Java ThreadLocal

class X {        public static ThreadLocal threadLocal = new ThreadLocal();    ...    threadLocal.set("thread local value");    ...}
class Y {    ...    String value = (String)X.treadLocal.get();    ...}

...
public void set(T value) {    Thread t = Thread.currentThread();    ThreadLocalMap map = getMap(t);    if (map != null) {        map.set(this, value); // this 指向 ThreadLocal 在堆中的实例对象    } else {        creatMap(t, value);    }}
...
void createMap(Thread t, T firstValue) {    // 每个线程都会有各自的 map    t.threadLocals = new ThreadLocalMap(this, firstValue);}
ThreadLocalMap getMap(Thread t) {    return t.threadLocals;}