package animal;
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public class Animal {
String name="动物";
public void printInfo(){
System.out.println(name);
}
}
package animal;
public class Bird extends Animal{
String name="bird";
@Override
public void printInfo(){
System.out.println("我是："+name);
}
}
package animal;
public class Fish extends Animal{
String name="fish";
@Override
public void printInfo(){
System.out.println("我是："+name);
}
}
package animal;
public class Test {
public static void main(String[] args) {
Animal bird=new Bird();
bird.printInfo();
Animal fish=new Fish();
fish.printInfo();
}
}
表1. CheckerDrag.java
// CheckerDrag.javaimport java.awt.*;import java.awt.event.*;public class CheckerDrag extends java.applet.Applet{ // Dimension of checkerboard square. // 棋盘上每个小方格的尺寸 final static int SQUAREDIM = 40; // Dimension of checkerboard -- includes black outline. // 棋盘的尺寸 – 包括黑色的轮廓线 final static int BOARDDIM = 8 * SQUAREDIM + 2; // Dimension of checker -- 3/4 the dimension of a square. // 棋子的尺寸 – 方格尺寸的3/4 final static int CHECKERDIM = 3 * SQUAREDIM / 4; // Square colors are dark green or white. // 方格的颜色为深绿色或者白色 final static Color darkGreen = new Color (0, 128, 0); // Dragging flag -- set to true when user presses mouse button over checker // and cleared to false when user releases mouse button. // 拖动标记 --当用户在棋子上按下鼠标按键时设为true， // 释放鼠标按键时设为false boolean inDrag = false; // Left coordinate of checkerboard's upper-left corner. // 棋盘左上角的左方向坐标 int boardx; // Top coordinate of checkerboard's upper-left corner. //棋盘左上角的上方向坐标 int boardy; // Left coordinate of checker rectangle origin (upper-left corner). // 棋子矩形原点(左上角)的左方向坐标 int ox; // Top coordinate of checker rectangle origin (upper-left corner). // 棋子矩形原点(左上角)的上方向坐标 int oy; // Left displacement between mouse coordinates at time of press and checker // rectangle origin. // 在按键时的鼠标坐标与棋子矩形原点之间的左方向位移 int relx; // Top displacement between mouse coordinates at time of press and checker // rectangle origin. // 在按键时的鼠标坐标与棋子矩形原点之间的上方向位移 int rely; // Width of applet drawing area. // applet绘图区域的宽度 int width; // Height of applet drawing area. // applet绘图区域的高度 int height; // Image buffer. // 图像缓冲 Image imBuffer; // Graphics context associated with image buffer. // 图像缓冲相关联的图形背景 Graphics imG; public void init () { // Obtain the size of the applet's drawing area. // 获取applet绘图区域的尺寸 width = getSize ().width; height = getSize ().height; // Create image buffer. // 创建图像缓冲 imBuffer = createImage (width, height); // Retrieve graphics context associated with image buffer. // 取出图像缓冲相关联的图形背景 imG = imBuffer.getGraphics (); // Initialize checkerboard's origin, so that board is centered. // 初始化棋盘的原点，使棋盘在屏幕上居中 boardx = (width - BOARDDIM) / 2 + 1; boardy = (height - BOARDDIM) / 2 + 1; // Initialize checker's rectangle's starting origin so that checker is // centered in the square located in the top row and second column from // the left. // 初始化棋子矩形的起始原点，使得棋子在第一行左数第二列的方格里居中 ox = boardx + SQUAREDIM + (SQUAREDIM - CHECKERDIM) / 2 + 1; oy = boardy + (SQUAREDIM - CHECKERDIM) / 2 + 1; // Attach a mouse listener to the applet. That listener listens for // mouse-button press and mouse-button release events. // 向applet添加一个用来监听鼠标按键的按下和释放事件的鼠标监听器 addMouseListener (new MouseAdapter () { public void mousePressed (MouseEvent e) { // Obtain mouse coordinates at time of press. // 获取按键时的鼠标坐标 int x = e.getX (); int y = e.getY (); // If mouse is over draggable checker at time // of press (i.e., contains (x, y) returns // true), save distance between current mouse // coordinates and draggable checker origin // (which will always be positive) and set drag // flag to true (to indicate drag in progress). // 在按键时如果鼠标位于可拖动的棋子上方 // （也就是contains (x, y)返回true），则保存当前 // 鼠标坐标与棋子的原点之间的距离（始终为正值）并且 // 将拖动标志设为true（用来表明正处在拖动过程中） if (contains (x, y)) { relx = x - ox; rely = y - oy; inDrag = true; } } boolean contains (int x, int y) { // Calculate center of draggable checker. // 计算棋子的中心位置 int cox = ox + CHECKERDIM / 2; int coy = oy + CHECKERDIM / 2; // Return true if (x, y) locates with bounds // of draggable checker. CHECKERDIM / 2 is the // radius. // 如果(x, y)仍处于棋子范围内则返回true // CHECKERDIM / 2为半径 return (cox - x) * (cox - x) + (coy - y) * (coy - y) CHECKERDIM / 2 * CHECKERDIM / 2; } public void mouseReleased (MouseEvent e) { // When mouse is released, clear inDrag (to // indicate no drag in progress) if inDrag is // already set. // 当鼠标按键被释放时，如果inDrag已经为true， // 则将其置为false（用来表明不在拖动过程中） if (inDrag) inDrag = false; } }); // Attach a mouse motion listener to the applet. That listener listens // for mouse drag events. //向applet添加一个用来监听鼠标拖动事件的鼠标运动监听器 addMouseMotionListener (new MouseMotionAdapter () { public void mouseDragged (MouseEvent e) { if (inDrag) { // Calculate draggable checker's new // origin (the upper-left corner of // the checker rectangle). // 计算棋子新的原点（棋子矩形的左上角） int tmpox = e.getX () - relx; int tmpoy = e.getY () - rely; // If the checker is not being moved // (at least partly) off board, // assign the previously calculated // origin (tmpox, tmpoy) as the // permanent origin (ox, oy), and // redraw the display area (with the // draggable checker at the new // coordinates). // 如果棋子（至少是棋子的一部分）没有被 // 移出棋盘，则将之前计算的原点 // (tmpox, tmpoy)赋值给永久性的原点(ox, oy)， // 并且刷新显示区域（此时的棋子已经位于新坐标上） if (tmpox boardx tmpoy boardy tmpox + CHECKERDIM boardx + BOARDDIM tmpoy + CHECKERDIM boardy + BOARDDIM) { ox = tmpox; oy = tmpoy; repaint (); } } } }); } public void paint (Graphics g) { // Paint the checkerboard over which the checker will be dragged. // 在棋子将要被拖动的位置上绘制棋盘 paintCheckerBoard (imG, boardx, boardy); // Paint the checker that will be dragged. // 绘制即将被拖动的棋子 paintChecker (imG, ox, oy); // Draw contents of image buffer. // 绘制图像缓冲的内容 g.drawImage (imBuffer, 0, 0, this); } void paintChecker (Graphics g, int x, int y) { // Set checker shadow color. // 设置棋子阴影的颜色 g.setColor (Color.black); // Paint checker shadow. // 绘制棋子的阴影 g.fillOval (x, y, CHECKERDIM, CHECKERDIM); // Set checker color. // 设置棋子颜色 g.setColor (Color.red); // Paint checker. // 绘制棋子 g.fillOval (x, y, CHECKERDIM - CHECKERDIM / 13, CHECKERDIM - CHECKERDIM / 13); } void paintCheckerBoard (Graphics g, int x, int y) { // Paint checkerboard outline. // 绘制棋盘轮廓线 g.setColor (Color.black); g.drawRect (x, y, 8 * SQUAREDIM + 1, 8 * SQUAREDIM + 1); // Paint checkerboard. // 绘制棋盘 for (int row = 0; row 8; row++) { g.setColor (((row 1) != 0) ? darkGreen : Color.white); for (int col = 0; col 8; col++) { g.fillRect (x + 1 + col * SQUAREDIM, y + 1 + row * SQUAREDIM, SQUAREDIM, SQUAREDIM); g.setColor ((g.getColor () == darkGreen) ? Color.white : darkGreen); } } } // The AWT invokes the update() method in response to the repaint() method // calls that are made as a checker is dragged. The default implementation // of this method, which is inherited from the Container class, clears the // applet's drawing area to the background color prior to calling paint(). // This clearing followed by drawing causes flicker. CheckerDrag overrides // update() to prevent the background from being cleared, which eliminates // the flicker. // AWT调用了update()方法来响应拖动棋子时所调用的repaint()方法。该方法从 // Container类继承的默认实现会在调用paint()之前，将applet的绘图区域清除 // 为背景色，这种绘制之后的清除就导致了闪烁。CheckerDrag重写了update()来 // 防止背景被清除，从而消除了闪烁。 public void update (Graphics g) { paint (g); }}
import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.awt.image.*;
import java.awt.geom.*;
import java.util.*;
class Car{
Image img;
int x, y;
Dimension dim;
Car(Image img){
this.img=img;
}
Car(Image img, int x, int y){
this.img=img; this.x=x; this.y=y;
}
Car(Image img, int x, int y, Dimension dim){
this(img, x, y);
this.dim=dim;
}
void draw(Graphics g, ImageObserver observer){
g.drawImage(img, x, y, observer);
}
int getX(){ return x;}
int getY(){ return y;}
void setX(int x){this.x=x;}
void setY(int y){this.y=y;}
void setLocation(int x, int y){
this.x=x; this.y=y;
}
int getWidth(){ return img.getWidth(null);}
int getHeight(){ return img.getHeight(null);}
