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Table of contents
1.
Introduction
2.
What is collections reverseOrder() function in Java?
3.
Parameter
3.1.
Returns
4.
How can we sort Collections in reverse order without using the method?
4.1.
Example :
4.2.
Java
5.
How can we sort the collection in reverse order with Collections ReverseOrder()?
5.1.
Example :
5.2.
Java
6.
Frequently Asked Questions
6.1.
How do I reverse a collection list?
6.2.
How do you reverse order a set in Java?
6.3.
Give examples of collection interfaces in Java.
7.
Conclusion
Last Updated: Mar 27, 2024
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Collections.reverseOrder() Method in Java with Examples

Author Nagendra
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Introduction

"reverseOrder() method" is a powerful utility in Java Collections, offering a convenient way to reverse the natural ordering of elements in a collection. This method allows developers to easily sort objects in descending order without implementing custom comparators.

A collection in Java is a framework that provides an architecture for manipulating and storing a set of objects. It includes a number of static methods for manipulating data structures. The Java.util package contains all the classes for the Collection framework.

reverseorder method java

This blog explains the details of the collections reverseOrder() method in Java and its example.

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What is collections reverseOrder() function in Java?

The collections reverseOrder() function is the method of collection class in Java. This function returns a comparator. This comparator is used for the reverse ordering of objects of the collection class. It is a predefined comparator used for sorting objects in reverse order.

Syntax:

public static <DataType> Comparator<DataType> reverseOrder()  
public static <DataType> Comparator<DataType> reverseOrder(Comparator<DataType> comp) 

 

Let's understand the use of the collections reverseOrder() method using some examples. Try it by yourself on online java compiler.
Must Read  C Program to Reverse a Number

Also see, Swap Function in Java

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Parameter

Parameter Description
None No parameters are required.

The reverseOrder() method does not take any parameters. It operates solely based on the natural ordering of elements.

Returns

Returns Description
Comparator A comparator that imposes the reverse of the natural ordering.

It returns a Comparator object that imposes the reverse of the natural ordering of elements. This means that when used with sorting methods like Collections.sort() or Arrays.sort(), it will sort elements in descending order instead of ascending order.

How can we sort Collections in reverse order without using the method?

You can sort Collections in reverse order without using the collections reverseorder() function. You have to create a user-defined comparator. This user-defined comparator will compare the results and return the greater value.

ort Collections in reverse order Image

 Let's have a look at a small example:

Example :

Code:

  • Java

Java

import java.util.*;
class HelloWorld {
      public static void main(String[] args) {
       Vector<Integer> v = new Vector<Integer>();
       //Adding elements to the collections
       v.add(10);
       v.add(40);
       v.add(-90);
       v.add(100);
       System.out.println("The elements present in vector Collection Class are:");
       for(int i : v)
           System.out.println(i);
      //using a user-defined comparator to sort Collection in reverse order
       Collections.sort(v,new Comparator<Integer>() {
    public int compare(Integer a, Integer b) {
        return b.compareTo(a);
    }
});
       System.out.println("The elements present in vector Collection Class after reversing are:");
       for(int i : v)
           System.out.println(i);
   }
}


Output:

The elements present in vector Collection Class are:
10
40
-90
100
The elements present in vector Collection Class after reversing are:
100
40
10
-90

 

Explanation:

In the above code snippet, we have created a comparator to sort the vector collection in reverse order. This user defined comparator works the same as the collection reverseorder() function works. 

How can we sort the collection in reverse order with Collections ReverseOrder()?

In the previous example, we have defined a comparator to sort the vector collection in reverse order. Let's now learn to use the Collections ReverseOrder() function to sort the collection in reverse order.

sort the collection in reverse order with Collections ReverseOrder Image

Example :

Code:

  • Java

Java

import java.util.*;
class HelloWorld {
   public static void main(String[] args) {
       Vector<Integer> v = new Vector<Integer>();
       //Adding elements to the collections
       v.add(10);
       v.add(40);
       v.add(-90);
       v.add(100);
       System.out.println("The elements present in vector Collection Class are:");
       for(int i : v)
           System.out.println(i);
      //using a user-defined comparator to sort Collection in reverse order
       Collections.sort(v,Collections.reverseOrder());
       System.out.println("The elements present in vector Collection Class after using collection reverseOrder() are:");
       for(int i : v)
           System.out.println(i);
   }
}

Output:

The elements present in vector Collection Class are:
10
40
-90
100
The elements present in vector Collection Class after using collection reverseOrder() are:
100
40
10
-90

 

Explanation:

In the above code snippet, we had used the Collections ReverseOrder() function to sort the collection in reverse order. This function returns a comparator used for sorting the collection. 

Also see, Hashcode Method in Java.

Frequently Asked Questions

How do I reverse a collection list?

To reverse a collection list in Java, you can use the Collections.reverse() method. It reverses the order of elements in the list.

How do you reverse order a set in Java?

To reverse the order of a set in Java, you can convert the set to a list, use Collections.reverse() to reverse the list, then convert it back to a set.

Give examples of collection interfaces in Java.

Set, Queue, Deque, and List are examples of Java collection interfaces.

Conclusion

In this article, we have discussed the details of the collections reverseOrder() method in Java and its example.

We hope that the blog has helped you enhance your knowledge regarding the collections reverseOrder() method in Java. You can refer to our guided paths on the Coding Ninjas Studio platform to learn more about DSADBMSCompetitive ProgrammingPythonJavaJavaScript, etc. To practice and improve yourself in the interview, you can also check out Top 100 SQL problemsInterview experienceCoding interview questions, and the Ultimate guide path for interviews. Do upvote our blogs to help other ninjas grow. Happy Coding!!

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