How to Iterate ArrayList in Java: Simple Syntax and Examples

To iterate an ArrayList in Java, you can use a simple for loop with index, an enhanced for-each loop, or an Iterator. Each method lets you access elements one by one to perform actions or read values.

Syntax

Here are common ways to iterate an ArrayList in Java:

• For loop with index: Use a counter to access elements by position.
• Enhanced for-each loop: Automatically loops through each element.
• Iterator: Use an Iterator object to traverse the list safely.

java

ArrayList<Type> list = new ArrayList<>();

// For loop with index
for (int i = 0; i < list.size(); i++) {
    Type element = list.get(i);
    // use element
}

// Enhanced for-each loop
for (Type element : list) {
    // use element
}

// Iterator
Iterator<Type> iterator = list.iterator();
while (iterator.hasNext()) {
    Type element = iterator.next();
    // use element
}

Example

This example shows how to create an ArrayList of strings and iterate it using all three methods to print each element.

java

import java.util.ArrayList;
import java.util.Iterator;

public class IterateArrayListExample {
    public static void main(String[] args) {
        ArrayList<String> fruits = new ArrayList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Cherry");

        System.out.println("Using for loop with index:");
        for (int i = 0; i < fruits.size(); i++) {
            System.out.println(fruits.get(i));
        }

        System.out.println("\nUsing enhanced for-each loop:");
        for (String fruit : fruits) {
            System.out.println(fruit);
        }

        System.out.println("\nUsing Iterator:");
        Iterator<String> iterator = fruits.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }
    }
}

Output

Using for loop with index:
Apple
Banana
Cherry

Using enhanced for-each loop:
Apple
Banana
Cherry

Using Iterator:
Apple
Banana
Cherry

Common Pitfalls

Common mistakes when iterating an ArrayList include:

• Using a for loop but calling list.get(i) with an index out of bounds.
• Modifying the list (adding/removing elements) while iterating without using an Iterator, which causes ConcurrentModificationException.
• Forgetting to check iterator.hasNext() before calling iterator.next().

java

import java.util.ArrayList;
import java.util.Iterator;

public class PitfallExample {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("A");
        list.add("B");
        list.add("C");

        // Wrong: modifying list during for-each loop causes error
        // for (String s : list) {
        //     if (s.equals("B")) {
        //         list.remove(s); // Causes ConcurrentModificationException
        //     }
        // }

        // Right: use Iterator to remove safely
        Iterator<String> it = list.iterator();
        while (it.hasNext()) {
            String s = it.next();
            if (s.equals("B")) {
                it.remove();
            }
        }

        System.out.println(list); // Output: [A, C]
    }
}

Output

[A, C]

Quick Reference

Summary of iteration methods for ArrayList:

Method	Description	When to Use
For loop with index	Access elements by position using index	When you need the index or want to modify elements by position
Enhanced for-each loop	Simpler syntax to access each element	When you only need to read elements
Iterator	Traverse and safely remove elements during iteration	When you need to remove elements while looping

Key Takeaways

Use a for loop, enhanced for-each loop, or Iterator to iterate an ArrayList in Java.

Avoid modifying the list during a for-each loop; use Iterator's remove method instead.

Enhanced for-each loop is the simplest way to read elements without needing the index.

Always check iterator.hasNext() before calling iterator.next() to avoid errors.