Rectangle2D getRectangle(){
return new Rectangle2D.Float(x, y, getWidth(), getHeight());
}
void move(int dx, int dy){
x+=dx;
y+=dy;
if(dim!=null){
if(x0)x=0;
if(x+getWidth()dim.getWidth())
x=(int)dim.getWidth()-getWidth();
}
}
boolean intersects(Car car){
return getRectangle().intersects(car.getRectangle());
}
boolean intersects(int x, int y){
return getRectangle().intersects(x, y, getWidth(), getHeight());
}
}
public class CarRace extends Applet implements KeyListener, Runnable{
Image buff;
Canvas screen;
Graphics2D gs, gb;
Car redCar;
Car[] enemy=new Car[20];
Button bStart;
Thread game;
boolean loop=true;
Dimension dim=new Dimension(200, 300);
int road;
Random rnd=new Random();
public void init(){
prepareResource();
setBackground(Color.blue);
initScreen();
add(screen);
bStart=new Button("霸烙 矫累");
add(bStart);
bStart.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent ae){
screen.requestFocus();
if(!game.isAlive())
game.start();
}
});
}
void prepareResource(){
Image imgRed=getImage(getCodeBase(),"images/red_car.gif");
Image imgBlue=getImage(getCodeBase(),"images/blue_car.gif");
Image imgGreen=getImage(getCodeBase(),"images/green_car.gif");
MediaTracker mt=new MediaTracker(this);
try{
mt.addImage(imgRed, 0);
mt.addImage(imgBlue, 1);
mt.addImage(imgGreen, 2);
mt.waitForAll();
}catch(Exception e){}
buff=createImage((int)dim.getWidth(), (int)dim.getHeight());
gb=(Graphics2D)buff.getGraphics();
redCar=new Car(imgRed, 80,250, dim);
for(int i=0;i10;i++){
enemy[i]=new Car(imgBlue, 0, 0);
}
for(int i=10;ienemy.length;i++){
enemy[i]=new Car(imgGreen, 0, 0);
}
for(int i=0;ienemy.length;i++){
setEnemy(i);
}
game=new Thread(this);
}
public void stop(){
loop=false;
}
public void run(){
while(loop){
drawScreen();
try{ Thread.sleep(50);}catch(Exception e){}
}
}
void initScreen(){
screen=new Canvas(){
public void paint(Graphics g){
if(gs==null){
gs=(Graphics2D)screen.getGraphics();
}
drawScreen();
}
};
screen.setSize(dim);
screen.addKeyListener(this);
}
void setEnemy(int en){
int x, y;
next:while(true){
x=rnd.nextInt((int)dim.getWidth()-enemy[en].getWidth());
y=-rnd.nextInt(5000)-200;
for(int j=0;jenemy.length;j++){
if(j!=en enemy[j].intersects(x, y))continue next;
}
enemy[en].setLocation(x, y);
break;
}
}
void check(Car en){
if(redCar.intersects(en)){
if(redCar.getX()en.getX()){
en.move(-20, 0);
redCar.move(20, 0);
}
else{
en.move(20,0);
redCar.move(-20, 0);
}
}
}
synchronized void drawScreen(){
gb.clearRect(0, 0, (int)dim.getWidth(), (int)dim.getHeight());
gb.setPaint(new Color(100, 100, 100));
gb.fillRect(0, 0, (int)dim.getWidth(), (int)dim.getHeight());
drawRoad();
for(int i=0;ienemy.length;i++){
enemy[i].move(0, 15);
enemy[i].draw(gb, screen);
if(enemy[i].getY()dim.getHeight())
setEnemy(i);
check(enemy[i]);
}
redCar.draw(gb, screen);
gs.drawImage(buff, 0,0, screen);
}
void drawRoad(){
road+=80;
gb.setPaint(Color.yellow);
gb.fillRect((int)dim.getWidth()/2, road,10,150);
if(road=dim.getHeight())road=-150;
}
public void keyPressed(KeyEvent ke){
if(ke.getKeyCode()==KeyEvent.VK_LEFT){
redCar.move(-10,0);
}
else if(ke.getKeyCode()==KeyEvent.VK_RIGHT){
redCar.move(10,0);
}
}
public void keyReleased(KeyEvent ke){}
public void keyTyped(KeyEvent ke){}
}
这个是一个典型的Applet,文件名应该是CarRace.java,需要图片作为车子等等,本人也是别人给的,但是还要个.html文件来运行它,代码为:
Applet code="CarRace.class" width=250 height=350
/Applet
请楼主采纳
你说的如果是javaswing程序，有两种方法，1、JPanel上放背景；2、JLabel放背景//初始化窗口publicvoidinitFrame(){//利用JPanel添加背景图片GImage=newJPanel(){protectedvoidpaintComponent(Graphicsg){ImageIconicon=n
你不理解不是因为代码的问题，而是你的数学能力：
比如给你举个例子 888 = 8*100+8*10+8
第一次循环时 sum = 0+item = 8； 而 item = item*10+a 就赋值为88了
所以第二次循环的时候 sum = 8了，那么执行sum+item 就是 8 + 88； 并且赋值给sum
并且调整item = 88*10+a = 880+8，所以item就变为888了。
以此类推。每循环一次把item的阶数（十进制）加一再加上8
就算得最后结果了。
idea中文导出java源代码方法：
1、进入idea，打开项目的projectstructure。
2、鼠标右键项目名称，选择openmodulesettings。
3、点击菜单fileprojectstructure。
4、在projectstructure中选择artifacts，点击add，选择JARFrommoduleswithdependencies。
5、进行相关的配置，即可导出java源代码。