Arraylist Example in Java

Introduction

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

The ArrayList class extends AbstractList and implements the List interface. ArrayList supports dynamic arrays that can grow as needed. Standard Java arrays are of a fixed length. After arrays are created, they cannot grow or shrink, which means that you must know in advance how many elements an array will hold. Array lists are created with an initial size. When this size is exceeded, the collection is automatically enlarged. When objects are removed, the array may be shrunk.

Syntax

ArrayList( )
Or
ArrayList(Collection Variable_name)
Or
ArrayList(Data_type capacity)

ArrayList Example Program

import java.util.*;
class ArrayListExample{
	public static void main(String[] args){
		ArrayList al=new ArrayList();
		System.out.println("Initial size of Arraylist is "+al.size());
		al.add("Hai");
		al.add("Hello");
		System.out.println("Arraylist is "+al);
		System.out.println("New size of Arraylist is "+al.size());
		al.add(1,"How are you");
		System.out.println("New Arraylist is "+al);
		System.out.println("New size of Arraylist is "+al.size());
	}
}

Sample Output

Initial size of Arraylist is 0
Arraylist is [Hai, Hello]
New size of Arraylist is 2
New Arraylist is [Hai, How are you, Hello]
New size of Arraylist is 3

When to use

Use this 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.*; imports a class used later in the program.

3. ArrayList al=new ArrayList(); updates a variable used in the calculation or output.

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

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

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

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.