Hash Table vs STL Map. ** Both HashTable and HashMap implements Map interface.
Map is an important data structure. {1->”Hello”, 2->”Hi”, 3->”Bye”, 4->”Run”}

So collections.synchronizedMap(new HashMap()) makes the hashmap only thread safe, rest of its feature remains same. When hash table operations cost time Hash collisions If all our keys caused hash collisions, we'd be at risk of having to walk through all of our values for a single lookup (in the example above, we'd have one big linked list). It will throw NullPointerException. HashMap is not thread-safe. Le framework Collection a ses propres interfaces… Lire plus . At entry level Java programmer, you can expect this interview question on Hashtable vs HashMap.Though the question becomes really easy when you know other concepts like how hashmap works, yet after getting a many queries from my blog readers who are preparing for or working at junior level, I have decided to summarize my knowledge on differences between HashMap and a Hashtable. In short it maintains the mapping of key & value (The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls.) Dynamic array resizing Suppose we keep adding more items to our hash map. HashTable est une … Hashtable vs HashMap in Java Hashtable and HashMap are two hash based collection in Java and used to store objects as key value pair. As this example code shows, HashMap and Hashtable are programmatically similar. As this example code shows, HashMap and Hashtable are programmatically similar. (I’m going to assume this is a self-balancing binary-search-tree, and I’m also going to assume that you meant hash-table). This article focus on : Compare and contrast Hash table and an STL Map. Hashmap allows one null key and many null values, while hashTable doesn't allow any null key or value. There are quite a few examples which I have written before on How to Implement Threadsafe cache, How to convert Hashmap to Arraylist?. We have already discussed other popular java interview questions like ArrayList vs Vector and Comparator vs Comparable.This question is generally asked in java intereview to check whether candidate understand correct usage of collection classes and has knowledge of alternative solutions. Hashtable Hashtable is basically a data structure to retain values of key-value pair. We use it everyday and almost in all applications. HashMap vs. Hashtable similarities Both the Hashtable and HashMap implement the Map interface and both share the same set of methods used to add, remove and manipulate elements of a key-value, pair-based collection class.