• wait() 阻塞秃流，釋放鎖
• notify() 通知阻塞的那個線程到就緒狀態(tài)糖赔，但不是讓出鎖給他刻撒，被喚醒的線程要運行必須得獲得鎖醋火。

示例：

public class NotifyFreeLock {

    //添加volatile，使t2能夠得到通知
    volatile List lists = new ArrayList();

    public void add(Object o) {
        lists.add(o);
    }

    public int size() {
        return lists.size();
    }
    
    public static void main(String[] args) {
        T04_NotifyFreeLock c = new T04_NotifyFreeLock();
        
        final Object lock = new Object();
        
        new Thread(() -> {
            synchronized(lock) {
                System.out.println("t2啟動");
                if(c.size() != 5) {
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println("t2 結(jié)束");
                //通知t1繼續(xù)執(zhí)行
                lock.notify();
            }
            
        }, "t2").start();
        
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }

        new Thread(() -> {
            System.out.println("t1啟動");
            synchronized(lock) {
                for(int i=0; i<10; i++) {
                    c.add(new Object());
                    System.out.println("add " + i);
                    
                    if(c.size() == 5) {
                        lock.notify();
                        //釋放鎖为黎，讓t2得以執(zhí)行
                        try {
                            lock.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    
                    try {
                        TimeUnit.SECONDS.sleep(1);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }, "t1").start();
        
        
    }
}