标签：没有 throws checked unlock swa color 替换 源码解析 nbsp
public class CopyOnWriteArrayList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
直译过来，就是写时复制的动态数组。
add(E e)方法，使用可重入锁ReentrantLock，来保证线程安全。通过方法copy一份新的数组数据，新数组长度加1，在末端把新数据放入新数组里面，最后用新数组替代原有数组。使用可重入锁时，注意把解锁操作放在finally里面，保证解锁操作一定会被执行，避免执行过程产生异常导致锁无法释放。
/** * Appends the specified element to the end of this list. * * @param e element to be appended to this list * @return {@code true} (as specified by {@link Collection#add}) */ 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(); } }
add(int index, E e)方法，
同理，操作数组之前，先加锁。
然后检查索引是否越界。
最后，把原数组分成两次copy到新的长度加1的数组上，以索引index为分界线，copy时在index处预留一个空位置，然后在索引位置放入新的数据，这样新数组构造完成，替换原来的数组，释放锁，结束。
/** * Inserts the specified element at the specified position in this * list. Shifts the element currently at that position (if any) and * any subsequent elements to the right (adds one to their indices). * * @throws IndexOutOfBoundsException {@inheritDoc} */ public void add(int index, E element) { final ReentrantLock lock = this.lock; lock.lock(); try { Object[] elements = getArray(); int len = elements.length; if (index > len || index < 0) throw new IndexOutOfBoundsException("Index: "+index+ ", Size: "+len); Object[] newElements; int numMoved = len - index; if (numMoved == 0) newElements = Arrays.copyOf(elements, len + 1); else { newElements = new Object[len + 1]; System.arraycopy(elements, 0, newElements, 0, index); System.arraycopy(elements, index, newElements, index + 1, numMoved); } newElements[index] = element; setArray(newElements); } finally { lock.unlock(); } }
get(int index )方法，简单的通过索引，直接定位数组元素。注意这里索引时，并没有索引是否越界的检查，跟ArrayList不太一样。
/** * {@inheritDoc} * * @throws IndexOutOfBoundsException {@inheritDoc} */ public E get(int index) { return get(getArray(), index); } @SuppressWarnings("unchecked") private E get(Object[] a, int index) { return (E) a[index]; } /** * Gets the array. Non-private so as to also be accessible * from CopyOnWriteArraySet class. */ final Object[] getArray() { return array; }
remove(int index)方法，这个方法的实现跟上面提到的add(int index) 基本一样。只不过在这里，复制数组时，会把index位置的数据直接放弃。
/** * Removes the element at the specified position in this list. * Shifts any subsequent elements to the left (subtracts one from their * indices). Returns the element that was removed from the list. * * @throws IndexOutOfBoundsException {@inheritDoc} */ 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(); } }
CopyOnWriteArrayList add get remove 源码解析
标签：没有 throws checked unlock swa color 替换 源码解析 nbsp
原文地址：https://www.cnblogs.com/zhangxuezhi/p/11872860.html
