Java CopyOnWriteArrayList源码超详细分析

public class copyOnwriteArrayList<E>
implements List<E>,RandomAccess，Cloneable，java.io.Serializable {
//加锁: ReentrantLock
final transient ReentrantLock lock = new ReentrantLock( ) ;
// volatile:保证可见性
private transient volatile object[ ] array;
//获取数组
final object[] getArray() ireturn array ;
}
//存入数组
final void setArray(object[ ] a) iarray = a;
}
//无参构造方法:初始化数组，容量为日public CopyOnwriteArrayList( ) i
setArray( new object[e]);
}
//有参构造方法:传入集合
public CopyOnwriteArrayList(collection< ? extends E> c) {
object[] elements;
//判断传入的集合是否是CopyOnwriteArrayList类型if (c.getclass() == copyonwriteArrayList.class)
//获取数组
elements = ((copyOnwriteArrayList<?>)c).getArray();else i
//将集合转为数组
elements = c.toArray();
// c.toArray might (incorrectly) not return object[] (see 6260652)1/判断数组是否是object[]
if (elements.getclass() i= object[].class)
//复制数组
elements = Arrays.copyof(elements，elements.length，object[ ].c1
}
setArray(elements) ;
}
setArray(elements ) ;
}

public boolean add(E e) {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
		Object[] elements = getArray();
		int len = elements.length;
		// 拷贝一个长度+1的数组，将元素放到末尾
		Object[] newElements = Arrays.copyOf(elements, len + 1);
        // 填充要追加的元素e
		newElements[len] = e;
        // 覆盖旧数组
		setArray(newElements);
		return true;
	} finally {
		lock.unlock();
	}
}

public E set(int index, E element) {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
		Object[] elements = getArray();
		// 先获取旧元素
		E oldValue = get(elements, index);
		if (oldValue != element) {
			int len = elements.length;
			// 拷贝一个一样的数组，替换下标元素，并写入array
			Object[] newElements = Arrays.copyOf(elements, len);
			newElements[index] = element;
			setArray(newElements);
		} else {
			// 即使元素没有变化，也要写入array，确保volatile的写语义
			// Not quite a no-op; ensures volatile write semantics
			setArray(elements);
		}
		return oldValue;
	} finally {
		lock.unlock();
	}
}

public E remove(int index) {
	final ReentrantLock lock = this.lock;
	lock.lock();
	try {
		Object[] elements = getArray();
		int len = elements.length;
		// 要移除的旧元素
		E oldValue = get(elements, index);
		int numMoved = len - index - 1;
		if (numMoved == 0)
			// 删除的是最后一个元素，直接拷贝一个长度-1的数组写回array即可
			setArray(Arrays.copyOf(elements, len - 1));
		else {
			// 删除的是中间元素，拷贝一个长度-1的数组
			Object[] newElements = new Object[len - 1];
			// 拷贝前半段元素
			System.arraycopy(elements, 0, newElements, 0, index);
			// 拷贝后半段元素
			System.arraycopy(elements, index + 1, newElements, index,
					numMoved);
			// 写回array
			setArray(newElements);
		}
		return oldValue;
	} finally {
		lock.unlock();
	}
}

public E get(int index) {
    // getArray()获取的就是array
    return get(getArray(), index);
}
private E get(Object[] a, int index) {
    return (E) a[index];
}

public int size() {
    return getArray().length;
}