Java Comparator.naturalOrder
March 22, 2019
naturalOrder
is the static method of Comparator
functional interface. Comparator.naturalOrder
method introduced in Java 8, returns a comparator that compares Comparable
objects in natural order. For natural ordering, a class needs to implement Comparable
and define compareTo
method. A collection of objects are sorted according to compareTo
method in natural ordering. Java classes such as Integer
, String
and Date
implement Comparable
interface and override its compareTo
method and they are sorted in lexicographic-order.
Find the
naturalOrder
method declaration from Java source code.
static <T extends Comparable<? super T>> Comparator<T> naturalOrder()
Comparator.reverseOrder
method. Here on this page we will provide examples to use Comparator.naturalOrder
with Stream.sorted
, Collections.sort
, List.sort
and Arrays.sort
to sort the collections of objects in natural order.
Contents
Comparator.naturalOrder with Stream.sorted
Stream.sorted
returns a stream consisting of the elements of this stream, sorted according to the provided comparator.
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() + " ")); } }
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; } }
8 10 11 12 15 ----------- Allahabad Kanpur Noida Varanasi ----------- Krishna Mahesh Mohan Ram Shyam ----------- Shyam Ram Mohan Mahesh Krish
Comparator.naturalOrder with Collections.sort
Collections.sort
sorts the specified list according to the given Comparator instance.
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 with List.sort
List.sort
sorts this list according to the given Comparator instance.
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 with Arrays.sort
Arrays.sort
sorts the specified array of objects according to the order induced by the specified comparator.
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() + " "); } } }
References
Interface ComparatorJava 8 Stream sorted() Example
Java Comparator.reverseOrder