Quick Answer: How Does Iterator Remove Work?

Is HashMap Fail Safe?

Iterator on ArrayList, HashMap classes are some examples of fail-fast Iterator.

This is because, they operate on the clone of the collection, not on the original collection and that’s why they are called fail-safe iterators.

Iterator on CopyOnWriteArrayList, ConcurrentHashMap classes are examples of fail-safe Iterator..

Why enumeration is faster than iterator?

In the example of the micro-benchmark given, the reason the Enumeration is faster than Iterator is because it is tested first. 😉 The longer answer is that the HotSpot compiler optimises a whole method when a loop has iterated 10,000 times.

How does an iterator work?

Each of the collection classes provides an iterator( ) method that returns an iterator to the start of the collection. By using this iterator object, you can access each element in the collection, one element at a time. Obtain an iterator to the start of the collection by calling the collection’s iterator( ) method.

Is iterator a class or interface what is its use?

Iterator is an interface. It is not a class. It is used to iterate through each and every element in a list. Iterator is implemented Iterator design pattern.

Is iterator an abstract class?

Each implementation of Iterator is unique to the collection it is iterating. These is not enough common code to warrant an abstract base class. … This combination allows for complete freedom to implement the interface but allows for code reuse in the cases where implementations can use the abstract class.

Can we use iterator in map?

Since all maps in Java implement Map interface, following techniques will work for any map implementation (HashMap, TreeMap, LinkedHashMap, Hashtable, etc.) Iterating over Map. entrySet() using For-Each loop : … So we can iterate over key-value pair using getKey() and getValue() methods of Map.

Why iterator is used instead of for loop?

An iterator solves these problems by providing a generic interface for looping over a set of data so that the underlying data structure or storage mechanism — such as an array- is hidden. … An iterator may be thread safe while a for loop alone cannot be as it is accessing elements directly.

How do you remove the last element of an ArrayList?

We can use the remove() method of ArrayList container in Java to remove the last element. ArrayList provides two overloaded remove() method: remove(int index) : Accept index of the object to be removed. We can pass the last elements index to the remove() method to delete the last element.

Can we remove elements from ArrayList while iterating?

ArrayList provides the remove() methods, like remove (int index) and remove (Object element), you cannot use them to remove items while iterating over ArrayList in Java because they will throw ConcurrentModificationException if called during iteration.

What iterator can throw a ConcurrentModificationException?

The iterators returned by ArrayList iterator() and listIterator() methods are fail fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator’s own remove or add methods, the iterator will throw a ConcurrentModificationException.

How do I get around ConcurrentModificationException?

To Avoid ConcurrentModificationException in multi-threaded environmentYou can convert the list to an array and then iterate on the array. … You can lock the list while iterating by putting it in a synchronized block. … If you are using JDK1.

Why does iterator remove Do not throw ConcurrentModificationException?

ConcurrentModificationException is not thrown by Iterator. remove() because that is the permitted way to modify an collection while iterating. … Removes from the underlying collection the last element returned by this iterator (optional operation). This method can be called only once per call to next().

Is ArrayList thread safe?

ArrayList , on the other hand, is unsynchronized, making them, therefore, not thread safe. With that difference in mind, using synchronization will incur a performance hit. So if you don’t need a thread-safe collection, use the ArrayList .

How do you check if an ArrayList is empty?

ArrayList isEmpty() in Java with example The isEmpty() method of ArrayList in java is used to check if a list is empty or not. It returns true if the list contains no elements otherwise it returns false if the list contains any element.

Why iterator is fail fast?

Fail-Fast iterators immediately throw ConcurrentModificationException if a collection is modified while iterating over it. Where as Fail-Safe iterators don’t throw any exceptions if a collection is modified while iterating over it. Because, they operate on the clone of the collection, not on the actual collection.

Which is better linked list or ArrayList?

LinkedList is implemented as a double linked list. Its performance on add and remove is better than Arraylist, but worse on get and set methods. … Vector and ArrayList require space as more elements are added. Vector each time doubles its array size, while ArrayList grow 50% of its size each time.

Which is better HashMap or Hashtable?

Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones. Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.

Is HashMap thread safe?

HashMap is non synchronized. It is not-thread safe and can’t be shared between many threads without proper synchronization code whereas Hashtable is synchronized. It is thread-safe and can be shared with many threads.