问一个关于线程的问题，一直不是弄的很清楚！
package   com.pos.test;

public   class   SimpleThread   extends   Thread   {
public   int   countDown   =   5;
private   static   int   threadCount   =   0;
private   int   threadNumber   =   ++threadCount;
public   SimpleThread(){
System.out.println( "making   "+threadNumber);
}

public   void   run(){
while(true){
System.out.println( "thread "+threadNumber+ "( "+countDown+ ") ");
if(--countDown==0)   return;
}
}
/**
  *   @param   args
  */
public   static   void   main(String[]   args)   {
for(int   i   =0;i <5;i++)
new   SimpleThread().start();
System.out.println( "end ");

}

}
这是thinkinjava的原程序，运行是正常的，下面是我改的程序，问什么就发生了并发的问题，刚开始学习线程，对同一个类实例化的线程对象是否共享一块内存，是否每个对象中的变量相互独立弄的不是很清楚，希望有知道的能给我一点帮助！

public   class   SimpleThread   implements   Runnable   {
public   int   countDown   =   5;
private   static   int   threadCount   =   0;
private   int   threadNumber   =   ++threadCount;
public   SimpleThread(){
System.out.println( "making   "+threadNumber);
}

public   void   run(){
while(true){
System.out.println( "thread "+threadNumber+ "( "+countDown+ ") ");
if(--countDown==0)   return;
}
}
/**
  *   @param   args
  */
public   static   void   main(String[]   args)   {
SimpleThread   st   =   new   SimpleThread();
for(int   i   =0;i <5;i++)

new   Thread(st).start();
System.out.println( "end ");

}

}


------解决方案--------------------
把你第二个程序改了一下：
package com.whj.jdk.lang;

public class SimpleThread extends Thread {
private static int threadCount = 0;

/**
* @param args
*/
public static void main(String[] args) {

SimpleThread st = new SimpleThread(); // Error Code
for (int i = 0; i < 5; i++) {
// new SimpleThread().start();
new Thread(st).start(); // Error Code
}
System.out.println( "end ");

}

public int countDown = 5;

private final int threadNumber = ++threadCount;

public SimpleThread() {
System.out.println( "making " + threadNumber);
}

@Override
public void run() {
while (true) {
System.out.println( "thread " + threadNumber + "( " + countDown + ") ");
if (--countDown == 0) {
System.out.println( "GO ");
return;
}
}
}

}

运行后的输出结果是：
making 1
end
thread1(5)
thread1(4)
thread1(3)
thread1(2)
thread1(1)
GO
thread1(0)
thread1(-1)
thread1(-2)
thread1(-3)
thread1(-4)
thread1(-5)
thread1(-6)
thread1(-7)
thread1(-8)
thread1(-9)
thread1(-10)
thread1(-11)
thread1(-12)
thread1(-13)
thread1(-14)

以下被我中断。

你仔细分析一下就知道为什么了。
------解决方案--------------------