java多线程递增计数

有多个线程，每个线程随机访问一个变量，无论谁获取访问权，变量都会递增，当变量值到达30后，线程终止。

public class ThreadTest extends Thread{

//变量上线值
public final static int NUM = 30;
//计数值
public static int count = 0;
//加锁
private static byte[] lock = new byte[0];

@Override
public void run() {
while (true) {
synchronized (lock) {
if (count >= ThreadTest.NUM)
return;
count++;
System.out.println("线程"+this.getName()+"----"+count);
}
}

}

public ThreadTest(String threadName) {
super(threadName);
}

public static void main(String[] args) {
List<ThreadTest> list = new ArrayList<ThreadTest>();

for (int i = 1; i <= 5; i++)
{
ThreadTest my = new ThreadTest("Thrad " + i);
my.start();
list.add(my);
}
try
{
for (ThreadTest my : list)
{
my.join();
}
}
catch (InterruptedException e)
{
e.printStackTrace();
}
System.out.println("Over.");
}
}

执行结果
线程Thrad 1----1

线程Thrad 1----2

线程Thrad 1----3

线程Thrad 1----4

线程Thrad 1----5

线程Thrad 2----6

线程Thrad 2----7

线程Thrad 2----8

线程Thrad 2----9

线程Thrad 2----10

线程Thrad 2----11

线程Thrad 2----12

线程Thrad 2----13

线程Thrad 2----14

线程Thrad 2----15

线程Thrad 2----16

线程Thrad 1----17

线程Thrad 1----18

线程Thrad 1----19

线程Thrad 1----20

线程Thrad 1----21

线程Thrad 1----22

线程Thrad 1----23

线程Thrad 1----24

线程Thrad 1----25

线程Thrad 1----26

线程Thrad 1----27

线程Thrad 1----28

线程Thrad 1----29

线程Thrad 1----30

Over.