Difference Between HashMap and Hashtable

Edited by Diffzy | Updated on: April 30, 2023


Difference Between HashMap and Hashtable

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HashMap is responsible for the execution of the virtual map interface in Java. Performance of a hashtable takes place inside a Hashtable class, which is responsible for mapping key to value. The HashMap and Hashtable implementations in Java run via the map interface. As a result, they are linked to one another in a very intimate way, yet they are also quite distinct from one another in many respects. Both Hashtable and HashMap are collections that implement the Map interface. Therefore they are relatively comparable to one another.

In addition, the put(), get(), delete(), and containsKey() methods all provide performance that is constant in time (1). On the back end, the operation of these approaches is based on a broader idea of hashing that uses buckets for storing data. Neither of these classes keeps track of the order in which the pieces were inserted. To put it another way, it's possible that the item that was added first won't be the one that comes up first when we iterate through the values. But they also have certain peculiarities, and those distinctions might make one of them superior to the other in specific contexts. Let's take a more in-depth look at these discrepancies.

Hashmap vs. Hashtable

The main difference between HashMap and Hashtable is that HashMap allows for duplicate values to be stored for both the key and the value. In contrast, Hashtable does not allow any same value to be stored for either the key or the deal. HashMap is not a concurrent data structure. They make it possible for several threads to access them simultaneously, in contrast to Hashtable, which operates concurrently but does not make it possible for multiple lines to access it simultaneously.

The individual keys and values are stored in a Java program using a data structure called a hashmap. The HashMap class has everything extremely cleanly arranged, including adding new entries, removing old ones, and placing values, so it can handle all of these operations. In addition, the things that can be found in the HashMap are not organized in any certain order at all. HashMap is not thread-safe due to the fact that it permits many threads to access it at the same time. It is essential to be aware that the Hashtable data structure is not supported by JDK versions 1.8 and later. This change was made to improve performance. ConcurrentHashMap, on the other hand, is a fantastic option that can be used in place of Hashtable. In software applications that make use of several threads, ConcurrentHashMap is an option that ought to be explored for implementation.

A hashtable is a data structure in Java that keeps track of all the variables that have been declared. It is never the amount of data that is stored in a hashtable that determines how successful it will be; rather, the load factor is what makes the difference. As a direct consequence of this, the operation of Hashtable is exceedingly slow. Multiple threads are unable to access the Hashtable at the same time. As a result, it is completely secure for usage with a variety of lines. The data structure known as a hashtable is thread-safe, which means that it can be shared by multiple application threads at the same time.

On the other hand, HashMap is not synchronized. Therefore many threads cannot access it without extra synchronization code being written. A thread-safe version of a HashMap may be created by using the Collections. synchronized map() function. We also can generate a custom lock code or make the function thread-safe by using the synchronized keyword.

HashMap does not need synchronization, making it a more efficient alternative to Hashtable in terms of speed and memory use. In a single-threaded application, unsynchronized objects perform much better than their synchronized counterparts in terms of speed.

Difference Table Between Hashmap and Hashtable in Tabular Form

Parameters of comparison HashMap Hashtable
Concurrency HashMap does not support concurrent operations; as a result, it allows several threads to access it, meaning it is not immune to attack from multiple threads. Because it does not let multiple threads to access it, the Hashtable may be used concurrently without endangering its integrity and is safe for multiple threads.
Speed The HashMap operation is carried out at a breakneck pace. The operation of the hashtable is carried out at a very sluggish pace.
Null value acceptance Both the key and value fields in HashMap are able to take the value null. The use of null values in either the keys or the values of a hashtable is not permitted.
Iterator Iterator is quite error-prone and will sometimes throw. ConcurrentModificationException. The enumerator does not have a fail-fast property and does not generate any ConcurrentModificationExceptions.
Class Inheritance AbstractMap class. Dictionary class.
Application Web pages and web apps both make use of the hashmap data structure. Hashtables are used by online spelling checkers as well as applications used in games.

What is HashMap?

Since version 1.2 of Java, the HashMapK, V> data structure has been included in the collection. The Java. Util package has this class in its directory. It offers the actual implementation of the Map interface that is used in Java. It organizes the data into pairs of keys and values, which may be accessed using an index of another data type (e.g., an Integer). The name of one thing is assigned as the key (index) to another item (value). If you attempt to insert the duplicate key, it will substitute the component of the key that corresponds to it.

Java's HashMap is a collection of one-of-a-kind keys and values responsible for executing the map interface's fundamental functions. In the list, Keys appear in the form of indexes; however, in Map, they appear as objects. In addition, each key is only associated with a single value. The HashMap class provides a systematic approach to finding a deal, adding entries, and removing entries from the Map.

