How To Contrary An Arraylist Inwards Coffee Using Recursion - Representative Tutorial

If you lot ever demand to contrary a List inwards Java e.g. ArrayList or LinkedList, you lot should ever exercise the Collections.reverse() method. It's prophylactic as well as tested as well as likely perform ameliorate than the get-go version of the method you lot write to contrary an ArrayList inwards Java. It's too ane of the recommended best exercise to prefer library method instead of writing your own, every bit advised yesteryear groovy Joshua Bloch inwards List of String or List of your ain custom objects.


In a recursive algorithm, a component subdivision calls itself to create the job. After each run yesteryear work becomes smaller as well as smaller until it reaches to the base of operations instance from where programmer starts to current of air down. The base instance is real of import for a recursive algorithm because without this your plan volition never destination as well as you lot volition rapidly run out of retentiveness inwards both Stack as well as Heap.

In social club to contrary a List using recursion our base of operations instance is a listing of ane element. If your listing contains ane chemical cistron as well as thus the contrary of that listing is the listing itself, thus merely furnish it. Now, on each run yesteryear nosotros demand to add together the concluding chemical cistron on the listing into a novel listing called reversed. Once the plan reaches to base of operations instance as well as starts winding down, nosotros terminate upwardly all the elements inwards the contrary order. To adjust that, nosotros direct maintain  used the addAll() method of java.util.Collection class.

Btw, recursive algorithms are quite pop on programming chore interviews. You volition oft uncovering recursive problems similar Fibonacci series, All permutations of String, or reverse String inwards place on written test, telephonic circular or the face-to-face circular of Java interviews.


If you lot are seriously preparing for a programming job, this is the ane theme you lot cannot ignore.  You tin mail away too depository fiscal establishment lucifer Cracking the Coding Interview book, which contains to a greater extent than than 189 Coding problems as well as solution for few to a greater extent than recursive problems. It's ane of the best books for practicing coding problems peculiarly from programming interview perspective.

Java Program to Reverse a List using Recursion

Here is our sample Java plan to contrary a List inwards Java. It demonstrates both practical approach using Collections.reverse() method as well as algorithmic approach yesteryear using recursion. Btw, a recursive method is quite expensive hither every bit for each recursive telephone telephone a novel listing is created, which is held inwards retentiveness until the listing is completely sorted. For a huge listing of 1000000 elements, this tin mail away easily brand plan goes OutOfMemory because the listing volition move created inwards the heap space.

There is too a direct chances of StackOverFlow because each method telephone telephone volition direct maintain to a greater extent than or less infinite on stack memory. Instead of using recursion here, you lot tin mail away exercise iteration to kind the listing inwards place, which volition merely demand a variable to concord ane value to swap the get-go chemical cistron to concluding as well as thus on. The algorithm is similar to what nosotros direct maintain learned spell reversing an array inwards house inwards Java.

import java.util.ArrayList; import java.util.Collections; import java.util.List;   /*  * Java Program to demonstrate how to contrary a List.  * In this example, you lot volition run across ii ways to contrary a List,  * first, using Collections.reverse() method as well as minute  * yesteryear writing your ain method using recursion.   */ public class TestSolution {      public static void main(String args[]) {          List<String> books = new ArrayList<>();         books.add("Beautiful Code");         books.add("Clean Code");         books.add("Working Effectively amongst Legacy Code");          System.out.println("Original social club of List: " + books);          // Easy agency to contrary a List inwards Java, exercise Collections.reverse()         // method, exercise this to contrary ArrayList or LinkedList in         // production         Collections.reverse(books);          System.out.println("The reversed List: " + books);          // Now, let's endeavour to contrary a List using recursion         List<String> output = reverseListRecursively(books);         System.out.println("Reversed listing reversed again: " + output);     }      /**      * H5N1 recursive algorithm to contrary a List inwards Java      *      * @param listing      * @return      */     private static List<String> reverseListRecursively(List<String> list) {         if (list.size() <= 1) {             return list;         }          List<String> reversed = new ArrayList<>();         reversed.add(list.get(list.size() - 1)); // concluding element         reversed.addAll(reverseListRecursively(list.subList(0, list.size() - 1)));         return reversed;     }  }  Output Original social club of List: [Beautiful Code, Clean Code, Working Effectively with Legacy Code] The reversed List: [Working Effectively with Legacy Code, Clean Code, Beautiful Code] Reversed list reversed again: [Beautiful Code, Clean Code, Working Effectively with Legacy Code]

That's all nigh how to contrary a listing inwards Java. You direct maintain seen 2 ways to contrary the list, get-go yesteryear using the Collections.reverse() method, which you lot should exercise to kind whatever List implementation e.g. Vector, LinkedList, CopyOnWriteArrayLis, or ArrayList inwards Java inwards production. The recursive algorithm is merely for educational purpose. There is a labor for you, endeavour to contrary the listing inwards house using an iterative algorithm, for the solution you lot tin mail away depository fiscal establishment lucifer here.

Further Learning
Java In-Depth: Become a Complete Java Engineer
Java Fundamentals: Collections
Data Structures as well as Algorithms: Deep Dive Using Java
Algorithms as well as Data Structures - Part 1 as well as 2
Data Structures inwards Java ix yesteryear Heinz Kabutz

Share this post