ThreadLocal学习1

import java.lang.ThreadLocal.ThreadLocalMap;   
import java.lang.ThreadLocal.ThreadLocalMap.Entry;   
import java.util.HashMap;   
  
public class ThreadLocalTest2 {   
  
    public ThreadLocalTest2() {   
        super();   
  
    }   
  
    /**  
     * @param args  
     */  
    public static void main(String[] args) {   
        ThreadLocal<String> t_get = Threadlocal1();   
  
        ThreadLocal<String> tl2 = new ThreadLocal<String>();   
        /*  
         * ThreadLocal是用自己的object作为map的key  
         */  
        System.out.println(tl2.get()); // null   
  
        System.out.println(t_get.get());// defg   
  
        // =======================================   
        for (int i = 0; i < 3; i++) {   
            new Thread() {   
                public void run() {   
  
                    ThreadLocalManager.init();   
                    try {   
                        /*  
                         * 保证3个线程init都执行完毕,在打出内容,发现hashMap中内容一致(被覆盖了!)  
                         */  
                        Thread.sleep(5000);   
                    } catch (InterruptedException e) {   
                        // TODO Auto-generated catch block   
                        e.printStackTrace();   
                    }   
                    System.out.println(ThreadLocalManager.threadLocal1.get());   
                    System.out.println(ThreadLocalManager.threadLocal2.get());   
                    System.out.println(ThreadLocalManager.hm.get("key"));   
			System.out.println("============");
                }   
            }.start();   
  
        }   
  
    }   
  
    public static ThreadLocal<String> Threadlocal1() {   
        ThreadLocal<String> tl1 = new ThreadLocal<String>();   
        tl1.set("abc");   
  
        ThreadLocal<String> tl2 = new ThreadLocal<String>();   
        tl2.set("defg");   
  
        return tl2;   
    }   
  
}   
  
class ThreadLocalManager {   
    public static int i = 0;   
  
    public static ThreadLocal<Integer> threadLocal1 = new ThreadLocal<Integer>();   
  
    public static ThreadLocal<Integer> threadLocal2 = new ThreadLocal<Integer>();   
  
    public static HashMap hm = new HashMap();   
  

    public static void init() {   
        threadLocal1.set(Thread.currentThread().hashCode());   

	/*
         * i++,相当于new Integer(i++);
         * 也就是说对象已经变了,每次传过去的堆上的Integer已经变了
         * 变的是引用变量的指向(static i)
         * 在线程内部调用了这个init()方法,相当于在每个线程都new Integer()
         */
        threadLocal2.set(i++);  
 	 /*
         * 这个key在hash以后在每个线程都是一样的
         * threadLocal中的map的key是线程 ,每个线程不同的
         */
        hm.put("key", i++);   
    }   
  
}   
  
/*getMap & createMap都是根据t : 当前 Thread作为参数,也就是说对于不同线程来说,这个ThreadLocalMap 是不同的  
 
static class ThreadLocalMap 是一个内部类,类似map,有一个Entry[] table构成,但是没有实现Map接口*/  
public void set(T value) {   
    Thread t = Thread.currentThread();   
    ThreadLocalMap map = getMap(t);   
    if (map != null)   
        map.set(this, value);   
    else  
        createMap(t, value);   
}   
  
  
  
/*  
 * createMap的时候,都是new一个对象ThreadLocalMap,然后把这个对象给t.threadLocals,t是当前线程(参看set方法)  
 * 因为是new 的对象,所以显然证明这个ThreadLocalMap对于每一个Thread是不同的.  
 */  
void createMap(Thread t, T firstValue) {   
    t.threadLocals = new ThreadLocalMap(this, firstValue);   
}   
  
  
/*  
 * ThreadLocalMap的构造函数传的是this - 也就是ThreadLocal对象.  
 * hash以后,用threadlocal作为key存放我们的value, Entry 数组是典型的map实现   
 */  
ThreadLocalMap(ThreadLocal firstKey, Object firstValue) {   
    table = new Entry[INITIAL_CAPACITY];   
    int i = firstKey.threadLocalHashCode & (INITIAL_CAPACITY - 1);   
    table[i] = new Entry(firstKey, firstValue);   
    size = 1;   
    setThreshold(INITIAL_CAPACITY);   
}   
  
/*  
 * get方法,注意的是 if (null = map)  setInitialValue  
 * 也就是说这个ThreadLocalMap不是我们new ThreadLocal就有个,而是调用get(),set()方法的时候才会建立的  
 * setInitialValue 返回 null !  
 */  
  
public T get() {   
    Thread t = Thread.currentThread();   
    ThreadLocalMap map = getMap(t);   
    if (map != null) {   
        ThreadLocalMap.Entry e = map.getEntry(this);   
        if (e != null)   
            return (T)e.value;   
    }   
    return setInitialValue();   
}