Java Collections reverseOrder() Method

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Description

The Java Collections reverseOrder() method is used to get a comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface.

Declaration

Following is the declaration for java.util.Collections.reverseOrder() method.

public static <T> Comparator<T> reverseOrder()

Parameters

NA

Return Value

The method call returns a comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface.

Exception

NA

Java Collections reverseOrder(Comparator<T>) Method

Description

The reverseOrder(Comparator<T>) method is used to get a comparator that imposes the reverse ordering of the specified comparator.

Declaration

Following is the declaration for java.util.Collections.reverseOrder() method.

public static <T> Comparator<T> reverseOrder(Comparator<T> cmp)

Parameters

cmp − This is the comparator.

Return Value

The method call returns a comparator that imposes the reverse ordering of the specified comparator.

Exception

NA

Getting Reverse Order Comparator for a List of Integers Example

The following example shows the usage of Java Collection reverseOrder() method. We've created a List object with some integers, printed the original list. Using reverseOrder() method, we've retrieved a comparator and then reversed sorted the list and printed it.

package com.tutorialspoint;

import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;

public class CollectionsDemo {
   public static void main(String args[]) {  
      
      // create a list object
      List<Integer> list = new LinkedList<>(Arrays.asList(-28,20,-12,8));
      System.out.println(list);
      // create comparator for reverse order
      Comparator<Integer> cmp = Collections.reverseOrder();

      // sort the list
      Collections.sort(list, cmp);  

      System.out.println("List sorted in ReverseOrder: ");
      System.out.println(list);
   }
}

Output

Let us compile and run the above program, this will produce the following result.

[-28, 20, -12, 8]
List sorted in ReverseOrder: 
[20, 8, -12, -28]

Getting Reverse Order Comparator for a List of Strings Example

The following example shows the usage of Java Collection reverseOrder() method. We've created a List object with some strings, printed the original list. Using reverseOrder() method, we've retrieved a comparator and then reversed sorted the list and printed it.

package com.tutorialspoint;

import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;

public class CollectionsDemo {
   public static void main(String args[]) {  
      
      // create a list object
      List<String> list = new LinkedList<>(Arrays.asList("A","B","C","D"));
      System.out.println(list);
      // create comparator for reverse order
      Comparator<String> cmp = Collections.reverseOrder();

      // sort the list
      Collections.sort(list, cmp);  

      System.out.println("List sorted in ReverseOrder: ");
      System.out.println(list);
   }
}

Output

Let us compile and run the above program, this will produce the following result.

[A, B, C, D]
List sorted in ReverseOrder: 
[D, C, B, A]

Getting Reverse Order Comparator for a List of Objects Example

The following example shows the usage of Java Collection reverseOrder(Comparator) method. We've created a List object with some Student objects, printed the original list. Using reverseOrder(Comparator) method, we've retrieved a comparator and then reversed sorted the list and printed it.

package com.tutorialspoint;

import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;

public class CollectionsDemo {
   public static void main(String args[]) {  
      
      // create a list object
      List<Student> list = new LinkedList<>(Arrays.asList(new Student(1, "Julie"), new Student(3, "Adam"), new Student(2, "Robert")));
      System.out.println(list);
      RollNoComparator comparator = new RollNoComparator();
      // create comparator for reverse order
      Comparator<Student> cmp = Collections.reverseOrder(comparator);

      // sort the list
      Collections.sort(list, cmp);  

      System.out.println("List sorted in ReverseOrder: ");
      System.out.println(list);
   }
}
class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
   
   @Override
   public boolean equals(Object obj) {
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }

   public int getRollNo() {
      return rollNo;
   }

   public void setRollNo(int rollNo) {
      this.rollNo = rollNo;
   }

   public String getName() {
      return name;
   }

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

class RollNoComparator implements Comparator<Student>{

   @Override
   public int compare(Student o1, Student o2) {
      return o1.getRollNo()-o2.getRollNo();
   }	
}

Output

Let us compile and run the above program, this will produce the following result.

[[ 1, Julie ], [ 3, Adam ], [ 2, Robert ]]
List sorted in ReverseOrder: 
[[ 3, Adam ], [ 2, Robert ], [ 1, Julie ]]