Different kinds of builders may be used with the HashMap. HashMap() constructor is a constructor used to empty the HashMap with a default starting capacity and a default load factor. This constructor is used to create an empty HashMap. There are duplicate values stored in a hashmap, and the items discovered in a hashmap are not arranged in any particular order. One example is the public class HashMap K, V>, which extends AbstractMap K, V> and implements Map K, V> while being clonable and serializable.

HashMap(int initial capacity) is a kind of constructor used to clear out a HashMap that has been initialized with a specific capacity and a load factor set by default. In addition, the HashMap may be constructed with an initial capacity and load factor supplied by the HashMap(int initial capacity, float load factor) constructor.

HashMap cannot support parallel operations. Consequently, most of them allow many threads to approach them, and because their behavior is highly ordered, the execution is quick. Generate a new HashMap with the exact prior mapping as the supplied Map using the HashMap(Map? extends K,? boosts V>m) function. This function is used to build a new HashMap. HashMaps are a common component of web pages and apps that run on the web.

What are Hashtables?

A data structure known as a Hash Table holds information associatively. Data is often kept in a hash table in an array, with each data item being assigned a unique index value. The process moves along relatively quickly if we know the index of the data we want to access.

As a result, it transforms into a data structure in which the operations of insertion and search are performed exceptionally quickly regardless of the volume of the data. A hash table stores its data in an array, and the hash algorithm is used to provide an index that specifies where new data should be added or where existing data should be located from.

Hashtable is a concurrent data structure that gets most of its execution from a class named Hashtable, which maps the key to the values. Because Hashtable operations are performed in parallel, it is impossible for different threads to confront one another directly. Hashtable is relatively easy to implement and contains values identical to one another. Additionally, an actual map interface execution in Java is carried out by it.

If the keys in the Hashtable are discovered to be strings, the hash function will transform them into numerical. On the other hand, if the input key is found to be numbered, the Key mod TableSize algorithm will be used. Even though the hash function is simple to calculate, the pace at which the Hashtable is executed is painfully sluggish. The vast size of the Hashtable and the fact that it does not allocate space for the keys are to blame for the slow performance.

A hashtable is used to carry out the insertion and locate certain activities on average in a consistent amount of time. The importance of the load factor, as opposed to the total amount of objects in the Hashtable, cannot be overstated. When working with a Hashtable, it is essential to have a load factor and hash function that is appropriately selected and an excellent TableSize value.

There is also a second hash function included in the Hashtable, and this one is employed for the resolution of collisions. Hashtables are put to use in the execution of symbol tables in compilers, in the role of transposition tables in gaming systems, and in online spelling checkers.

Main Differences Between HashMap and Hashtables in Points

  • HashMap cannot support parallel operations. Therefore, many threads can approach them, in contrast to Hashtable, which operates concurrently and does not let multiple threads do so.
  • The Iterator is a fail-fast iterator that sometimes throws a ConcurrentModificationException, while the Enumerator is not a fail-fast iterator and never throws a ConcurrentModificationException.
  • HashMap does not include any duplicate values, however, Hashtable does contain values that are identical to one another.
  • Hashmap is more methodical and well-organized than its counterpart, Hashtable, which is straightforward but not well-organized.
  • When using Hashmap, the execution is carried out at a rapid pace, however, when using Hashtable, the execution is carried out at a more leisurely pace.
  • HashMap does not support synchronization. In contrast to Hashtable, which is synchronized, it is not thread-safe and cannot be shared across many threads without the use of appropriate synchronization code. It is safe for use in many threads, and its use is not restricted.
  • In contrast, Hashtable does not permit either a single or numerous null keys or values, but HashMap can.
  • If synchronization between threads is not required, the use of HashMap is often recommended over HashTable.


HashMap and Hashtable are two different names for the same thing: the fundamental map interface execution in Java. A hash map is a container that stores a collection of key-value pairs and ensures that there are no copies of any of the items in the collection. An item in a HashMap is composed of a key and its reserved value. The entries in a HashMap are not ordered, and the majority of them have a high execution speed. Hashtable is a table that associates keys with values and monitors the variables that have been defined in Java. However, because it is not structured, its execution speed is slow.

While HashMap and Hashtable are both capable of performing many of the same tasks, there are significant differences between the two. HashMap and Hashtable are two data structures that have a wide range of practical applications. For example, they are used in the creation of web pages and web applications, as well as in the programming of games, compilers, and online spelling checks.

The objects that are used as keys in a HashTable need to have the hashCode method and the equals method implemented for the table to be able to store and retrieve items effectively. Because null is not an object, it is unable to carry out the actions associated with these methods. HashMap is an upgraded and much-improved version of the original hashtable. HashMap was developed at a later time.


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"Difference Between HashMap and Hashtable." Diffzy.com, 2024. Sun. 21 Apr. 2024. <https://www.diffzy.com/article/difference-between-hashmap-and-hashtable-906>.

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