这是两个简单的小项目，产生两个在重力的作用下产生运动的自由落体的小球，模拟简单的自由落体和平抛运动，可以用在教学演示中

建立小球

import java.awt.Color;

public class Ball {

// 圆心坐标

private int x, y;

private int speedX, speedY;

public static final int WIDTH = 20;

public static final int HALF_WIDTH = WIDTH >> 1;

public static final int G = 1;

public Ball(int x, int y, int speedX, int speedY) {

super();

this.x = x;

this.y = y;

this.speedX = speedX;

this.speedY = speedY;

}

public Ball() {

}

public void draw(Graphics g) {

g.setColor(Color.WHITE);

g.fillOval(x - HALF_WIDTH, y - HALF_WIDTH, WIDTH, WIDTH);

logic();

}

private void logic() {

x += speedX;

y += speedY;

speedY += G;

// 触底反弹

if (y >= BallFrame.FRAME_HEIGHT - HALF_WIDTH) {

y = BallFrame.FRAME_HEIGHT - HALF_WIDTH;

speedY -= 4;

speedY = - speedY;

if(speedY >0)

speedY = 0;

}

}

public int getX() {

return x;

}

public void setX(int x) {

this.x = x;

}

public int getY() {

return y;

}

public void setY(int y) {

this.y = y;

}

public int getSpeedX() {

return speedX;

}

public void setSpeedX(int speedX) {

this.speedX = speedX;

}

public int getSpeedY() {

return speedY;

}

public void setSpeedY(int speedY) {

this.speedY = speedY;

}

}

建立java窗口

import java.awt.Color;

import java.awt.Frame;

import java.awt.event.WindowAdapter;

import java.awt.event.WindowEvent;

public class BallFrame extends Frame implements Runnable{

public static final int FRAME_WIDTH = 800;

public static final int FRAME_HEIGHT = 200;

private Ball ball1;

private Ball ball2;

public BallFrame() {

setTitle("调皮的小球");

setSize(FRAME_WIDTH, FRAME_HEIGHT);

setLocation(200, 100);

setResizable(false);

initBalls();

initWindowListener();

setVisible(true);

new Thread(this).start();

}

private void initBalls(){

ball1 = new Ball(100, 20, 0, 0);

ball2 = new Ball(20, 20, 5, 0);

}

private void initWindowListener() {

addWindowListener(new WindowAdapter() {

@Override

public void windowClosing(WindowEvent e) {

System.exit(0);

}

});

}

@Override

public void paint(Graphics g) {

g.fillRect(0, 0, FRAME_WIDTH, FRAME_HEIGHT);

//ball1.draw(g);

ball2.draw(g);

}

@Override

public void run() {

try {

while(true){

Thread.sleep(30);

repaint();

}

} catch (InterruptedException e) {

e.printStackTrace();

}

}

}

调用主方法

public class MyGame {

public static void main(String[] args) {

new BallFrame();

}

}