Java Examples - Reversing an array list


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Problem Description

How to reverse an array list ?

Solution

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

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.

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 

java_arrays.htm

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