Java 中 List 集合取并集

ゝ一世哀愁。 2024-03-30 10:33 67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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# 侵入式取交集，会改变原集合
    List<Integer> list1 = new ArrayList(Arrays.asList(1, 2, 3));
    List<Integer> list2 = new ArrayList(Arrays.asList(3, 6, 7, 8, 9));
    
    list1.addAll(list2);
    
    list1 取并集前:[1, 2, 3]
    list2 取并集前:[3, 6, 7, 8, 9]
    list1 取并集后:[1, 2, 3, 3, 6, 7, 8, 9]
    list2 取并集后:[3, 6, 7, 8, 9]

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

# 并集去重
    List<Integer> list1 = new ArrayList(Arrays.asList(1, 2, 3));
    List<Integer> list2 = new ArrayList(Arrays.asList(3, 6, 7, 8, 9));
    
    HashSet<Integer> set = new HashSet();
    set.addAll(list1);
    set.addAll(list2);
    
    list1 取并集前:[1, 2, 3]
    list2 取并集前:[3, 6, 7, 8, 9]
    list1 取并集后:[1, 2, 3]
    list2 取并集后:[3, 6, 7, 8, 9]
    set   并集去重:[1, 2, 3, 6, 7, 8, 9]

# 并集去重
    List<Integer> list1 = new ArrayList(Arrays.asList(1, 2, 3));
    List<Integer> list2 = new ArrayList(Arrays.asList(3, 6, 7, 8, 9));
    
    Collection union = CollectionUtils.union(list1, list2);
    
    list1 取并集前:[1, 2, 3]
    list2 取并集前:[3, 6, 7, 8, 9]
    list1 取并集后:[1, 2, 3]
    list2 取并集后:[3, 6, 7, 8, 9]
    union 取并集后:[1, 2, 3, 6, 7, 8, 9]

[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