修改CopyOnWrite部分的表述
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@ -255,17 +255,18 @@ List<String> synList = Collections.synchronizedList(list);
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List<String> list = new CopyOnWriteArrayList<>();
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```
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扩展:CopyOnWriteArrayList是一种CopyOnWrite容器,即写时复制的容器。从以下源码中看出:当向容器中添加元素时,不是直接往当前容器添加,而是Copy当前容器,在新容器中添加,添加完后,将原容器的引用指向新容器。这样做可以对CopyOnWrite容器进行并发的读,不需要加锁,极大地提高了读性能,因此适用于读多写少的场景。
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扩展
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CopyOnWriteArrayList是一种CopyOnWrite容器,从以下源码看出:添加元素是在复制的新数组上进行的,然后将原数组的引用指向新数组;读取元素是从原数组读取。这样可以进行并发的且不需加锁的读取,读取效率高,适用于读操作远大于写操作的场景中。
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```java
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public boolean add(E e) {
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final ReentrantLock lock = this.lock;
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final ReentrantLock lock = this.lock;
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lock.lock();
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try {
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Object[] elements = getArray();
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int len = elements.length;
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Object[] newElements = Arrays.copyOf(elements, len + 1); // 复制到新容器
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newElements[len] = e;
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Object[] newElements = Arrays.copyOf(elements, len + 1);
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newElements[len] = e;
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setArray(newElements);
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return true;
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} finally {
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@ -273,9 +274,13 @@ public boolean add(E e) {
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}
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}
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final void setArray(Object[] a) {
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array = a;
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}
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@SuppressWarnings("unchecked")
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private E get(Object[] a, int index) {
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return (E) a[index];
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return (E) a[index];
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}
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```
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