Merge pull request #321 from xiangflight/master

CopyOnWriteArrayList简介

.gitignore

@@ -0,0 +1 @@
+.DS_Store

notes/Java 容器.md

@@ -255,6 +255,35 @@ List<String> synList = Collections.synchronizedList(list);
 List<String> list = new CopyOnWriteArrayList<>();
 ```
 
+CopyOnWriteArrayList是一种CopyOnWrite容器，从以下源码看出：读取元素是从原数组读取；添加元素是在复制的新数组上。读写分离，因而可以在并发条件下进行不加锁的读取，读取效率高，适用于读操作远大于写操作的场景。
+
+```java
+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();
+    }
+}
+
+final void setArray(Object[] a) {
+    array = a;
+}
+
+@SuppressWarnings("unchecked")
+private E get(Object[] a, int index) {
+    return (E) a[index]; 
+}
+
+```
+
 ## LinkedList
 
 ### 1. 概览