Java - Tutorial

How to reverse an array list in Java

Quiz

Problem Description

How to reverse an array list?

Solution

Following example reverses an array list by using Collections.reverse(ArrayList)method.

Open Compiler

import java.util.ArrayList;
import java.util.Collections;

public class Main {
   public static void main(String[] args) {
      ArrayList arrayList = new ArrayList();
      arrayList.add("A");
      arrayList.add("B");
      arrayList.add("C");
      arrayList.add("D");
      arrayList.add("E");
      System.out.println("Before Reverse Order: " + arrayList);
      Collections.reverse(arrayList);
      System.out.println("After Reverse Order: " + arrayList);
   }
}

Result

The above code sample will produce the following result.

Before Reverse Order: [A, B, C, D, E]
After Reverse Order: [E, D, C, B, A]

Following example is another example of reverse of array.

Open Compiler

public class HelloWorld {
   public static void main(String[] args) {
      int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
      System.out.println("Array before reverse:");
      
      for (int i = 0; i < numbers.length; i++) {
         System.out.print(numbers[i] + " ");
      } 
      for (int i = 0; i < numbers.length / 2; i++) {
         int temp = numbers[i];
         numbers[i] = numbers[numbers.length - 1 - i];
         numbers[numbers.length - 1 - i] = temp;
      } 
      System.out.println("\nArray after reverse:");
      for (int i = 0; i < numbers.length; i++) {
         System.out.print(numbers[i] + " ");
      } 
   }
}

The above code sample will produce the following result.

Array before reverse:
1 2 3 4 5 6 7 8 9 10 
Array after reverse:
10 9 8 7 6 5 4 3 2 1

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