來源：公眾號(hào) 作者：Java知音
鏈接：https://mp.weixin.qq.com/s/eHpr84Apj4glyFCAlfxKPQ

naturalOrder是比較器功能接口的靜態(tài)方法讹躯。

Java 8中引入的Comparator.naturalOrder方法返回一個(gè)比較器汰规，該比較器以自然順序比較可比較對(duì)象卷扮。

對(duì)于自然排序，一個(gè)類需要實(shí)現(xiàn)Comparable并定義compareTo方法闪幽。

一個(gè)對(duì)象的集合根據(jù)compareTo方法以自然排序進(jìn)行排序瞎颗。

像Integer监署、String和Date這樣的Java類實(shí)現(xiàn)了Comparable接口并覆蓋了其compareTo方法内列，它們以詞表順序(lexicographic-order)進(jìn)行排序。

從Java源代碼中找到naturalOrder方法聲明恩够。

static <T extends Comparable<? super T>> Comparator<T> naturalOrder() 

為了扭轉(zhuǎn)自然排序卒落，我們可以使用Comparator.reverseOrder方法。

在本頁面中蜂桶，我們將提供一些例子儡毕，說明如何使用Comparator.naturalOrder與Stream.sorted、Collections.sort扑媚、List.sort和Arrays.sort一起對(duì)對(duì)象的集合進(jìn)行自然排序腰湾。

與 Stream.sorted 一起使用

Stream.sorted返回一個(gè)由這個(gè)流的元素組成的流雷恃，根據(jù)提供的比較器進(jìn)行排序。

StreamSortedDemo.java

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
public class StreamSortedDemo {
    public static void main(String[] args) {
        List<Integer> numList = Arrays.asList(12, 10, 15, 8, 11);
        numList.stream().sorted(Comparator.naturalOrder()).forEach(n -> System.out.print(n + " "));
        System.out.println("\n-----------");

        List<String> strList = Arrays.asList("Varanasi", "Allahabad", "Kanpur", "Noida");
        strList.stream().sorted(Comparator.naturalOrder()).forEach(s -> System.out.print(s + " "));
        System.out.println("\n-----------");

        List<Student> stdList = Student.getStudentList();
        stdList.stream().sorted(Comparator.naturalOrder()).forEach(s -> System.out.print(s.getName() + " "));
        System.out.println("\n-----------");

        //reverse order of natural order using Comparator.reverseOrder()
        stdList = Student.getStudentList();
        stdList.stream().sorted(Comparator.reverseOrder()).forEach(s -> System.out.print(s.getName() + " "));
    }
} 

Student.java

import java.util.Arrays;
import java.util.List;
public class Student implements Comparable<Student> {
    private String name;
    private int age;
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public int getAge() {
        return age;
    }
    @Override
    public int compareTo(Student s) {
        return name.compareTo(s.getName());
    }
    public static List<Student> getStudentList() {
        Student s1 = new Student("Ram", 18);
        Student s2 = new Student("Shyam", 22);
        Student s3 = new Student("Mohan", 19);
        Student s4 = new Student("Mahesh", 20);
        Student s5 = new Student("Krishna", 21);
        List<Student> list = Arrays.asList(s1, s2, s3, s4, s5);
        return list;
    }
} 

輸出

8 10 11 12 15 
-----------
Allahabad Kanpur Noida Varanasi 
-----------
Krishna Mahesh Mohan Ram Shyam 
-----------
Shyam Ram Mohan Mahesh Krish 

與 Collections.sort 一起使用

Collections.sort根據(jù)給定的比較器實(shí)例對(duì)指定的列表進(jìn)行排序费坊。

CollectionsSortDemo.java

import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class CollectionsSortDemo {
    public static void main(String[] args) {
        List<Integer> numList = Arrays.asList(12, 10, 15, 8, 11);
        Collections.sort(numList, Comparator.naturalOrder());
        numList.forEach(n -> System.out.print(n + " "));
        System.out.println("\n-----------");

        List<String> strList = Arrays.asList("Varanasi", "Allahabad", "Kanpur", "Noida");
        Collections.sort(strList, Comparator.naturalOrder());
        strList.forEach(s -> System.out.print(s + " "));
        System.out.println("\n-----------");

        List<Student> stdList = Student.getStudentList();
        Collections.sort(stdList, Comparator.naturalOrder());
        stdList.forEach(s -> System.out.print(s.getName() + " "));
    }
} 

與 List.sort 一起使用

List.sort根據(jù)給定的比較器實(shí)例對(duì)這個(gè)列表進(jìn)行排序倒槐。

ListSortDemo.java

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
public class ListSortDemo {
    public static void main(String[] args) {
        List<Integer> numList = Arrays.asList(12, 10, 15, 8, 11);
        numList.sort(Comparator.naturalOrder());
        numList.forEach(n -> System.out.print(n + " "));
        System.out.println("\n-----------");

        List<String> strList = Arrays.asList("Varanasi", "Allahabad", "Kanpur", "Noida");
        strList.sort(Comparator.naturalOrder());
        strList.forEach(s -> System.out.print(s + " "));
        System.out.println("\n-----------");

        List<Student> stdList = Student.getStudentList();
        stdList.sort(Comparator.naturalOrder());
        stdList.forEach(s -> System.out.print(s.getName() + " "));
    }
} 

與 Arrays.sort 一起使用

Arrays.sort根據(jù)指定的比較器引起的順序?qū)χ付ǖ膶?duì)象陣列進(jìn)行排序。

ArraysSortDemo.java

import java.util.Arrays;
import java.util.Comparator;

public class ArraysSortDemo {
    public static void main(String[] args) {
        Student s1 = new Student("Ram", 18);
        Student s2 = new Student("Shyam", 22);
        Student s3 = new Student("Mohan", 19);

        Student[] stdArray = {s1, s2, s3};
        Arrays.sort(stdArray, Comparator.naturalOrder());
        for (Student s : stdArray) {
            System.out.print(s.getName() + " ");
        }
    }
}