使用LinkedList实现安全队列

         使用 wait notify 实现一个队列，队列有2个方法，add 和 get 。add方法往队列中添加元素，get方法往队列中获得元素。队列必须是线程安全的。如果get执行时，队列为空，线程必须阻塞等待，直到有队列有数据。如果add时，队列已经满，则add线程要等待，直到队列有空闲空间。 

/**
 * 使用LinkedList实现安全队列
 *
 */
public class SafeLinkedList<E> {


    private LinkedList<E> data = new LinkedList<>();
    private int totalSize;

    public SafeLinkedList(int totalSize) {
        this.totalSize = totalSize;

    }

    /**
     * 当队列已满时候，阻塞，直到取走数据为止
     * @param e
     */
    public void add(E e) {
        synchronized (data) {
            if (data.size() == totalSize) {
                try {
                    data.wait();
                } catch (InterruptedException e1) {
                    Thread.interrupted();
                    data.notifyAll();
                    System.out.println("队列已满啦！");
                }

            }
            data.add(e);
            data.notifyAll();

        }

    }

    /**
     * 当队列为空时候，阻塞等待
     * @return
     */
    public E get() {
        synchronized (data) {

            if (data.isEmpty()) {
                try {
                    data.wait();
                } catch (InterruptedException e) {
                    Thread.interrupted();
                    data.notifyAll();
                }
            }

            E e = data.getFirst();//获取队列头元素
            data.removeFirst();//移除对头元素
            data.notifyAll();
            return e;
        }
    }

    public synchronized int size() {
        return data.size();
    }
}

测试队列：

/**
 * 多线程条件下测试LinkedList存取数据是否安全
 */
public class SafeLinkedListTest {

    private SafeLinkedList<String> data = new SafeLinkedList<>(10);

    @Test
    public void putGetTest() throws InterruptedException {

        //add test
        Thread t1 = new Thread(new OperAddThread());
        Thread t2 = new Thread(new OperAddThread());
        Thread t3 = new Thread(new OperAddThread());

        Thread getThread = new Thread(new OperGetThread());
        getThread.setName("getThread");

        t1.start();
        t2.start();
        t3.start();
        getThread.start();

        t1.join();
        t2.join();
        t3.join();
        getThread.join();

        System.out.println(data.size());

    }


    class OperAddThread implements Runnable {

        @Override
        public void run() {
            for (int i = 0; i < 4; i++) {
                String addData=Thread.currentThread().getName()+"|"+String.valueOf(i);
                data.add(addData);
                System.out.println("add size=" + data.size());
                System.out.println(Thread.currentThread().getName() + " addData=" + addData);
            }
        }
    }

    class OperGetThread implements Runnable {
        @Override
        public void run() {
            int i=11;
            while (i>=0) {
                i--;
                String value = data.get();
                System.out.println("get size=" + data.size());
                System.out.println("get string--" + " ;value=" + value);
            }
        }
    }
}