实体类
public class User {
Integer id;
Integer age;
String name;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "User [id=" + id + ", age=" + age + ", name=" + name + "]";
}
public User() {
super();
// TODO Auto-generated constructor stub
}
public User(Integer id, Integer age, String name) {
super();
this.id = id;
this.age = age;
this.name = name;
}
}
排序
public static void main(String[] args) {
List<User> list = new ArrayList<User>();
User user = new User(1,15,"小明1");
User user1 = new User(1,16,"小明2");
User user2 = new User(2,17,"小明3");
User user3 = new User(2,18,"小明4");
User user4 = new User(3,19,"小明5");
list.add(user);
list.add(user1);
list.add(user2);
list.add(user3);
list.add(user4);
List<User> sorted = list.stream().sorted(Comparator.comparing(User::getAge)).collect(Collectors.toList());
for (User us : sorted) {
System.out.println(us);
}
}
结果
User [id=1, age=15, name=小明1]
User [id=1, age=16, name=小明2]
User [id=2, age=17, name=小明3]
User [id=2, age=18, name=小明4]
User [id=3, age=19, name=小明5]
聚合
public static void main(String[] args) {
List<User> list = new ArrayList<User>();
User user = new User(1,15,"小明1");
User user1 = new User(1,16,"小明2");
User user2 = new User(2,17,"小明3");
User user3 = new User(2,18,"小明4");
User user4 = new User(3,19,"小明5");
list.add(user);
list.add(user1);
list.add(user2);
list.add(user3);
list.add(user4);
// List<User> sorted = list.stream().sorted(Comparator.comparing(User::getAge)).collect(Collectors.toList());
// for (User us : sorted) {
// System.out.println(us);
// }
Map<Integer, List<User>> collect = list.stream().collect(Collectors.groupingBy(User::getId));
Set<Integer> keySet = collect.keySet();
Iterator<Integer> iterator = keySet.iterator();
while (iterator.hasNext()) {
Integer next = iterator.next();
List<User> list2 = collect.get(next);
System.out.println("---------" + next + "---------");
for (User uu : list2) {
System.out.println(uu);
}
}
}
结果
---------1---------
User [id=1, age=15, name=小明1]
User [id=1, age=16, name=小明2]
---------2---------
User [id=2, age=17, name=小明3]
User [id=2, age=18, name=小明4]
---------3---------
User [id=3, age=19, name=小明5]
最大值最小值
public static void main(String[] args) {
List<User> list = new ArrayList<User>();
User user = new User(1,15,"小明1");
User user1 = new User(1,16,"小明2");
User user2 = new User(2,17,"小明3");
User user3 = new User(2,18,"小明4");
User user4 = new User(3,19,"小明5");
list.add(user);
list.add(user1);
list.add(user2);
list.add(user3);
list.add(user4);
Optional<User> max = list.stream()
.collect(
Collectors.maxBy(Comparator.comparing(User::getAge))
);
Optional<User> min = list.stream()
.collect(
Collectors.minBy(Comparator.comparing(User::getAge))
);
System.out.println("max--> " + max+" min--> "+ min);
}
结果
max--> Optional[User [id=3, age=19, name=小明5]] min--> Optional[User [id=1, age=15, name=小明1]]
