Java中的CopyOnWriteArrayList容器解析

private transient volatile Object[] array;

public boolean add(E e) {
        //ReentrantLock加锁，保证线程安全
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            Object[] elements = getArray();
            int len = elements.length;
            //拷贝原容器，长度为原容器长度加一
            Object[] newElements = Arrays.copyOf(elements, len + 1);
            //在新副本上执行添加操作
            newElements[len] = e;
            //将原容器引用指向新副本
            setArray(newElements);
            return true;
        } finally {
            //解锁
            lock.unlock();
        }
    }

public E remove(int index) {
        //加锁
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            Object[] elements = getArray();
            int len = elements.length;
            E oldValue = get(elements, index);
            int numMoved = len - index - 1;
            if (numMoved == 0)
                //如果要删除的是列表末端数据，拷贝前len-1个数据到新副本上，再切换引用
                setArray(Arrays.copyOf(elements, len - 1));
            else {
                //否则，将除要删除元素之外的其他元素拷贝到新副本中，并切换引用
                Object[] newElements = new Object[len - 1];
                System.arraycopy(elements, 0, newElements, 0, index);
                System.arraycopy(elements, index + 1, newElements, index,
                                 numMoved);
                setArray(newElements);
            }
            return oldValue;
        } finally {
            //解锁
            lock.unlock();
        }
    }

public E get(int index) {
        return get(getArray(), index);
    }

 	private E get(Object[] a, int index) {
        return (E) a[index];
    }

// 演示多线程下迭代器的弱一致性结果
public class copylist {
    private static volatile CopyOnWriteArrayList<String> arrayList = new CopyOnWriteArrayList<>();
    public static void main(String[] args) throws InterruptedException {
        arrayList.add("hello");
        arrayList.add("alibaba");
        arrayList.add("welcome");
        arrayList.add("to");
        arrayList.add("hangzhou");
        Thread threadOne = new Thread(new Runnable() {
            @Override
            public void run() {
                // 修改list中下标为1的元素为ali
                arrayList.set(1, "ali");
                // 删除元素
                arrayList.remove(2);
                arrayList.remove(3);
            }
        });
        // 保证在修改线程启动前获取迭代器
        Iterator<String> itr = arrayList.iterator();
        // 启动线程
        threadOne.start();
        // 等待子线程执行完毕
        threadOne.join();
        while(itr.hasNext()) {
            System.out.println(itr.next());
        }
    }
}

List list = Collections.synchronizedList(new ArrayList());