The underlying principle of CopyOnWriteArrayList in java - Interview Guide

CopyOnWriteArrayList is a thread-safe list implementation class in Java. Its underlying principle is that every time a modification operation is performed (such as adding or deleting elements), a new array will be created to replace the old array. Specifically, CopyOnWriteArrayList maintains an array internally (called a copy array) and maintains a mutable variable to record the current array version. When the list needs to be modified, CopyOnWriteArrayList will create a new array copy and perform the modification operation. After the modification is completed, the new array copy will replace the old array copy and the version variable will be updated. Since each modification creates a new copy, the original read operation is not affected and can continue. The advantage of this implementation is that the read operation does not require locking, because the read operation does not modify the array contents. Moreover, the performance is better in scenarios where there is more reading and less writing. However, the disadvantage is that multiple modification operations are mutually exclusive, that is, only one modification operation can be performed at the same time, because each modification requires the creation of a new array copy, which takes up more memory space. It should be noted that CopyOnWriteArrayList is suitable for scenarios where there is more reading and less writing. If writing operations are very frequent, creating a new array copy each time will bring significant overhead. At this time, you may need to consider other thread-safe list implementation classes. .

​The following is a simple sample code showing the use of CopyOnWriteArrayList:

javaCopy codeimport java.util.concurrent.CopyOnWriteArrayList;
public class CopyOnWriteArrayListExample {
    public static void main(String[] args) {
        CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
        // 添加元素
        list.add("Apple");
        list.add("Banana");
        list.add("Orange");
        // 打印列表
        System.out.println("List: " + list);
        // 修改元素
        list.set(1, "Grape");
        // 删除元素
        list.remove("Apple");
        // 打印修改后的列表
        System.out.println("Updated list: " + list);
    }
}

The above code creates a CopyOnWriteArrayList object and performs some basic operations, including adding elements, modifying elements, and deleting elements. Changes to the list can be observed by outputting the results. It should be noted that CopyOnWriteArrayList will create a new array copy for each modification operation, so it may occupy more memory space during modification operations.