public class ThreadLocalDemo {
 
    //創(chuàng)建一個(gè)ThreadLocal對(duì)象,用來為每個(gè)線程會(huì)復(fù)制保存一份變量,實(shí)現(xiàn)線程封閉
    private  static ThreadLocal<Integer> localNum = new ThreadLocal<Integer>(){
        @Override
        protected Integer initialValue() {
            return 1;
        }
    };
 
    public static void main(String[] args) {
          //線程0
          new Thread(){
              @Override
              public void run() {
                   localNum.set(1);
                  try {
                      Thread.sleep(2000);
                  } catch (InterruptedException e) {
                      e.printStackTrace();
                  }
                  localNum.set(localNum.get()+10);
                  System.out.println(Thread.currentThread().getName()+":"+localNum.get());//11
              }
          }.start();
        //線程1
        new Thread(){
            @Override
            public void run() {
                localNum.set(3);
                try {
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                localNum.set(localNum.get()+20);
                System.out.println(Thread.currentThread().getName()+":"+localNum.get());//23
            }
        }.start();
        
        System.out.println(Thread.currentThread().getName()+":"+localNum.get());//0
    }
}

public void set(T value) {
    //拿到當(dāng)前線程
    Thread t = Thread.currentThread();
    //拿到當(dāng)前線程map
    ThreadLocalMap map = getMap(t);
    if (map != null)
        //存在設(shè)置值
        map.set(this, value);
    else
        //不存在則創(chuàng)建
        createMap(t, value); 
}

void createMap(Thread t, T firstValue) {
    //threadLocals屬性即為此map
    t.threadLocals = new ThreadLocalMap(this, firstValue);
}

public T get() {
    //拿到當(dāng)前線程
    Thread t = Thread.currentThread();
    //拿到當(dāng)前線程對(duì)應(yīng)的map
    ThreadLocalMap map = getMap(t);
    //如果已有map
    if (map != null) {
        //取值操作, 拿到對(duì)應(yīng)的Entry
        ThreadLocalMap.Entry e = map.getEntry(this);
        if (e != null) {
           @SuppressWarnings("unchecked")
           T result = (T)e.value;
           return result;
        }
    }
    //沒有map, 則去創(chuàng)建初始化一個(gè)map
    return setInitialValue();
}

private T setInitialValue() {
    //initialValue()方法返回的value為null
    T value = initialValue();
    //拿到當(dāng)前線程去創(chuàng)建對(duì)應(yīng)的map
    Thread t = Thread.currentThread();
    ThreadLocalMap map = getMap(t);
    if (map != null)
        map.set(this, value);
    else
        createMap(t, value);
    return value;
}

public void remove() {
    ThreadLocalMap m = getMap(Thread.currentThread());
    if (m != null)
       m.remove(this);
}