实现一个容器，提供两个方法，add,size。写两个线程，线程1添加10个元素到容器中，线程2实现监控元素的个数，当个数到5个时，线程2给出提示并结束。

1. 用普通线程方法来实现
2. 用volitile关键字实现
3. 用wait和notify实现
4. 使用latch替代wait notify实现

普通线程

public class Exercise318<T> {
    private List<T> elements = new ArrayList<>();

    private long size = 0;

    public void add(T t) {
            elements.add(t);
            size++;
    }

    public long size() {
        return size;
    }

    public static void main(String[] args) {
        Exercise318 e = new Exercise318();
        Thread thread1 = new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e1) {
                    e1.printStackTrace();
                }
                e.add(1);
                System.out.println(e.size());
            }
        });
        Thread thread2 = new Thread(() -> {
            while (true) {
                if (e.size() >= 5) {
                    System.out.println("线程2结束");
                    break;
                }
            }
        });
        thread2.start();
        thread1.start();
    }
}

wait notify

private List<T> elements = new ArrayList<>();

    private long size = 0;

    private static Object lock = new Object();

    public void add(T t) {
        elements.add(t);
        size++;
    }

    public long size() {
        return size;
    }

    public static void main(String[] args) {
        Exercise318 e = new Exercise318();
        Thread thread1 = new Thread(() -> {
            synchronized (lock) {
                for (int i = 0; i < 10; i++) {
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e1) {
                        e1.printStackTrace();
                    }
                    if (e.size() == 5) {
                        lock.notify();
                        try {
                            lock.wait();
                        } catch (InterruptedException e1) {
                            e1.printStackTrace();
                        }
                    }

                    e.add(1);
                    System.out.println(e.size());
                }
            }

        });
        Thread thread2 = new Thread(() -> {
            synchronized (lock) {
                if (e.size() != 5) {
                    try {
                        lock.wait();
                    } catch (InterruptedException e1) {
                        e1.printStackTrace();
                    }
                    System.out.println("线程2结束");
                }
                lock.notify();

            }

        });
        thread2.start();
        thread1.start();
    }
}