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About Ilias Tsagklis

Ilias Tsagklis
Ilias is a senior software engineer working in the telecom domain. He is an applications developer in a wide variety of applications/services, currently the technical lead in a in-house PCRF solution. Particularly interested in multi-tier architecture, middleware services and mobile development (contact). Ilias Tsagklis is co-founder and Executive Editor at Java Code Geeks.

Reverse order of List example

With this example we are going to demonstrate how to reverse the order of a List. This is provided by the reverse(List list) API method of the Collections class. The ArrayList is used as a List implementation, but the same API applies to any type of List implementation classes e.g. Vector etc. In short, to reverse the order of a List you should:

  • Create a new ArrayList.
  • Populate the list with elements, with the add(E e) API method of the ArrayList.
  • Reverse the elements of the list, invoking the reverse(List list) API method of the Collections.

Let’s take a look at the code snippet that follows:

package com.javacodegeeks.snippets.core;
 
import java.util.ArrayList;
import java.util.Collections;
 
public class ReverseListOrder {
 
  public static void main(String[] args) {

    /*

Please note that the same API applies to any type of 

List implementation classes e.g. Vector etc

*/

    // Create an ArrayList and populate it with elements
    ArrayList arrayList = new ArrayList();
    arrayList.add("element_1");
    arrayList.add("element_2");
    arrayList.add("element_3"); 
    arrayList.add("element_4"); 
    arrayList.add("element_5"); 

    System.out.println("ArrayList elements : " + arrayList);

    // static void reverse(List list) method reverses the order of elements of the specified list.
    Collections.reverse(arrayList);
 
    System.out.println("ArrayList elements after reversing order : " + arrayList);
 
  }
}

Output:

ArrayList elements : [element_1, element_2, element_3, element_4, element_5]
ArrayList elements after reversing order : [element_5, element_4, element_3, element_2, element_1]

 
This was an example of how to reverse the order of a List in Java.

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