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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
Learn the key differences between HashMap and Hashtable classes in Java, such as synchronization, null keys and values, performance, and inheritance. See examples of how to use and compare these classes in the Java collection framework.
4247. There are several differences between HashMap and Hashtable in Java: 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 ...
- 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.
Nov 1, 2023 · Learn how HashMap and Hashtable are both hash tables that implement the Map interface in Java, but have different features and limitations. See code examples of how to create and use them, and compare their advantages and disadvantages.
Apr 17, 2023 · Learn the differences between Hashtable and Hashmap, two data structures that store key-value pairs in Java. Compare their features, advantages, and disadvantages, and see examples of how to use them.
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The main difference between HashMap and HashTable is their approach to synchronization and thread safety. While HashTable is inherently synchronized, ensuring that only one thread can access it at a time, HashMap is non-synchronized, allowing simultaneous access by multiple threads. This makes HashMap generally faster in single-threaded ...
