Search results
Jan 23, 2022 · The java.util.Hashtable is used to create a set of key elements in the hash table. It basically returns a set view of the keys, or we can create a new set and store the key elements in them. Syntax: public Set<K> keySet() K : type of the Keys in the hash table Parameters: The method does not take any parameter. Return Value: The method return
HashMap and Hashtable both implement java.util.Map interface but there are some differences that Java developers must understand to write more efficient code. As of the Java 2 platform v1.2, Hashtable class was retrofitted to implement the Map interface, making it a member of the Java Collections Framework.
- Overview
- Hashtable and Hashmap in Java
- Differences Between Hashtable and Hashmap
- When to Choose Hashmap Over Hashtable
- Conclusion
In this short tutorial, we are going to focus on the core differences between the Hashtable and the HashMap.
Hashtable and HashMap are quite similar – both are collections that implement the Mapinterface. Also, the put(), get(), remove(), and containsKey()methods provide constant-time performance O(1). Internally, these methods work based on a general concept of hashing using buckets for storing data. Neither class maintains the insertion order of the ele...
3.1. Synchronization
Firstly, Hashtable is thread-safeand can be shared between multiple threads in the application. On the other hand, HashMap is not synchronized and can’t be accessed by multiple threads without additional synchronization code. We can use Collections.synchronizedMap() to make a thread-safe version of a HashMap. We can also just create custom lock code or make the code thread-safe by using the synchronizedkeyword. HashMap is not synchronized, therefore it’s faster and uses less memory than Hasht...
3.2. Null Values
Another difference is null handling. HashMap allows adding one Entry with null as key as well as many entries with null as value. In contrast, Hashtable doesn’t allow null at all. Let’s see an example of null and HashMap: This will result in: Next, let’s see how Hashtable is different: This results in a NullPointerException. Adding an object with null as a key also results in a NullPointerException:
3.3. Iteration Over Elements
HashMap uses Iterator to iterate over values, whereas Hashtable has Enumerator for the same. The Iterator is a successor of Enumerator that eliminates its few drawbacks. For example, Iterator has a remove()method to remove elements from underlying collections. The Iterator is a fail-fast iterator. In other words, it throws a ConcurrentModificationException when the underlying collection is modified while iterating. Let’s see the example of fail-fast: This throws a ConcurrentModificationExcept...
We should use HashMapfor an unsynchronized or single threaded application. It is worth mentioning that since JDK 1.8, Hashtable has been deprecated. However, ConcurrentHashMap is a great Hashtable replacement. We should consider ConcurrentHashMapto use in applications with multiple threads.
In this article, we illustrated differences between HashMap and Hashtableand what to keep in mind when we need to choose one. As usual, the implementation of all these examples and code snippets are over on Github.
HashMap. Hashtable. 1) HashMap is non synchronized. It is not-thread safe and can't be shared between many threads without proper synchronization code. Hashtable is synchronized. It is thread-safe and can be shared with many threads. 2) HashMap allows one null key and multiple null values. Hashtable doesn't allow any null key or value.
Nov 1, 2023 · A hash table is a data structure that maps keys to values using a hash function. It can allows fast and easy insertion, retrieval, and deletion of key-value pairs. Two of the most widely used types of hash tables in Java are HashMap and Hashtable, which both implement the Map interface. 1. Overview of HashMap in Java
Jan 8, 2024 · 1. Overview. The difference between Map and HashMap is that the first one is an interface, and the second is an implementation. However, in this article, we’ll dig a bit deeper and explain why interfaces are useful. Also, we’ll learn how to make code more flexible with interfaces and why we have different implementations for the same interface.
People also ask
What is a hashtable vs HashMap?
What is the difference between Hashtables and hash maps in Java?
What is the difference between Hashtable and synchronized Map in Java?
What is a hashtable in Java?
What is the difference between map and HashMap?
What is a hash table in Java?
1. Synchronization (Thread Safe) The primary difference between HashMap and Hashtable is synchronization. HashTable is a thread-safe class and can be shared between multiple threads, while HashMap is not thread-safe. Well, HashMap is not thread safe so don't use HashMap in multi-threaded applications without external synchronization.
