Java 8 使用stream.sorted()方法对List进行排序

下面将使用几个例子像你演示如何使用stream.sorted()方法对List进行排序。

1. 对字符串进行排序

1.1 配合Comparator.naturalOrder()方法对List进行排序(在本例中就是按字母序，升序排列)。

package com.mkyong.sorted;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class StreamApplication {

    public static void main(String[] args) {

        List<String> list = Arrays.asList("9", "A", "Z", "1", "B", "Y", "4", "a", "c");

        /* 
        List<String> sortedList = list.stream()
            .sorted(Comparator.naturalOrder())
            .collect(Collectors.toList());

        List<String> sortedList = list.stream()
            .sorted((o1,o2)-> o1.compareTo(o2))
            .collect(Collectors.toList());
        */

        // 使用String的默认比较方法，也就是按字母序进行排序
        List<String> sortedList = list.stream().sorted().collect(Collectors.toList());

        sortedList.forEach(System.out::println);

    }
}

输出

1
4
9
A
B
Y
Z
a
c

1.2 配合Comparator.reverseOrder()方法对List进行排序(即按字母序，降序排列)。

package com.mkyong.sorted;

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class StreamApplication {

    public static void main(String[] args) {

        List<String> list = Arrays.asList("9", "A", "Z", "1", "B", "Y", "4", "a", "c");

        /*
        List<String> sortedList = list.stream()
            .sorted((o1,o2)-> o2.compareTo(o1))
            .collect(Collectors.toList());
        */

        List<String> sortedList = list.stream()
            .sorted(Comparator.reverseOrder())
            .collect(Collectors.toList());

        sortedList.forEach(System.out::println);

    }
}

输出

c
a
Z
Y
B
A
9
4
1

2. 对对象进行排序

2.1 按照年龄升序排列。

package com.mkyong.sorted;

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class StreamApplication {

    static List<User> users = Arrays.asList(
            new User("C", 30),
            new User("D", 40),
            new User("A", 10),
            new User("B", 20),
            new User("E", 50));

    public static void main(String[] args) {

        /*List<User> sortedList = users.stream()
            .sorted((o1, o2) -> o1.getAge() - o2.getAge())
            .collect(Collectors.toList());*/

        List<User> sortedList = users.stream()
            .sorted(Comparator.comparingInt(User::getAge))
            .collect(Collectors.toList());

        sortedList.forEach(System.out::println);

    }

    static class User {

        private String name;
        private int age;

        public User(String name, int age) {
            this.name = name;
            this.age = age;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public int getAge() {
            return age;
        }

        public void setAge(int age) {
            this.age = age;
        }

        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }
}

输出

User{name='A', age=10}
User{name='B', age=20}
User{name='C', age=30}
User{name='D', age=40}
User{name='E', age=50}

2.2 逆序排列

    List<User> sortedList = users.stream()
        .sorted(Comparator.comparingInt(User::getAge)
        .reversed())
        .collect(Collectors.toList());

    sortedList.forEach(System.out::println);

输出

User{name='E', age=50}
User{name='D', age=40}
User{name='C', age=30}
User{name='B', age=20}
User{name='A', age=10}

2.3 根据名字升序排列

    /*List<User> sortedList = users.stream()
        .sorted((o1, o2) -> o1.getName().compareTo(o2.getName()))
        .collect(Collectors.toList());*/

    List<User> sortedList = users.stream()
        .sorted(Comparator.comparing(User::getName))
        .collect(Collectors.toList());