Few examples to show you how to sort a List with stream.sorted()

1. List

1.1 Sort a List with Comparator.naturalOrder()

package com.favtuts.java8.stream;

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

public class StreamSortList {

    public static void main(String[] args) {
        sortListWithComparatorNaturalOrder();
    }

    static void sortListWithComparatorNaturalOrder() {
        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());
         */

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

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

Output

1
4
9
A
B
Y
Z
a
c

1.2 Sort a List with Comparator.reverseOrder()

package com.favtuts.java8.stream;

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

public class StreamSortList {

    public static void main(String[] args) {
        sortListWithComparatorReverseOrder();
    }

    static void sortListWithComparatorReverseOrder() {
        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);
    }
}

Output

c
a
Z
Y
B
A
9
4
1

2. List Objects

1.1 Sort by age, natural order.

package com.favtuts.java8.stream;

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

public class StreamSortList {

    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) {
        sortListObjectUserByAgeNaturalOrder();
    }

    static void sortListObjectUserByAgeNaturalOrder() {
        /*
         * 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 +
                    '}';
        }
    }
}

Output

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}

1.2 reverse order.

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

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

Output

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}

1.3 Sort by name

        /*
         * 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());

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

Download Source Code

$ git clone https://github.com/favtuts/java-core-tutorials-examples

$ cd java-basic/java8/stream

References

• Java 8 Lambda : Comparator example
• Java 8 – How to sort a Map
• Stream sorted docs