Difference Between HashMap and HashTable in Java

There is no significant Difference Between HashMap and HashTable. HashMap and Hashtable store keys and value couples in a hash map. When using a Hashtable or HashMap we specify an object using a key and the value you want to be linked to this key. 

What is the Difference Between HashMap and HashTable?

HashMap is not synced. It is not thread-safe and cannot be shared between several threads without proper synchronization code whereas hashtable is synchronized. 

For example, hash maps allow a single null number and several null values. Hashtable does not accept null numbers or keys. Because null is not an object, objects used as keys should implement hashCode and equal methods.

The following text describes the main Difference Between HashMap and HashTable.

What is a HashMap?

HashMap Example

A HashMap is a data structure that maps keys to values. Keys and values can be of different types: strings, integers, floats. 

A HashMap maps keys to values, a hash function is used for this purpose. The hash function takes the keys and return an integer.

A HashMap is a data structure that enables fast look-up of a key in a collection. It was originally developed for the Map interface pattern, which allows any collection of key and value pairs to be used as a Map. 

HashMap has two parameters: ‘size’, the maximum number of entries, and ‘loadFactor’, the fraction of the entries that must be loaded into the bucket array to ensure that all keys will be able to be accessed. HashMap is a class in the java.util package.

A HashMap is an implementation of Map interface using an associative array or dictionary implementation for the values. HashMaps are one of the most commonly used data structures. 

They are used where a value can be looked up or stored based on its key. A HashMap allows a value to be looked up quickly but not necessarily found.

It is an unordered collection where the elements have no particular order. A HashMap is used to implement the Map interface in Java and for many other data structures. 

HashMaps are associative arrays for storing key value pairs in a way that allows for fast searching and accessing.

What is a Hashtable?

Hashtable Example

One of the most common data structures in the Java Platform is the Hashtable, a collection that stores key-value pairs. The Hashtable is a dynamic size collection that stores a collection of key-value pairs. 

It works by allocating a fixed amount of memory to the table and then using an internal hashing algorithm to map the given key into some location in the table. The table is then sorted by the key.

A hashtable is a data structure where key-value pairs are stored. The keys are strings of characters and the values are arbitrary objects. The keys are often represented as integers. 

The Hashtable class in Java is a Hashtable implementation of the Map interface which allows access by index (for lookup by key rather than binary search) and has an API that is somewhat similar to that of Map, but it does not support multiple value objects per key.

A Hashtable is a type of data structure used to store and retrieve data. It is a mapping of keys (entries) to values (the values may be objects, strings or any other type). 

There are two important ways in which the Hashtable can be used: as a collection of key/value pairs, and as a set of names, each associated with its value. 

The purpose of Hashtable is to help you design and develop programs that need a way to manage data.

A Hashtable is a data structure associated with a linked list. Hashtables are designed to represent collections of key/value associatide pairs, and are used in many different programming and scripting languages. 

The key is used to look up the value. A key can be a string or its corresponding integer representation.

A Hashtable is an abstraction of an associative array. An associative array is a data structure that associates keys with values. 

Keys can be of any type. Values can be of any type (that is, they need not be scalar); you can have multiple values associated with a single key.

Tell me the Difference Between HashMap and HashTable?



It allows a single null number and several null values.

It does not accept null numbers or keys.

It is not synced.

It is synchronized.

It is a data structure where key-value pairs are stored.

It is a type of data structure used to store and retrieve data.

HashMap works for small-to-medium sized sets of data.

It works for big sets of data.

HashMap is a modern implementation.

Hashtable is a legacy data structure.

HashMap uses a sorted list of keys as its internal data structure.

Hashtable uses an array for the data structure.

Advantage of a HashMap is that a map is ordered.

Hashtable is more memory efficient.


There is no significant difference between the two. Each of them has a list of names for each key and value. The Difference Between HashMap and HashTable is that HashMap uses a sorted list of keys as its internal data structure, whereas Hashtable uses an array for it. 

HashMap and Hashtable are both Java data structures. They both implement the Map interface. HashMap is an unordered associative array and Hashtable is an ordered associative array. An unordered map can get data quickly but you need to know which key was used to get the data.

Hashtable is more memory efficient, but the advantage of a HashMap is that a map is ordered.

