JAVA多线程变量的深入认识(三)

现在的问题来了，当我们关注例子I，希望共享类RunInstance，即

    RunInstance t = new RunInstance();

        Thread t1 = new Thread(t);

        Thread t2 = new Thread(t);

却又要对变量进行线程单独化的管理时，怎么办？这时候就有了ThreadLocal。请看

例子III

首先我们对类TestInstance做一下改造，也就是把Flag变成ThreadLocal，即线程的独自变量

改造如下1,2,3点，接着我们仍旧运行例子I

class TestInstance {

    static Integer count = 0;

    //1: public int flag = 0;

    public ThreadLocal flag = new ThreadLocal(){

        public Integer initialValue(){

            return 0;

        }

    };

    public void runtest(){

    //2:  if (flag ==0)m1();  

        if (flag.get() ==0)m1();  

        else   m2();

        }

    public  void m1(){

    //3.  flag=1;

        flag.set(1);

        synchronized(count){

        for(int i = 0;i < 10; i++){

            count++;   

            System.out.println(Thread.currentThread().getName()+": m1's printing : count = "+count);  

            }

        }

    }

    public void m2(){

        synchronized(count){    

            for(int i = 0;i < 10; i++){

                count++;  

                System.out.println(Thread.currentThread().getName()+": m2's printing : count = "+count);  

            }  

        }

    }

}

却发现结果发生了变化。两个线程都只执行了m1，也就是说flag是

线程独立的。

Thread-0: m1's printing : count = 2

Thread-1: m1's printing : count = 2

Thread-0: m1's printing : count = 3

Thread-1: m1's printing : count = 4

Thread-0: m1's printing : count = 5

Thread-1: m1's printing : count = 6

Thread-0: m1's printing : count = 7

Thread-1: m1's printing : count = 8

Thread-0: m1's printing : count = 9

Thread-1: m1's printing : count = 10

Thread-0: m1's printing : count = 11

Thread-1: m1's printing : count = 12

Thread-0: m1's printing : count = 13

Thread-1: m1's printing : count = 14

Thread-0: m1's printing : count = 15

Thread-1: m1's printing : count = 16

Thread-0: m1's printing : count = 17

Thread-1: m1's printing : count = 18

Thread-0: m1's printing : count = 19

Thread-1: m1's printing : count = 20