Reversing an Arraylist Example in Java

Introduction

Reversing an ArrayList is a classic Java console program that demonstrates the concept with complete source code and sample output. The Collections Framework provides ArrayList, HashMap, HashSet and related data structures.

This tutorial walks through the program line by line, explains how the logic works, and highlights best practices you can apply in your own code.

Definition

An ArrayList is a non-syncronized class. It implements List Interface and inherits AbstractList class. It maintains insertion order. The Collections class contains a default method ‘reverse’ to reverse the order of ArrayList.

Syntax

Collections.reverse(arraylist);

Reverse an ArrayList Example Program

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

class ReversingArrayList{
	public static void main(String[] args){
		ArrayList<String> arraylist = new ArrayList<String>();
		
		arraylist.add("NORTH");
		arraylist.add("SOUTH");
		arraylist.add("EAST");
		arraylist.add("WEST");
		
		System.out.println("Arraylist is : "+arraylist);//Printing actual arraylist
		Collections.reverse(arraylist);//Reversing order of arraylist
		System.out.println("Reversed arraylist is : "+arraylist);// Printing arraylist after reversing
	}
}

Sample Output

Arraylist is : [NORTH, SOUTH, EAST, WEST]
Reversed arraylist is : [WEST, EAST, SOUTH, NORTH]

When to use

Use this reversing an arraylist example when learning or revising core Java syntax.

How it works

1. Execution begins in the main method — the JVM calls this method when you run the class.

2. import java.util.ArrayList; imports a class used later in the program.

3. import java.util.Collections; imports a class used later in the program.

4. ArrayList<String> arraylist = new ArrayList<String>(); updates a variable used in the calculation or output.

5. A println / print call writes text to the console — part of the sample output below.

6. A println / print call writes text to the console — part of the sample output below.

7. Compare your console output with the sample output for Reversing an ArrayList to confirm the program behaves correctly.

Best Practices

• Use meaningful variable and class names that describe their purpose.
• Compile and run the program locally — modify values to see how output changes.
• Read compiler errors carefully; they usually point to the exact line to fix.

Common Mistakes

• Copying code without understanding each line — practice by changing one statement at a time.
• Mismatching the public class name and the .java filename.
• Forgetting semicolons at the end of statements.