Java8 Stream详解~排序：sorted

sorted，中间操作。有两种排序：

• sorted()：自然排序，流中元素需实现Comparable接口

• sorted(Comparator com)：Comparator排序器自定义排序

「案例：将员工按工资由高到低（工资一样则按年龄由大到小）排序」

public class StreamTest {
 public static void main(String[] args) {
  List personList = new ArrayList();

  personList.add(new Person("Sherry", 9000, 24, "female", "New York"));
  personList.add(new Person("Tom", 8900, 22, "male", "Washington"));
  personList.add(new Person("Jack", 9000, 25, "male", "Washington"));
  personList.add(new Person("Lily", 8800, 26, "male", "New York"));
  personList.add(new Person("Alisa", 9000, 26, "female", "New York"));

  // 按工资升序排序（自然排序）
  List newList = personList.stream().sorted(Comparator.comparing(Person::getSalary)).map(Person::getName)
    .collect(Collectors.toList());
  // 按工资倒序排序
  List newList2 = personList.stream().sorted(Comparator.comparing(Person::getSalary).reversed())
    .map(Person::getName).collect(Collectors.toList());
  // 先按工资再按年龄升序排序
  List newList3 = personList.stream()
    .sorted(Comparator.comparing(Person::getSalary).thenComparing(Person::getAge)).map(Person::getName)
    .collect(Collectors.toList());
  // 先按工资再按年龄自定义排序（降序）
  List newList4 = personList.stream().sorted((p1, p2) -> {
   if (p1.getSalary() == p2.getSalary()) {
    return p2.getAge() - p1.getAge();
   } else {
    return p2.getSalary() - p1.getSalary();
   }
  }).map(Person::getName).collect(Collectors.toList());

  System.out.println("按工资升序排序：" + newList);
  System.out.println("按工资降序排序：" + newList2);
  System.out.println("先按工资再按年龄升序排序：" + newList3);
  System.out.println("先按工资再按年龄自定义降序排序：" + newList4);
 }
}