Java retainAll 联想到iOS的交集

ArrayList<String> listA= new ArrayList<String>();
listA.add("Tom");

ArrayList<String> listB= new ArrayList<String>();
listB.add("Brain");
listB.add("Tom");

listA.retainAll(listB);
System.out.println(listA);

NSArray *array1 = @[@"1",@"2",@"3"];
NSArray *array2 = @[@"1",@"5",@"6"];

NSMutableSet *set1 = [NSMutableSet setWithArray:array1];
NSMutableSet *set2 = [NSMutableSet setWithArray:array2];

[set1 unionSet:set2];       //取并集后 set1中为1，2，3，5，6
[set1 intersectSet:set2];  //取交集后 set1中为1
[set1 minusSet:set2];      //取差集后 set1中为2，3