public class OuterClass {
    public static String OUTER_DATE = "外部類靜態(tài)變量加載時(shí)間 "+System.currentTimeMillis();
    static {
        System.out.println("外部類靜態(tài)塊加載時(shí)間：" + System.currentTimeMillis());
    }
    public OuterClass() {
        System.out.println("外部類構(gòu)造函數(shù)時(shí)間：" + System.currentTimeMillis());
    }
    static class InnerStaticClass{
        public static String INNER_STATIC_DATE = "靜態(tài)內(nèi)部類靜態(tài)變量加載時(shí)間 "+System.currentTimeMillis();
        private String name;
        static {
            System.out.println("靜態(tài)內(nèi)部類靜態(tài)代碼塊加載時(shí)間：" + System.currentTimeMillis());
        }
    }
    class InnerClass {
        public String INNER_DATE = "";
        public InnerClass() {
            INNER_DATE = "非靜態(tài)內(nèi)部類構(gòu)造器加載時(shí)間"+System.currentTimeMillis();
        }
    }
    public static void main(String[] args) {
        OuterClass outer = new OuterClass();
        System.out.println("非靜態(tài)內(nèi)部類加載時(shí)間: "+outer.new InnerClass().INNER_DATE);
        /**
         * 內(nèi)部靜態(tài)類可以直接用，不需要new
         * 靜態(tài)內(nèi)部類的加載是代碼中需要靜態(tài)內(nèi)部類的時(shí)候才加載，而不是和外部類一起加載的
         * 加載靜態(tài)內(nèi)部類之前，先把外部類的靜態(tài)變量和靜態(tài)代碼塊先執(zhí)行完
         * 執(zhí)行完外部類的代碼后，再執(zhí)行靜態(tài)內(nèi)部類的 靜態(tài)變量和靜態(tài)代碼塊
         * 靜態(tài)內(nèi)部類的 靜態(tài)變量和靜態(tài)代碼塊執(zhí)行完后，然后執(zhí)行業(yè)務(wù)代碼
         * new  外部類的時(shí)候 。外部類的靜態(tài)代碼塊和靜態(tài)變量先執(zhí)行，外部類構(gòu)造函數(shù)后執(zhí)行
         */
        System.out.println("靜態(tài)內(nèi)部類加載時(shí)間____："+InnerStaticClass.INNER_STATIC_DATE);
    }
}
//什么時(shí)候考慮使用靜態(tài)內(nèi)部類?
//A類中需要一個(gè)B類，但是B類只為A類服務(wù)，這種情況不需要將B類單獨(dú)剝離，只需要在A內(nèi)部即可
//一個(gè)類的構(gòu)建有非常多參數(shù)或者十分復(fù)雜的一個(gè)對(duì)象的時(shí)候--引申到了建造者模式

public class ThreadLocaDemo {
    private static ThreadLocal<String> localVar = new ThreadLocal<String>();
    static void print(String str) {
        //打印當(dāng)前線程中本地內(nèi)存中本地變量的值
        System.out.println(str + " :" + localVar.get());
        //清除本地內(nèi)存中的本地變量
        localVar.remove();
    }
    public static void main(String[] args) throws InterruptedException {
        new Thread(new Runnable() {
            public void run() {
                ThreadLocaDemo.localVar.set("local_A");
                print("A");
                //打印本地變量
                System.out.println("after remove : " + localVar.get());
            }
        },"A").start();
        Thread.sleep(1000);
        new Thread(new Runnable() {
            public void run() {
                ThreadLocaDemo.localVar.set("local_B");
                print("B");
                System.out.println("after remove : " + localVar.get());
            }
        },"B").start();
    }
}

 public void set(T value) {
        //1、獲取當(dāng)前線程
        Thread t = Thread.currentThread();
        //2、獲取線程中的屬性 threadLocalMap ,如果threadLocalMap 不為空，
        //則直接更新要保存的變量值，否則創(chuàng)建threadLocalMap，并賦值
        ThreadLocalMap map = getMap(t);
        if (map != null)
            map.set(this, value);
        else
            // 初始化thradLocalMap 并賦值
            createMap(t, value);
    }

  static class ThreadLocalMap {
        /**
         * The entries in this hash map extend WeakReference, using
         * its main ref field as the key (which is always a
         * ThreadLocal object).  Note that null keys (i.e. entry.get()
         * == null) mean that the key is no longer referenced, so the
         * entry can be expunged from table.  Such entries are referred to
         * as "stale entries" in the code that follows.
         */
        static class Entry extends WeakReference<ThreadLocal<?>> {
            /** The value associated with this ThreadLocal. */
            Object value;
            Entry(ThreadLocal<?> k, Object v) {
                super(k);
                value = v;
            }
        }
    }

//這個(gè)是threadlocal 的內(nèi)部方法
void createMap(Thread t, T firstValue) {
        t.threadLocals = new ThreadLocalMap(this, firstValue);
    }
    //ThreadLocalMap 構(gòu)造方法
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);
        }

    public T get() {
        //1、獲取當(dāng)前線程
        Thread t = Thread.currentThread();
        //2、獲取當(dāng)前線程的ThreadLocalMap
        ThreadLocalMap map = getMap(t);
        //3、如果map數(shù)據(jù)為空，
        if (map != null) {
            //3.1、獲取threalLocalMap中存儲(chǔ)的值
            ThreadLocalMap.Entry e = map.getEntry(this);
            if (e != null) {
                @SuppressWarnings("unchecked")
                T result = (T)e.value;
                return result;
            }
        }
        //如果是數(shù)據(jù)為null，則初始化，初始化的結(jié)果，TheralLocalMap中存放key值為threadLocal，值為null
        return setInitialValue();
    }
private T setInitialValue() {
        T value = initialValue();
        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);
     }