CopyOnWriteArrayList是jdk1.5并法包里面用于处理高并发下。读多写少的情况下。减少锁等待的集合类。以下对该类实现做一个简要的分析

1，首先CopyOnWriteArrayList是实现了List接口，对=List接口的相关方法进行了实现。

2，以下的它的add方法，会首先加锁，然后copy原List内部的数组，然后对新数组长度加1后释放锁。因为数组copy速度非常快，切在读多写少的情况下锁开销比較少

    public boolean add(E e) {

        final ReentrantLock lock = this.lock;

        lock.lock();

        try {

            Object[] elements = getArray();

            int len = elements.length;

            Object[] newElements = Arrays.copyOf(elements, len + 1);

            newElements[len] = e;

            setArray(newElements);

            return true;

        } finally {

            lock.unlock();

        }

    }

2，它的迭代器COWIterator不是高速失败的。以下是它的源代码

private COWIterator(Object[] elements, int initialCursor) {

            cursor = initialCursor;

            snapshot = elements;

        }

        public boolean hasNext() {

            return cursor < snapshot.length;

        }

        public boolean hasPrevious() {

            return cursor > 0;

        }

        @SuppressWarnings("unchecked")

        public E next() {

            if (! hasNext())

                throw new NoSuchElementException();

            return (E) snapshot[cursor++];

        }

3，以下是它的remove方法，加锁原理同add方法

    public E remove(int index) {

        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)

                setArray(Arrays.copyOf(elements, len - 1));

            else {

                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 {

            lock.unlock();

        }

    }