Java 中 List 集合取交集

Dear 丶 2024-03-30 10:32 38阅读 0赞

**交集 Intersection 英 \[ˌɪntəˈsekʃn\]**  
**并集 Union 英 \[ˈjuːniən\]**  
**差集 difference of set**  
**补集 complement set 英 \[ˈkɒmplɪment\]**  
**[Java 中 List 集合取交集][Java _ List]**  
**[Java 中 List 集合取并集][Java _ List 1]**  
**[Java 中 List 集合取差集][Java _ List 2]**  
**[Java 中 List 集合取补集][Java _ List 3]**

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### 1、java.util.List\#retainAll ###

# 侵入式取交集，会改变原集合
    List<Integer> list1 = new ArrayList(Arrays.asList(1, 2, 3, 4, 5));
    List<Integer> list2 = new ArrayList(Arrays.asList(1, 2, 3, 6, 7, 8, 9));
    list1.retainAll(list2);
    
    list1 取交集前:[1, 2, 3, 4, 5]
    list2 取交集前:[1, 2, 3, 6, 7, 8, 9]
    list1 取交集后:[1, 2, 3]
    list2 取交集后:[1, 2, 3, 6, 7, 8, 9]

# 规避侵入式取交集
    List<Integer> list1 = new ArrayList(Arrays.asList(1, 2, 3, 4, 5));
    List<Integer> list2 = new ArrayList(Arrays.asList(1, 2, 3, 6, 7, 8, 9));
    List<Integer> list3 = new ArrayList(list1);
    list3.retainAll(list2);
    
    list1 取交集前:[1, 2, 3, 4, 5]
    list2 取交集前:[1, 2, 3, 6, 7, 8, 9]
    list3 取交集前:[1, 2, 3, 4, 5]
    list1 取交集后:[1, 2, 3, 4, 5]
    list2 取交集后:[1, 2, 3, 6, 7, 8, 9]
    list3 取交集后:[1, 2, 3]

# 判断是否有交集
    List<Integer> list1 = new ArrayList(Arrays.asList(1, 2, 3, 4, 5));
    List<Integer> list2 = new ArrayList(Arrays.asList(1, 2, 3, 6, 7, 8, 9));
    
    boolean existIntersection2 = new ArrayList(list1).retainAll(list2);
    true
    
    ----------------------------------------------------------------------
    # 这种居然不算有交集→→→→→→→→→→→→→→→→→→→→→这里他妈的有大坑啊
    List<Integer> list1 = new ArrayList(Arrays.asList(1, 2, 3, 6, 7, 8, 9));
    List<Integer> list2 = new ArrayList(Arrays.asList(1, 2, 3, 6, 7, 8, 9));
    boolean existIntersection2 = new ArrayList(list1).retainAll(list2);
    false
    
    List<Integer> list1 = new ArrayList();
    List<Integer> list2 = new ArrayList();
    boolean existIntersection2 = new ArrayList(list1).retainAll(list2);
    false
    
    ----------------------------------------------------------------------
    # 注意规避NullPointerException场景
    List<Integer> list1 = new ArrayList();
    List<Integer> list2 = null;
    boolean existIntersection2 = new ArrayList(list1).retainAll(list2);
    NullPointerException
    
    List<Integer> list1 = null;
    List<Integer> list2 = new ArrayList();
    boolean existIntersection2 = new ArrayList(list1).retainAll(list2);
    NullPointerException

### 2、org.apache.commons.collections.CollectionUtils\#intersection ###

List<Integer> list1 = new ArrayList(Arrays.asList(1, 2, 3, 4, 5));
    List<Integer> list2 = new ArrayList(Arrays.asList(1, 2, 3, 6, 7, 8, 9));
    Collection intersection = CollectionUtils.intersection(list1, list2);
    交集结果是: [1, 2, 3]
    
    List<Integer> list1 = new ArrayList(Arrays.asList(1, 2, 3, 6, 7, 8, 9));
    List<Integer> list2 = new ArrayList(Arrays.asList(1, 2, 3, 6, 7, 8, 9));
    Collection intersection = CollectionUtils.intersection(list1, list2);
    交集结果是: [1, 2, 3, 6, 7, 8, 9]
    
    List<Integer> list1 = new ArrayList();
    List<Integer> list2 = new ArrayList();
    Collection intersection = CollectionUtils.intersection(list1, list2);
    交集结果是: []
    
    List<Integer> list1 = null;
    List<Integer> list2 = new ArrayList();
    Collection intersection = CollectionUtils.intersection(list1, list2);
    NullPointerException
    
    List<Integer> list1 = new ArrayList();
    List<Integer> list2 = null;
    Collection intersection = CollectionUtils.intersection(list1, list2);
    NullPointerException

List<Integer> list1 = new ArrayList(Arrays.asList(1, 2, 3, 4, 5));
    List<Integer> list2 = new ArrayList(Arrays.asList(1, 2, 3, 6, 7, 8, 9));
    boolean existIntersection2 = new ArrayList(list1).retainAll(list2);
    true
    
    ----------------------------------------------------------------------
    # 这种居然不算有交集→→→→→→→→→→→→→→→→→→→→→这里他妈的有大坑啊
    List<Integer> list1 = new ArrayList(Arrays.asList(1, 2, 3, 6, 7, 8, 9));
    List<Integer> list2 = new ArrayList(Arrays.asList(1, 2, 3, 6, 7, 8, 9));
    boolean existIntersection2 = new ArrayList(list1).retainAll(list2);
    false
    
    List<Integer> list1 = new ArrayList();
    List<Integer> list2 = new ArrayList();
    boolean existIntersection2 = new ArrayList(list1).retainAll(list2);
    false
    ----------------------------------------------------------------------

[Java _ List]: https://blog.csdn.net/weixin_37646636/article/details/128378090
[Java _ List 1]: https://blog.csdn.net/weixin_37646636/article/details/128378917
[Java _ List 2]: https://blog.csdn.net/weixin_37646636/article/details/128378928
[Java _ List 3]: https://blog.csdn.net/weixin_37646636/article/details/132713502