What Is Hashtable Data Structure in Java?


Larry Thompson

Hashtables are a fundamental data structure that plays a crucial role in computer science and programming. In Java, a hashtable is an implementation of the Map interface, which allows you to store key-value pairs.

It provides a fast and efficient way to retrieve values based on their corresponding keys. In this article, we will explore what a hashtable is, how it works, and its key features.

Understanding Hashtables

A hashtable is also known as a hash map or dictionary in other programming languages. It uses a technique called hashing to store and retrieve data quickly.

The basic idea behind hashing is to map data items to unique indices in an array based on their values. This allows for constant-time complexity for insertion, deletion, and retrieval operations.

Hashtables consist of an underlying array where the data is stored. Each element in this array is called a “bucket” or “slot.”

When you insert a key-value pair into the hashtable, the key undergoes a hashing function that maps it to an index in the array. The value associated with the key is then stored at that index.

Key Features of Hashtables

1. Fast Retrieval

One of the main advantages of hashtables is their ability to retrieve values quickly.

Since the index for each key-value pair is determined by its hash code, retrieving a value based on its key can be done in constant time O(1). This makes hashtables ideal for applications that require frequent lookups or searches.

2. Dynamic Sizing

A hashtable automatically handles resizing as more elements are added or removed from it.

As the number of elements increases beyond a certain threshold (known as the load factor), the underlying array capacity gets increased, resulting in better performance and reduced collisions. This dynamic resizing ensures efficient memory utilization and improved overall performance.

3. Key-Value Pair Storage

Hashtables store data in the form of key-value pairs.

This means that for every unique key, there is a corresponding value associated with it. The key serves as an identifier or a unique reference to retrieve the associated value. Keys in a hashtable must be unique, but values can be duplicated.

Working with Hashtables in Java

In Java, to use hashtables, you need to import the java.util.Hashtable class. Here’s an example of how to create and work with hashtables:

import java.Hashtable;

public class HashtableExample {
   public static void main(String[] args) {
      // Create a new hashtable
      Hashtable<String, Integer> myHashtable = new Hashtable<>();

      // Add key-value pairs
      myHashtable.put("apple", 10);
      myHashtable.put("banana", 20);
      myHashtable.put("orange", 15);

      // Retrieve values based on keys
      int appleQuantity = myHashtable.get("apple");
      int orangeQuantity = myHashtable.get("orange");

      System.out.println("Apple Quantity: " + appleQuantity);
      System.println("Orange Quantity: " + orangeQuantity);

In the above example, we first import the Hashtable class from the java.util package. Then, we create a new instance of the Hashtable using generic types to define the types of keys and values it will hold.

We add key-value pairs using the put() method, where the first argument is the key and the second argument is the value. We can then retrieve the values using the get() method, passing in the key as an argument.


Hashtables are a powerful data structure in Java that allow for efficient storage and retrieval of key-value pairs. They provide fast retrieval, dynamic sizing, and enable you to organize your data in a structured manner. Understanding how hashtables work and their key features will help you make informed decisions when choosing the appropriate data structure for your applications.

Now that you have a solid understanding of hashtables in Java, you can start incorporating them into your programs to improve efficiency and optimize performance.

Discord Server - Web Server - Private Server - DNS Server - Object-Oriented Programming - Scripting - Data Types - Data Structures

Privacy Policy