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Hashtable Vs Hashmap Java: Java Explained

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Java is one of the most popular programming languages in the world and is widely used to develop applications and websites. It’s important to understand its various features and data structures, such as hashtables and hashmaps. In this article, we will discuss the similarities and differences between the two, their specific use cases and how to implement them in Java.

What is a Hashtable?

A hashtable is an unordered collection of data that stores data in key-value pairs. It allows for fast access to elements when the keys used to store data are known. This makes it a very efficient way to store and retrieve data, as the time complexity of a hashtable is O(1) – meaning that the time taken to access elements is the same regardless of the size of the table.

Hashtables offer several advantages: they save memory space as they don’t need to store their keys (the index), they are thread-safe meaning that multiple threads can access the same data without interfering with each other, they can be synchronized to ensure that all threads get updated information, and they offer fast search times.

Hashtables are also very versatile and can be used to store any type of data, from strings to objects. They are also very easy to use, as they can be implemented with just a few lines of code. Furthermore, they are highly scalable, meaning that they can be used to store large amounts of data without any performance issues.

What is a Hashmap?

A hashmap is also an unordered collection of data that stores data in key-value pairs. It essentially works the same way as a hashtable, except for one key difference – a hashmap does not guarantee the order in which its elements will be stored or retrieved. This makes it potentially faster, but less reliable than a hashtable.

Hashmaps are often used when speed is of the essence, such as when searching for a specific item in a large dataset. They are also useful when the order of the elements is not important, such as when storing user preferences. Hashmaps are also commonly used in programming languages such as Java and Python.

What are the Key Differences Between Hashtable and Hashmap?

The primary difference between a hashtable and a hashmap is that hashtables are thread-safe and guarantee the order in which elements will be stored and retrieved, while hashmaps aren’t thread-safe and don’t guarantee the order of elements. This means that a hashmap can offer faster look-up times but with less reliability than a hashtable.

Another notable difference between the two is that a hashtable implements the Map interface while a hashmap doesn’t. This means that a hashmap supports more methods than a hashtable when referring to basic operations, but hashtables can be synchronized more easily.

Hashtables also have a higher memory overhead than hashmaps, as they require more memory to store the same amount of data. This is because hashtables use a linked list to store elements, while hashmaps use an array. This means that hashmaps are more efficient when it comes to memory usage.

When to Use a Hashtable Over a Hashmap?

When it comes to using an unordered collection of data in Java, a hashtable should be used when thread-safety and order are important criteria. Hashtables are thread-safe and elements stored within them are retrieved and stored in the same order that they were added. This makes them ideal for situations where concurrent threads must access the same data but should not modify it.

Hashtables also offer better performance than hashmaps in certain situations. For example, if the data set is relatively small and the number of threads accessing the data is limited, a hashtable can provide faster access times than a hashmap. Additionally, hashtables are more memory efficient than hashmaps, as they do not require the additional overhead of a hashmap’s internal buckets.

When to Use a Hashmap Over a Hashtable?

A hashmap should be used when thread-safety and order are less important criteria. As a hashmap does not implement the Map interface, it cannot be synchronized as easily as a hashtable and elements stored within it may not be retrieved and stored in the same order that they were added. This makes them ideal for situations where two concurrent threads may both access and modify the same data.

Hashmaps are also more efficient than hashtables in terms of memory usage and performance. This is because they do not require the overhead of synchronization and can be accessed and modified more quickly. Additionally, hashmaps are not thread-safe, meaning that multiple threads can access and modify the same data without the need for synchronization.

How Do You Implement a Java Hashtable/Hashmap?

To implement either a hashtable or hashmap in Java, you first need to import the relevant classes. For hashtables, you will need to import java.util.Hashtable whereas for hashmaps, you will need to import java.util.HashMap.

From there, you can define a new hashtable or hashmap by simply declaring a variable of type Hashtable or Hashmap. You can then add elements to the collections by using put() or get() methods respectively.

It is important to note that the key-value pairs stored in a hashtable or hashmap must be of the same type. Additionally, the keys must be unique, as duplicate keys will overwrite the existing values.

Pros and Cons of Using a Java Hashtable/Hashmap

Hashtables offer many advantages: they are thread-safe, use minimal memory, scale well with large datasets, and have fast look-up times. However, they do have some drawbacks – they do not store elements in any particular order, which means that retrieval can be unpredictable.

Similarly, hashmaps offer many advantages: they use minimal memory space, provide fast look-up times, and support more methods compared to hashtables. However, they do not guarantee thread-safety nor do they guarantee that elements will be stored or retrieved in any particular order.

When using a Java Hashtable or Hashmap, it is important to consider the pros and cons of each. Hashtables are great for thread-safety and fast look-up times, but may not be ideal for large datasets or when elements need to be stored in a particular order. Hashmaps are great for minimal memory usage and more methods, but may not be ideal for thread-safety or when elements need to be stored in a particular order.

Common Use Cases for Java Hashtables/Hashmaps

Hashtables and hashmaps are commonly used in applications where large datasets need to be rapidly indexed and retrieved. They are also used when frequent lookups need to happen on an already indexed dataset such as searching through directories or catalogs. Finally, they are also invaluable when concurrent threads need to access the same data without interfering with each other.

Hashtables and hashmaps are also used in applications that require data to be stored in a key-value format. This allows for quick lookups of data based on the key, which can be used to store and retrieve data quickly. Additionally, they are often used in applications that require data to be stored in a sorted order, as the hashmap can be used to sort the data quickly and efficiently.

Sarang Sharma

Sarang Sharma

Sarang Sharma is Software Engineer at Bito with a robust background in distributed systems, chatbots, large language models (LLMs), and SaaS technologies. With over six years of experience, Sarang has demonstrated expertise as a lead software engineer and backend engineer, primarily focusing on software infrastructure and design. Before joining Bito, he significantly contributed to Engati, where he played a pivotal role in enhancing and developing advanced software solutions. His career began with foundational experiences as an intern, including a notable project at the Indian Institute of Technology, Delhi, to develop an assistive website for the visually challenged.

Written by developers for developers

This article was handcrafted with by the Bito team.

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