Java Academy · Lesson

Iterators & Enhanced for

Traverse collections with Iterator and enhanced for. Learn safe removal during iteration and common pitfalls.

Lesson 2 of 38 steps

Iterators & Enhanced for is a free Java Academy lesson on CoddyKit. This is lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Java Academy learning path, and your progress syncs across the web and the CoddyKit app. The Java Academy course includes 3 lessons in total.

Overview

Iterator gives step-by-step control to walk through a collection. Enhanced for (for-each) is shorter and clean for reading elements. Use Iterator when you need to remove safely during traversal.

Iterator vs for-each

Iterator: use when you may remove items or need fine control.
Enhanced for: best for read-only loops.
Never structurally modify the collection inside enhanced for.

Code: basic Iterator

Iterator uses hasNext() and next(). Each call to next() moves forward and returns the element.

public class Main {
  public static void main(String[] args) {
    java.util.List<String> names = new java.util.ArrayList<>();
    names.add("Ada"); names.add("Bob"); names.add("Cyd");

    java.util.Iterator<String> it = names.iterator();
    while (it.hasNext()) {
      String s = it.next();
      System.out.println(s);
    }
  }
}

Pitfall

Pitfall: Removing directly inside an enhanced for loop often throws ConcurrentModificationException. Use Iterator for safe structural changes.

Code: safe removal

Safe removal: call remove() on the Iterator right after next() when a match is found.

public class Main {
  public static void main(String[] args) {
    java.util.List<String> words = new java.util.ArrayList<>();
    words.add("to"); words.add("be"); words.add("or"); words.add("not");

    java.util.Iterator<String> it = words.iterator();
    while (it.hasNext()) {
      String w = it.next();
      if (w.length() <= 2) {
        it.remove(); // safe removal
      }
    }
    System.out.println(words); // [not]
  }
}

Code: enhanced for/forEach

Enhanced for is clean for reading. forEach with a lambda is another short style (Java 8+).

public class Main {
  public static void main(String[] args) {
    java.util.Set<String> tags = new java.util.HashSet<>();
    tags.add("java"); tags.add("collections"); tags.add("oop");

    // enhanced for: read-only
    for (String t : tags) {
      System.out.print("[" + t + "]");
    }
    System.out.println();

    // Java 8+ forEach
    tags.forEach(t -> System.out.println("tag=" + t));
  }
}

Iterator removal check

Quick check: How do you safely remove elements while iterating a List?

Answer it in the interactive lesson

Recap

Recap: Use enhanced for for simple reads. Use Iterator when you must remove items during traversal. This prevents runtime errors.

Free to start

Learn Java with an AI tutor — free

Write and run real code in your browser, get instant help from a 24/7 AI tutor, and pick up where you left off on the web or in the app.

Courses: 104
Lessons: 374

Start learning free View the full course

Frequently Asked Questions

Is the “Iterators & Enhanced for” lesson free?

Yes — the full text of “Iterators & Enhanced for” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Java Academy course, upgrade to CoddyKit PRO. The Java Academy course includes 3 lessons in total.

What will I learn in “Iterators & Enhanced for”?

Traverse collections with Iterator and enhanced for. Learn safe removal during iteration and common pitfalls. You practise Java Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Java Academy?

No prior experience is required. Java Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 2 of 3.

How long does the “Iterators & Enhanced for” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Java Academy lesson?

Yes. Every Java Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

← Back to Java Academy