Java 8 Stream List

Source

Student xm = new Student();
xm.setId(11);
xm.setName("小明");
xm.setGender(1);

Student xh = new Student();
xh.setId(12);
xh.setName("小红");
xh.setGender(2);

Student xt = new Student();
xt.setId(13);
xt.setName("小天");
xt.setGender(1);

List<Student> list = new ArrayList<>();
list.add(xm);
list.add(xh);
list.add(xt);

x01

Operate:

List<Integer> ids = list.stream().map(Student::getId).collect(Collectors.toList());

Result:

[11, 12, 13]

x02

Operate:

Map<Integer, String> idNames = list.stream().collect(Collectors.toMap(Student::getId, Student::getName));

Result:

{11: "小明", 12: "小红", 13: "小天"}

x03

Operate:

Map<Integer, Student> idMap = list.stream().collect(Collectors.toMap(Student::getId, Function.identity()));

Result:

{
  11: {"id": 11, "name": "小明", "gender": 1},
  12: {"id": 12, "name": "小红", "gender": 2},
  13: {"id": 13, "name": "小天", "gender": 1}
}

x04

Operate:

Map<Integer, List<Student>> genderListMap = list.stream().collect(Collectors.groupingBy(Student::getGender));

Result:

{
  1: [{"id": 11, "name": "小明", "gender": 1}, {"id": 13, "name": "小天", "gender": 1}],
  2: [{"id": 12, "name": "小红", "gender": 2}]
}

x05

Operate:

Map<Integer, List<String>> genderListNameMap = list.stream().collect(Collectors.groupingBy(Student::getId, Collectors.mapping(Student::getName, Collectors.toList())));

Result:

{
  1: ["小明", "小天"],
  2: ["小红"]
}

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