Top 75 Java Interview Questions - Can We Remove an Element from a List While Iterating in Java?
💡 Java Tricky Interview Question 7
Can you remove an element from a `List` while iterating over it in Java? 🤔 Many developers try this and encounter `ConcurrentModificationException`, but why does this happen? In this video, we’ll break it down and show the right way to do it.
🔥 What You’ll Learn in This Video:
✅ Why removing elements while iterating can cause errors
✅ What is `ConcurrentModificationException`, and how to avoid it
✅ Different ways to safely remove elements from a `List`
✅ How `Iterator` and `ListIterator` help in safe removal
✅ Best practices for modifying collections during iteration
📌 Quick Answer:
Yes, you can remove elements while iterating, but not directly using a standard `foreach` loop or `for` loop. Doing so on a `List` backed by an `ArrayList` will throw `ConcurrentModificationException`.
✔️ Safe ways to remove elements while iterating:
1️⃣ Using `Iterator.remove()` – The safest and recommended way.
2️⃣ Using `ListIterator.remove()` – Works for `ListIterator` and allows modifications while iterating.
3️⃣ Using `removeIf()` (Java 8+ Lambda Expressions) – Clean and readable approach for bulk removals.
4️⃣ Using a separate collection to store elements to remove and deleting them after iteration.
⚠️ Important Notes:
⚠️ Never use `list.remove(index)` inside a loop—it shifts elements and causes errors.
⚠️ Using `Iterator.remove()` is the safest way to avoid `ConcurrentModificationException`.
⚠️ Modifying a list while iterating without an iterator leads to unexpected behavior.
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