Java program to reverse ArrayList

Program

import java.util.ArrayList;
import java.util.Collections;
public class ReverseArrayList {
  public static void main(String[] args) {
    ArrayList arrayList = new ArrayList();
    arrayList.add("Ada");
    arrayList.add("Java");
    arrayList.add("Python");
    arrayList.add("F#");
    arrayList.add("HTML");
    System.out.println("Before Reverse Order: " + arrayList);
    Collections.reverse(arrayList);
    System.out.println("After Reverse Order: " + arrayList);
  }
}

This Java program demonstrates how to reverse the elements of an ArrayList using the Collections.reverse method.

Use Case:

This program is ideal for scenarios where you need to display a list of items in reverse order, such as logs, ranked lists, or timelines.

1. Importing Required Classes:

   • The program imports java.util.ArrayList and java.util.Collections to use the ArrayList class and the reverse method.

2. Creating and Populating the ArrayList:

   • An ArrayList named arrayList is created.
   • Elements are added to the ArrayList using the add() method. The elements in this example are names of programming languages.

3. Displaying the Original List:

   • The System.out.println() method is used to print the ArrayList before reversing.

4. Reversing the ArrayList:

   • The Collections.reverse() method is called with the ArrayList as its parameter.
   • This method reverses the order of the elements in the ArrayList in place (modifies the original list).

5. Displaying the Reversed List:

   • After the reverse operation, the ArrayList is printed again to show the elements in reversed order.

Key Features:

• Usage of Collections.reverse:
  • A simple and efficient way to reverse an ArrayList without manually writing reverse logic.
• Dynamic ArrayList:
  • The program uses ArrayList, which allows dynamic resizing and operations like reversing.
• Ease of Use:
  • The Collections.reverse() method makes reversing straightforward and avoids manual coding of reverse logic.
• Reusability:
  • The method can be applied to any ArrayList, irrespective of the data type.

Output

javac .\ReverseArrayList.java
java ReverseArrayList        
Before Reverse Order: [Ada, Java, Python, F#, HTML]
After Reverse Order: [HTML, F#, Python, Java, Ada]