HashMap is a general-purpose container that maps keys to values. It contains key-value pairs, which are typically integer or String keys and String or Integer values. It also supports null keys and values. It is intended to be a generic data structure for storing key-value pairs.

HashMap and Hashtable are data structures. HashMap works for small-to-medium sized sets of data. Hashtable works for big sets of data. HashMap is a Java implementation of Google Map.

The HashMap class extends the Hashtable class (which provides a simple implementation of a hash table) by providing an additional method “getOrSet” which will be invoked every time a key is inserted in the table.

HashMap is designed for storing a collection of objects, while Hashtable is designed for storing a collection of ints or strings. One of the most fundamental differences between the two is that HashMap is not ordered and HashTable is not synchronized.’

Hashtable and HashMap are two classes that are used to manage objects in J2SE 5.0 and higher. They are both implemented as hashtables. There is a Difference Between HashMap and HashTable, which is a bit hidden by the different implementations. In short, a Table object is usually optimized to have smaller memory footprint for small number of entries, HashTable is optimized for large number of entries.

When should I use HashMap and Hashtable?

Hashtable is a legacy data structure, and HashMap is a modern implementation. The choice depends almost entirely on your priorities. 

For example, if you need to save money to buy a car, you’ll want to buy an old, reliable car. If you need a fast car, you’ll want to buy a new, unreliable model.

It really isn’t clear in all cases. The Java API provides HashMap, and Hashtable, but it is unclear why the API provides them, and what they are good for. 

If you ask a Java programmer, they will tell you they provide lookup. But there is no lookup.

Use HashMap and Hashtable when you expect to be looking up values in the map frequently, so the overhead of using a hashset is not a concern. If you are only doing a few lookups per iteration, use a hashset. 

Otherwise, use the map or the Hashtable. When you expect to be searching the list, use the list rather than the Hashtable or the HashMap.

Java HashMap vs Hashtable

Hash functions are used in data structures like HashMap and Hashtable for fast retrieval of data stored in the data structure. The goal of using hash functions is to do so efficiently. 

Although hash functions are not unique to the two data structures, it is for the most part, due to the implementation differences, that hash functions can be used in both the structures.

The java HashMap stores and manipulates key-value mappings of a generic type but it requires more memory and a different data structure compared to the Hashtable.

The Java HashMap is an associative array, or a data structure that stores key/value pairs. 

A key is the index of an entry in the data structure. A value is the data associated with any key. It stores all the values for a particular key.

You can implement the Map interface for your own data structure. It is not necessary to use the Collections class. 

It is a collection that does not impose any order on its elements, and they are accessed by an integer index. It does not maintain any order, and therefore it is not a ‘

A Hashtable is a dynamic hashmap which means you are able to create the array and also to add and remove elements and their order. 

It is very useful for fast searching and also to add the number of elements and access in an efficient manner. The hash table is an implementation of the hash map. 

But the one difference between a hash map and a hash table is that the hash table implements the map interface so that the hash table can be used as a map.

Hashtable Declaration

Hashtables are commonly used to store data. Hashtable creates an array of buckets each of which contains a number of key-value pairs. 

For example, using the key-value pairs hash table, an array of buckets may be created and then the data can be inserted into the hash table. 

The java.util.Hashtable class provides a mapping between key/value pairs, and is one of the most basic of all classes. It offers a large number of useful methods and properties that can be used to manage a table of key/value pairs. 

A hash table is an efficient data structure with which to store key/value pairs. Using a hash table allows for fast lookup of any key of a specific value. 

This is done by using each key as an index into the array which stores the value. It’s important to note that this is very different from a HashMap.

HashMap Declaration

The HashMap class is a generic class, and so it can hold any type of data. The HashMap also implements the Map interface, which makes it easy to add and remove elements, and get and put values. 

To declare a HashMap instance, use the new keyword and give it a name with a parenthesis after it. The HashMap is not initialized by the constructor, so use the no-arguments constructor to create it.

It contains three methods: a put () method to add keys (strings) and values (ints), a get () method to return a value if the key is found, and a clear () method to remove all elements from the map, so that the size of the map is 0.

A hash map is a data structure for storing a collection of key/value pairs. A hash map is commonly used in a key-value store or index. The keys in a hash map are typically strings, but they can be any type that can be compared for equality. 

Hash maps are useful when you want to quickly look up or store a value based on a key.

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