Intersection, Difference, and Union of lists

I used the difference set of lists in my work, and found it to be quite useful.
So record it.

need	list method	illustrate	Remark
intersection	listA.retainAll(listB)	The content of listA becomes an object where both listA and listB exist	listB does not change
difference	listA.removeAll(listB)	Deduplication of the content of listB that exists in listA	listB does not change
union	listA.removeAll(listB) listA.addAll(listB)	In order to remove duplicates, listA first takes the difference, and then appends all listB	listB does not change

Test code:

// 交集
List<String> listA_01 = new ArrayList<String>(){{
    add("A");
    add("B");
}};
List<String> listB_01 = new ArrayList<String>(){{
    add("B");
    add("C");
}};
listA_01.retainAll(listB_01);
System.out.println(listA_01); // 结果:[B]
System.out.println(listB_01); // 结果:[B, C]

// 差集
List<String> listA_02 = new ArrayList<String>(){{
    add("A");
    add("B");
}};
List<String> listB_02 = new ArrayList<String>(){{
    add("B");
    add("C");
}};
listA_02.removeAll(listB_02);
System.out.println(listA_02); // 结果:[A]
System.out.println(listB_02); // 结果:[B, C]

// 并集
List<String> listA_03 = new ArrayList<String>(){{
    add("A");
    add("B");
}};
List<String> listB_03 = new ArrayList<String>(){{
    add("B");
    add("C");
}};
listA_03.removeAll(listB_03);
listA_03.addAll(listB_03);
System.out.println(listA_03); // 结果:[A, B, C]
System.out.println(listB_03); // 结果:[B, C]