Java List集合交集并集

数组转集合

List<String> list=Arrays.asList("1","2");

注意转换出来的List为Arrays内部类集合，与常规的ArrayList有区别，比如常见的remove(e)等方法不可用。

如何转换为常规数组

List<String> list=new ArrayList<>(Arrays.asList("1","2"))

两个集合交集

交集说明：只取两个数组都存在的元素

DEMO 1

List<String> listA = new ArrayList<>(Arrays.asList("1","2","3"));
List<String> listB = new ArrayList<>(Arrays.asList("2","3","5"));
​
​
boolean isChanged=listB.retainAll(listA);
System.out.println(isChanged);
System.out.println(Arrays.toString(listB.toArray()))
​

输出结果：

["2","3"]

DEMO 2

List<String> listA = new ArrayList<>(Arrays.asList("1","2","3"));
List<String> listC = new ArrayList<>(Arrays.asList("5","6"));
listC.retainAll(listA);
System.out.println(Arrays.toString(listC.toArray()))

输出结果：

[]

两个集合并集

并集说明：两个集合合并成一个（可以存在相同元素）

DEMO 1

List<String> listA = new ArrayList<>(Arrays.asList("1","2","3"));
List<String> listB = new ArrayList<>(Arrays.asList("2","3","5"));
​
listB.addAll(listA);
System.out.println(Arrays.toString(listB.toArray()))
​

输出结果：

["1","2","3","2","3","5"]

DEMO 2

List<String> listA = new ArrayList<>(Arrays.asList("1","2","3"));
List<String> listC = new ArrayList<>(Arrays.asList("5","6"));
​
listC.addAll(listA);
System.out.println(Arrays.toString(listC.toArray()))
​

输出结果：

["1","2","3","5","6"]

两个集合并集去重

两个集合合并，且删除重复元素

DEMO 1

List<String> listA = new ArrayList<>(Arrays.asList("1","2","3"));
List<String> listB = new ArrayList<>(Arrays.asList("2","3","5"));
​
listB.removeAll(listA);
listB.addAll(listA);
System.out.println(Arrays.toString(listB.toArray()))

输出结果：

["1","2","3","5"]

两个集合差集

集合差集说明：A集合删除B集合里面与A相同的元素,保留A集合有B集合没有的部分

DEMO 1

List<String> listA = new ArrayList<>(Arrays.asList("1","2","3"));
List<String> listB = new ArrayList<>(Arrays.asList("2","3","5"));
​
listB.removeAll(listA);
System.out.println(Arrays.toString(listB.toArray()))

输出结果：

["5"]

DEMO 2

List<String> listA = new ArrayList<>(Arrays.asList("1","2","3"));
List<String> listC = new ArrayList<>(Arrays.asList("5","6"));
​
listC.removeAll(listA);
System.out.println(Arrays.toString(listC.toArray()))
​

输出结果：

["5","6"]