copyonwriteArrayList of lock lock

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();
        }

In which the volatile keyword: 
ensure consistency of system memory

For example: a plurality of CPU, the CPU 1 performs the update + 1 operation, the number of memory will pull cpu2 be modified when making changes to ensure successful memory update + 1 when modified