java练习题，每天一个java小程序-1…

JAVA练习题，能做多少就做多少。http://bbs.csdn.net/topics/110067294

这个是从CSDN看到的。每天一个吧 。

【程序10】 
题目：一球从100米高度自由落下，每次落地后反跳回原高度的一半；再落下，求它在 第10次落地时，共经过多少米？第10次反弹多高？ 

这个题目，下面我会贴出来两种代码。其实这个题目，我烦了简单计算，想搞得有趣味性一点，结果耽误了好几天时间，最后发现搞的也不好。

先第一种，为了解题而解题。

==== Main.java ====

public class Main {

private double TotalHeight = 100;

private double CurHeight = 50;

public void drop(int times) {

if ((times - 1) == 0) {

return;

}

setTotalHeight(getTotalHeight() + 2 * getCurHeight());

setCurHeight(getCurHeight() / 2);

drop(times - 1);

}

public double getTotalHeight() {

return TotalHeight;

}

public void setTotalHeight(double totalHeight) {

TotalHeight = totalHeight;

}

public double getCurHeight() {

return CurHeight;

}

public void setCurHeight(double curHeight) {

CurHeight = curHeight;

}

public static void main(String[] args) {

Main main = new Main();

main.drop(2);

System.out.println("Total height is " +main.getTotalHeight());

System.out.println("Current height is " +main.getCurHeight());

}

}

==== 然后是第二种 =====

==== Main.java ====

package main;

import javax.swing.JFrame;

import panel.BallPanel;

import time.Delay;

public class MainFrame extends JFrame {

public MainFrame(String title) {

super(title);

}

public static void main(String[] args) {

Delay delay = new Delay();

MainFrame frame = new MainFrame("Hello JFrame");

BallPanel ballPanel = new BallPanel();

frame.add(ballPanel);

frame.setSize(500, 500);

frame.setVisible(true);

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

delay.initDelay();

ballPanel.setDelay(delay.getDelay());

ballPanel.loopDrop(0);

}

}

==== Delay.java ====

package time;

public class Delay {

public void initDelay() {

int g = 10;

int i = 0;

double s, t, t0 = 0.0;

delay = new int[100];

for (s = 100; s < 10100; s += 100) {

t = Math.sqrt(2 * s / g);

delay[i++] = (int) ((t - t0) * 100);

t0 = t;

}

}

public int[] getDelay() {

return delay;

}

private int delay[];

}

==== BallPanel.java ====

package panel;

import java.awt.Color;

import java.awt.Graphics;

import javax.swing.JPanel;

public class BallPanel extends JPanel {

public BallPanel() {

super();

}

public void paint(Graphics g) {

g.clearRect(0, 0, this.getWidth(), this.getHeight());

g.setColor(Color.BLUE);

g.fillOval(250, ballCenter, 30, 30);

}

public void loopDrop(int height) {

int i;

if (this.height == height) { // At bottom

for (i = 0; i < targetHeight; i += MUL) {

ballCenter = this.height - i;

this.repaint();

try {

Thread.sleep(delay[(targetHeight - i - 1) / MUL]);

} catch (InterruptedException e) {

e.printStackTrace();

}

}

loopDrop(this.height - i);

} else { // At top

for (i = height; i < this.height; i += MUL) {

ballCenter = i;

this.repaint();

try {

Thread.sleep(delay[(i - height) / MUL]);

} catch (InterruptedException e) {

e.printStackTrace();

}

}

targetHeightV = targetHeightV / 2;

targetHeight = targetHeightV;

if (targetHeight != 0) {

loopDrop(i);

}

}

}

public void setDelay(int delay[]) {

this.delay = delay;

}

private int extracted() {

return 100 * MUL;

}

private int targetHeight = extracted();

private int targetHeightV = extracted();

private int ballCenter = 0;

private int height = extracted();

private int delay[];

private final int MUL = 4;

}

其实所谓的第二种，是用的JFrame在JPanel上画图，直观的展示出来每次弹起来的效果。因为100像素实在太小了，所以我做了一个变量MUL，相当于是等比例扩大的效果。问题就是弹不到10次距离就用光了，所以。。。。。权当娱乐了。。当然可以等比例在放大，例如100M看成是10000像素，这样能多弹几次。这个程序，最后球就在那里不动了，程序不会自己退出。