摆弄它，以便球从屏幕开始时以相同的y值返回，但由于某种原因，一旦球变得非常低，它就永远不会停止弹跳，有时反弹甚至比它更高。之前的反弹是没有意义的，因为它应该始终降低。这是代码：

import acm.program.*;
import acm.graphics.*;

public class bouncingBall extends GraphicsProgram {

int setupCount = 0;
/** Size (diameter) of the ball */
private static final int DIAM_BALL = 30;

/**
 * Amount Y velocity is increased each cycle as a result of gravity
 */
private static final double GRAVITY = 3;

/** Animation delay or pause time between ball moves */
private static final int DELAY = 50;

/** Initial X and Y location of ball */
private static final double X_START = DIAM_BALL / 2;
private static final double Y_START = 100;

/** X Velocity */
private static final double X_VEL = 5;

/** Amount Y Velocity is reduced when it bounces */
private static final double BOUNCE_REDUCE = 0.95;

/** Starting X and Y Velocities */
private double xVel = X_VEL;
private double yVel = 0.0;

/* private instance variable */
private GOval ball;

public void run() {
    while (true) {
        setup();
    // Simulation ends when ball goes off right hand
    // end of screen
    while (ball.getX() < getWidth()) {
        moveBall();
        checkForCollision();
        pause(DELAY);
    }
    }
}

/** Create and place ball. */
private void setup() {
    if(setupCount==0) {
    ball = new GOval(X_START, Y_START, DIAM_BALL, DIAM_BALL);
    ball.setFilled(true);
    add(ball);
    setupCount += 1;
}
    else {
        double tempY = ball.getY();
        ball.setBounds(X_START, tempY, DIAM_BALL, DIAM_BALL );
    }
}   

/** Update and move ball */
private void moveBall() {
    // increase yVelocity due to gravity on each cycle
    yVel += GRAVITY;
    ball.move(xVel, yVel);
}

/**
 * Determine if collision with floor, update velocities and location as
 * appropriate.
 */
private void checkForCollision() {
    // determine if ball has dropped below the floor
    if (ball.getY() > getHeight() - DIAM_BALL) {

        // change ball's Y velocity to now bounce upwards
        yVel = -yVel * BOUNCE_REDUCE;

        // assume bounce will move ball an amount above the
        // floor equal to the amount it would have dropped
        // below the floor.
        double diff = ball.getY() - (getHeight() - DIAM_BALL);
        ball.move(0, -2 * diff);
    }
}

}

注意：我对Java很新，所以请不要给我一个非常复杂的解释。谢谢！

Answer 1

我认为这是由于checkCollisions（）

下的两行

        double diff = ball.getY() - (getHeight() - DIAM_BALL);
    ball.move(0, -2 * diff);

当球非常接近地板时的圆角误差可能会导致这些线条使球跳跃。尝试删除它们。

祝你好运！

斯坦福CS106A Bouncing Ball计划不会停止弹跳？

1 个答案: