How To Reverse An ArrayList OR LinkedList In Java?

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• In Java, ArrayList or LinkedList can be reversed using by the Collections.reverse () method.
• The Collection Class is a utility class in the java.util package which provides several useful ways to operate on collection classes.
• The collections.reverse () method reverses the elements of the given ArrayList in linear time, that means it has time complexity of O (n).
• The collection .reverse () method takes the list type as an argument.
  You can use this method to reverse any list type like ArrayList, LinkedList or vector.

 

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Java Program To Reverse An ArrayList In Java

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import java.util.ArrayList;
import java.util.Collections;
 
public class ReverseArrayList
{
    public static void main(String[] args) 
    {
        
         
        ArrayList<String> alist = new ArrayList<String>();
                 
        alist.add("Mango");
         
        alist.add("Apple");
         
        alist.add("Grapes");
         
        alist.add("Guava");
         
        alist.add("Orange");
         
        alist.add("Papaya");
         
        alist.add("Kiwi");
         
        //Printing ArrayList elements before reverse
         
        System.out.println(" Elements Before Reverse in ArrayList:");
         
        System.out.println(alist);
         
        //Reversing the Arraylist using Collections.reverse() method
         
        Collections.reverse(alist);
         
        //Printing Arraylist elements after reverse
         
        System.out.println("Elements After Reverse ArrayList  :");
         
        System.out.println(alist);
    }
}

Output:-

Elements Before Reverse in ArrayList:
[Mango, Apple, Grapes, Guava, Orange, Papaya, Kiwi]
Elements After Reverse ArrayList  :
[Kiwi, Papaya, Orange, Guava, Grapes, Apple, Mango]

 

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Java Program To Reverse LinkedList

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import java.util.Collections;
import java.util.LinkedList;
 
public class Main
{
    public static void main(String[] args) 
    {
        //Constructing a LinkedList
         
        LinkedList<Integer> Llist = new LinkedList<Integer>();
         
        Llist.add(26);
         
        Llist.add(87);
         
        Llist.add(181);
         
        Llist.add(421);
         
        Llist.add(631);
         
        Llist.add(261);
         
        Llist.add(91);
         
        //Printing Linkedlist Elements before reverse
         
        System.out.println("LinkedList Elements Before Reverse :");
         
        System.out.println(Llist);
         
        //Reversing the Linkedlist Elements using Collections.reverse() method
         
        Collections.reverse(Llist);
         
        //Printing list after reverse
         
        System.out.println("LinkedList Elements After Reverse :");
         
        System.out.println(Llist);
    }
}

Output:-

LinkedList Elements Before Reverse :
[26, 87, 181, 421, 631, 261, 91]
LinkedList Elements After Reverse :
[91, 261, 631, 421, 181, 87, 26]

 

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