naturalOrder 是 Comparator 功能接口的静态方法。 Java 8 中引入的 Comparator.naturalOrder 方法，返回一个以自然顺序比较 Comparable 对象的比较器。对于自然排序，一个类需要实现 Comparable 并定义 compareTo 方法。对象集合按照自然排序的 compareTo 方法排序。 Java 类如 Integer、String 和 Date 实现了 Comparable 接口并覆盖了其 compareTo 方法，它们按字典顺序排序。
从 Java 源代码中找到 naturalOrder 方法声明。

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

要反转自然排序，我们可以使用 Comparator.reverseOrder 方法。在此页面上，我们将提供使用 Comparator.naturalOrder 与 Stream.sorted、Collections.sort、List.sort 和 Arrays.sort 以自然顺序对对象集合进行排序的示例。

Comparator.naturalOrder 与 Stream.sorted

Stream.sorted 返回一个由该流的元素组成的流，根据提供的比较器进行排序。
StreamSortedDemo.java

package com.concretepage;
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

package com.concretepage;
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;
  }
}

输出

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

Comparator.naturalOrder 与 Collections.sort

Collections.sort 根据给定的 Comparator 实例对指定列表进行排序。
CollectionsSortDemo.java

package com.concretepage;
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() + " "));	
  }
}

Comparator.naturalOrder 与 List.sort

List.sort 根据给定的 Comparator 实例对该列表进行排序。
ListSortDemo.java

package com.concretepage;
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() + " "));
  }
}

Comparator.naturalOrder 与 Arrays.sort

Arrays.sort 根据指定的比较器产生的顺序对指定的对象数组进行排序。
ArraysSortDemo.java

package com.concretepage;
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() + " ");
	}
  }
}