Which types of collections consume more memory; fail-fast or fail-safe?
In Java, the terms "fail-fast" and "fail-safe" refer to how collections handle concurrent modifications while iterating over them.
Fail-Fast Collections: These collections (like ArrayList, HashMap, etc.) immediately throw a ConcurrentModificationException if they detect that the collection has been modified structurally (e.g., adding or removing elements) while iterating over it. They are generally more memory-efficient because they do not maintain any additional data structures to handle concurrent modifications. They operate directly on the underlying data structure.
Fail-Safe Collections: These collections (like CopyOnWriteArrayList, ConcurrentHashMap, etc.) are designed to allow safe iteration even when the collection is being modified. They achieve this by creating a snapshot of the collection at the time of iteration or by using other concurrency control mechanisms. This can lead to higher memory consumption because they may need to maintain multiple copies of the data or additional structures to manage concurrent access.
In summary, fail-safe collections typically consume more memory than fail-fast collections due to the overhead of managing concurrent modifications and maintaining consistency during iteration.