java语言中的线程

   每一个java程序中都至少有一个线程。当java程序运行时，JVM就会创建主线程，并在该线程中调用程序的main()方法。线程可以理解为程序内部独立的运行单位。线程包括单线程模式和多线程模式，在单线程模式，只能一个方法调用执行完毕后，才会执行到下一个方法的调用，而多线程模式能够同时调用执行多个方法。
   
   线程与进程的区别：一个应用程序就是一个进程，而线程是一个进程内部的多个运行单位。

   线程的启动是通过调用线程的start()方法启动。
   线程的运行是从线程的run()方法开始。

/*启动一个线程，能够添加多个小球，并且能够运行，
*小球之间能够相互碰撞，小球在窗体边缘能够反弹，
*能够暂停小球，和继续，还能够结束进程。
  */
package com.xiancheng071201;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class Game {

private JPanel centerPanel;
private Ball ba;
private ArrayList<Ball> al = new ArrayList<Ball>(); //创建队列对象

public void UI(){
JFrame jf = new JFrame("线程");

jf.setLayout(new BorderLayout());   //边框布局
JPanel jp=new JPanel();             //创建面板对象
jp.setPreferredSize(new Dimension(90, 0));  //给面板设置大小


jf.setSize(800, 500);

JButton jb = new JButton("添加小球");  //把按钮添加到面板上
jp.add(jb);
JButton jb1 = new JButton(" 暂    停   ");
jp.add(jb1);
JButton jb2 = new JButton("重新开始");
jp.add(jb2);
JButton jb3 = new JButton("  结     束  ");
jp.add(jb3);

jp.setBackground(Color.BLUE);    //给面板设置背景颜色
jf.add(jp, BorderLayout.WEST);   //把面板添加到窗体上，并设置添加位置

centerPanel=new JPanel();   //设置中央面板
centerPanel.setBackground(new Color(235,235,235));  //给中央面板设置背景颜色

jf.add(centerPanel, BorderLayout.CENTER);//把中央面板添加到窗体上

jf.setDefaultCloseOperation(3);   //关闭窗体时，程序退出
jf.setVisible(true);       //把窗体显示出来

jb.addActionListener(l);     //给按钮添加事件监听器
jb1.addActionListener(l);
jb2.addActionListener(l);
jb3.addActionListener(l);


Graphics g = centerPanel.getGraphics();       //创建中央面板画布对象

ImageIcon icon = new ImageIcon("beijing.jpg"); //创建图片对象
g.drawImage(icon.getImage(), 0, 0, null);      //把图片画到中央面板上

while(true){
try {
Thread.sleep(30);
} catch (InterruptedException e) {

e.printStackTrace();
}
//创建内存存储画布对象
BufferedImage buffer = new BufferedImage(
centerPanel.getWidth(), centerPanel.getHeight(),
BufferedImage.TYPE_INT_RGB);
Graphics g2 = buffer.getGraphics();
g2.drawImage(icon.getImage(),0, 0,
buffer.getWidth(),buffer.getHeight(),null);


for(int i = 0; i<al.size();i++){
Ball ba = al.get(i);
ba.Drawball(g2);
}
g.drawImage(buffer, 0, 0, null);

}


}
ActionListener l = new ActionListener() {


public void actionPerformed(ActionEvent e) {

String cmd = e.getActionCommand();

if(cmd.equals("添加小球")){
   ba = new Ball(centerPanel,al);
   al.add(ba);
   ba.start();
}
if(cmd.equals(" 暂    停   ")){
for(int i=0;i<al.size();i++){
     Ball ba = al.get(i);
     ba.setPauseflag(true);
}
}
if(cmd.equals("重新开始")){
for(int i=0;i<al.size();i++){
Ball ba = al.get(i);
   ba.setPauseflag(false);
}
}
if(cmd.equals("  结     束  ")){
while(!al.isEmpty()){
Ball ba = al.remove(0);
ba.setStopflag(true);
}
// for(int i=0;i<al.size();i++){
// Ball ba = al.get(i);
//    ba.setStopflag(true);
// }
}
}
};
public static void main(String[] args){
Game ga = new Game();
ga.UI();
}

}



package com.xiancheng071201;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.util.ArrayList;
import java.util.Random;

import javax.swing.JPanel;

public class Ball extends Thread{


private ArrayList<Ball> al;
private JPanel centerPanel;
private Graphics g;
private int x, y, oldx, oldy, radius, vx, vy, k,t,p;
private boolean pauseflag = false;
private boolean stopflag = false;
private int xx;
private int yy;


public Ball(JPanel centerPanel,ArrayList<Ball> al) {
this.centerPanel = centerPanel;
this.al = al;
init();
}

    public void setPauseflag(boolean pauseflag) {
this.pauseflag = pauseflag;
}
   
public void setStopflag(boolean stopflag) {
this.stopflag = stopflag;
}

public void run(){
    while(true){
    try {
Thread.sleep(30);
} catch (InterruptedException e) {
e.printStackTrace();
}
    g = centerPanel.getGraphics();
//    g = (Graphics2D)gg;
// //设置抗锯齿效果
// g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
// RenderingHints.VALUE_ANTIALIAS_ON);

    if(pauseflag){
    continue;
    }
   
//    clearball();
   
    rebound();
   
    if(stopflag){
    for(int i=0;i<al.size();i++){
   Ball ba = al.get(i);
      ba.clearball();
   }
    break;
    }
   
//    Drawball();
    }
    }
    //初始化
    public void init(){
    Random r = new Random();
k = r.nextInt(4);
t = r.nextInt(4);
p = r.nextInt(4);
radius = r.nextInt(20)+20;
vx = r.nextInt(5)+2;
vy = r.nextInt(5)+2;
    }
   

    //反弹
    public void rebound(){
   
    oldx = x;
    oldy = y;
   
    x += vx;
    crash(1);
y += vy;
crash(2);
if(x <= 0){
vx = Math.abs(vx);
}
if(x + radius >= centerPanel.getWidth()){
vx = -Math.abs(vx);
}
if(y <= 0){
vy = Math.abs(vy);
}
if(y + radius >= centerPanel.getHeight()){
vy = -Math.abs(vy);
}



    }
   
     //清除
    public void clearball(){
    for(int i=radius*2; i>0; i--){
       g.setColor(centerPanel.getBackground());
           g.fillOval(x-i/4, y-i/2, i, i);
      }
    }
   
    //画球
    public void Drawball(Graphics g){
    for(int i=radius*2; i>0; i--){
    Color c = new Color(255-i*k, 255-i*t, 255-i*p);
          g.setColor(c);
      g.fillOval(x-i/4, y-i/2, i, i);
    }
    }
    //碰撞
public boolean crash(int direction){
for(int i=0;i<al.size();i++){
Ball ba = al.get(i);
if(ba == this){
continue;
}

   xx = x + radius;
   yy = y + radius;

//比较圆心的距离
int benx = Math.abs(ba.xx - this.xx);
int beny = Math.abs(ba.yy - this.yy);

int ben = (int) Math.sqrt(benx*benx + beny*beny);

if(ben <= ba.radius + this.radius){
System.out.println("碰撞了！！！！！");
if(direction == 1){
vx = -vx;
}
if(direction == 2){
vy = -vy;
}
x = oldx;
y = oldy;
}
}
return false;
}
}