A Guide to ArrayList

素颜马尾好姑娘i 2024-03-22 22:04 63阅读 0赞

### 特点 ###

*  存储的元素有序可重复
 *  ArrayList built atop an array, which is able to dynamically grow and shrink as you add/remove elements.

### This ArrayListhas the following properties: ###

*  Random access takes O(1) time（支持高效的随机元素访问）
 *  Adding element takes amortized constant time O(1)
 *  Inserting/Deleting takes O(n) time
 *  Searching takes O(n) time for unsorted array and O(log n) for a sorted one

**[时间复杂度函数图像][Link 1]**

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List<String> list = Arrays.asList("a", "b", "c");
    List<String> list = new ArrayList(Arrays.asList("a", "b", "c"));

list.add("e");
    list.add(1,"c");
    list.addAll(list2);
    list.addAll(1, list2);
    
    list.clear();
    list.remove(0);                   // 删除对应索引的元素
    list.remove("a")                  // 删除指定元素、从前往后删除
    list.removeAll(list2)             // 删除所有元素
    list.removeIf(a->a.equals("a"))   // 有条件的删除
    
    list.set(1, "e")
    list.replaceAll(a -> a + "@");   // 对所有元素进行一次加工
    
    list.contains("a")               // 判断是否包含、包含返回true
    list.isEmpty()
    list.size()
    list.get(0)
    list.indexOf("a")                // 判断元素第一次出现的索引,不存在则返回-1
    list.lastIndexOf("b")            // 获取元素最后一次出现的索引
    list.retainAll(list2);           // 取交集
    
    
    list.sort(Comparator.comparing(a->a.length()));
    List<String> strings = list.subList(1, 2); // 获取子列表
    String[] arr = list.toArray(new String[0]);

--------------------

<dependency>
        <groupId>org.apache.commons</groupId>
        <artifactId>commons-collections4</artifactId>
        <version>4.4</version>
    </dependency>
    
    CollectionUtils.isEmpty(list);
    CollectionUtils.isNotEmpty(list)
    
    CollectionUtils.retainAll(collA, collB);                  // 交集
    CollectionUtils.union(collA, collB);                      // 并集
    CollectionUtils.subtract(collA, collB);                   // 差集
    CollectionUtils.disjunction(listA,listB);                 // 交集的补集
    
    CollectionUtils.unmodifiableCollection(Collection collection)  // 不可修改的集合 
    CollectionUtils.isEqualCollection(collA, collB);          // 判等

--------------------

参考：  
**[ArrayList最常用的方法总结][ArrayList]**  
**[CollectionUtils有哪些666的方法][CollectionUtils_666]**

[Link 1]: https://blog.csdn.net/weixin_37646636/article/details/131978054
[ArrayList]: https://juejin.cn/post/7103563495773306887
[CollectionUtils_666]: https://juejin.cn/post/7106138716049473566