Fail-Fast Iterators vs Fail-Safe Iterators

In this post, we will learn the difference between Fail-Fast Iterators and Fail-Safe Iterators in Java. This is a frequently asked question in Java interviews for beginners. Let's dive into it.

Difference between Fail-Fast Iterators and Fail-Safe Iterators in Java

Features Fail-Fast Iterators Fail-Safe Iterators
Modification Fail-fast iterators do not allow modifications to the collection while iterating over it. Fail-safe iterators allow modifications to the collection while iterating over it.
Exception If a collection is modified while iterating over it, these iterators throw a ConcurrentModificationException. These iterators do not throw any exceptions if a collection is modified while iterating over it.
Traversal They use the original collection to traverse the elements. They use a copy of the original collection to traverse the elements.
Memory Usage These iterators do not require extra memory. These iterators require extra memory to clone the collection.
Examples Iterators returned by ArrayList, Vector, and HashMap. Iterator returned by ConcurrentHashMap.

Related Collections Interview QA

  1. map() vs flatMap() in Java
  2. Collections vs Streams
  3. ArrayList vs Vector
  4. Iterator vs ListIterator
  5. HashMap vs HashTable
  6. HashSet vs HashMap
  7. Array vs ArrayList
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  9. HashMap vs ConcurrentHashMap
  10. LinkedList vs ArrayDeque
  11. LinkedList vs Array
  12. LinkedList vs Doubly LinkedList
  13. Enum vs EnumSet in Java
  14. HashMap vs. TreeMap in Java
  15. Synchronized Collections vs. Concurrent Collections

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