How to Add Element to ArrayList in Java: Simple Guide

To add an element to an ArrayList in Java, use the add() method. For example, arrayList.add(element); adds the element to the end of the list.

Syntax

The basic syntax to add an element to an ArrayList is:

• arrayList.add(element); - Adds element to the end of the list.
• arrayList.add(index, element); - Inserts element at the specified index, shifting later elements.

java

arrayList.add(element);
arrayList.add(index, element);

Example

This example shows how to create an ArrayList, add elements to it, and print the list.

java

import java.util.ArrayList;

public class AddElementExample {
    public static void main(String[] args) {
        ArrayList<String> fruits = new ArrayList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add(1, "Orange");
        System.out.println(fruits);
    }
}

Output

[Apple, Orange, Banana]

Common Pitfalls

Common mistakes when adding elements to an ArrayList include:

• Using an invalid index with add(index, element) which causes IndexOutOfBoundsException.
• Trying to add null elements unintentionally.
• Confusing add() with set(), where set() replaces an element instead of adding.

java

import java.util.ArrayList;

public class PitfallExample {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("A");
        // Wrong: adding at index 5 when list size is 1
        // list.add(5, "B"); // This throws IndexOutOfBoundsException

        // Correct way:
        list.add(1, "B"); // Adds at index 1
        System.out.println(list);
    }
}

Output

[A, B]

Quick Reference

Method	Description
add(element)	Adds element to the end of the list
add(index, element)	Inserts element at specified index
set(index, element)	Replaces element at index (does not add)
size()	Returns number of elements in the list

Key Takeaways

Use arrayList.add(element) to add elements at the end.

Use arrayList.add(index, element) to insert at a specific position.

Avoid invalid indexes to prevent exceptions.

Remember add() inserts, set() replaces elements.

ArrayList can hold null elements but use carefully.