6 Essential Data Structures Java Programmer should Learn

Hello guys, Data Structure is a building block of programs. It's even said that  "Data Structure + Algorithms= Program". That's why a good knowledge of data structure is very important for any programmers, including Java developers. Data structure gives you the option to store your data so that you can access it based on your requirement. For example, if you want a fast search based upon the username then you can use HashMap, but that's only possible if you know data structure and their implementations in the programming language you are using, and that's what you will learn in this article. 

 Java API provides built-in support for common data structures, essential for writing programs like an array, linked list, map, set, stack, and queue. You don't need to implement these data structures by yourself, you can directly use them in your program, thanks to the rich and efficient implementation provided by Java API. 

This is also one reason why Java is the best programming language. Since data structure is core to any program and the choice of a particular data structure significantly affects both the functionality and performance of Java applications, it's worth an effort to explore different data structures available in Java.

Many of these data structure is part of the hugely popular Java Collection Framework, and almost all Java programs maybe, except hello world make use of Collection in one or another form. 

In this Java tutorial, we will take a look at a standard data structure. Array, linked list, Stack, Queue, Map, Set, and How they are implemented in Java, along with how to use them.

Btw, if you are a complete beginner in the world of data structure and algorithms, then I also suggest you first go through a comprehensive course like Data Structures and Algorithms: Deep Dive Using Java to learn the basics and master it.

Data Structure and Algorithms are vital for becoming a better developer, and any investment you make in terms of your time, money, and learning effort will pay you for a long time to come.

6 Essential Data Structures for Java Developers to Learn

Here is my list of the fundamental data structure from standard Java API and programming language itself, since an array is part of the programming language itself while others are part of the popular Java Collection framework.

With Java 8 coming up with Lambda expression, Functional Interface, and Streams, which is going to give a new life to Java Collection Framework, especially in the context of leveraging multiple core architecture of modern CPU.

It’s high time that beginners make themselves aware of basic data structures available in Java programming and make the best use of them.

1. Array

Java programming language provides built-in support for the array in the language itself. It has a special syntax to declare an array like int[], which is an array of primitive int types. You can create an array of both reference types and primitives. 

Also, unlike the C programming language, an array in Java is bounded, and you will get ArrayIndexOutOfBoundException if you are working with an invalid index. 

Array in Java are also homogeneous, you can not store multiple types of objects in an array-like you can only store a String in a String[], if you try to store Integer, you will get ArrayStoreException at runtime. 

You can check further check Data Structures and Algorithms: Deep Dive Using Java to learn more about array and other essential data structures and algorithms, and more importantly how to use them in Java Program.

2. Linked List

Apart from the array, a linked list is another basic data structure in programming. Java provides a doubly-linked list implementation as java.util.LinkedList, this class can be used whenever a linked list data structure is needed. 

Since LinkedList is part of the Collection framework, it implements Collection and Iterable interface as well, which allows iterating over them. You can check this article to learn more about LinkedList in Java.

And, if you are revising Data structure concepts for FAANG interviews then I also suggest you join this amazing FAANG interview preparation course by Andrei Negaoi on Udemy. It's called Master the Coding Interview: Big Tech (FAANG) Interviews and it will help you prepare for Facebook, Apple, Amazon, NetFlix, and Google interviews.

3. Hash table

The Hash table, map, or dictionary is one of the most versatile data structures I have seen. I happen to use Map every now and then, and fortunately, Java API provides several implementations of Map data structure for different needs like HashMap, Hashtable, and ConcurrentHashMap.

It's also known as map or dictionary data structure, you might have heard about Dictionary in Python, which is the same as Map in Java. 

A map provides you with O(1) functionality for getting a value back if you know the key, which is a very natural use case in most Java applications.

You can further check the Algorithms and Data Structures - Part 1 and 2 courses on Pluralsight to learn more about the Hash table, map, or dictionary data structure in Java.

4. Stack

Java API also provides a Stack data structure implemented as java.util.Stack. This class extends the legacy Vector class for storing elements. Since the stack is a LIFO (Last In, First Out) data structure, it provides a push() method to insert objects and a pop() method to consume elements from the top. 

The stack is quite popular in different programming tasks like evaluating expressions. By the way, don’t confuse Stack data structure with stack memory, which is used to store local variable and method frames in Java.

Btw, if you are refreshing your data structure concepts for Interviews, I also suggest you go through the Data Structures in Java: An Interview Refresher course on Educative to prepare well for your interview.

5. Queue

The queue data structure is also available in the Java collection framework as an interface and a few concrete implementations like ArrayBlockingQueue, LinkedList, and PriorityQueue. 

Though you can also implement Queue by using LinkedList or array, it's much better to use existing classes, which are tried and tested. 

This not only reduces development time but also the overall code quality and performance of your application. BlockingQueue is a thread-safe extension of the Queue interface and can be used to implement producer-consumer patterns in Java.

6. Set

Set is a special data structure, which doesn't allow duplicates. It's a good data structure to store unique elements like Ids, for example, EmployeeId, OrderId, TradeId, etc. Whenever you are storing data that needs to be unique then you can use Set data structure. If you try to insert duplicates Set will not accept it and its method will return false to indicate that insertion has failed.

Java Collection API provides a couple of implementations of Sets like HashSet, TreeSet, and LinkedHashSet, which is more than enough for most situations. Those collections, apart from the beginning set, also provide sorting and insertion order.

If you want to learn more about advanced data structures in Java, I highly recommend you to join Data Structures and Algorithms Specialization on Coursera. This specialization is a collection of 6 amazing Data structure courses to teach you graph, string, list, and many more essential and advanced data structures. 

The best thing about this program is that you get access to 50 algorithmic puzzles on your phone to brush up and level up your algorithmic skill as well 100+ coding problems which are often asked by big tech companies. More importantly, you get instant feedback on whether your solution is correct or not. 

That's all about some of the most essential Data Structures for Java developers.  Apart from these basic data structures, there are a lot more in the Java collection framework, including concurrent data structures like BlockingQueue and ConcurrentHashMap. For a Java developer with any experience level, it's good to explore new collection classes introduced in Java 5 and 6 for making better use of Java API.

Other Data Structure and Algorithms  You may like

• 50+ Data Structure and Algorithms Problems from Interviews (list)
• 5 Books to Learn Data Structure and Algorithms in-depth (books) 
• How to reverse an array in Java? (solution)
• 75+ Coding Interview Questions for Programmers (questions)
• How to remove duplicate elements from the array in Java? (solution)
• 7 Best Courses to learn Data Structure and Algorithms (best courses)
• How to implement a recursive preorder algorithm in Java? (solution)
• 10 Courses to learn Data Structure in Java (courses)
• How to implement a binary search tree in Java? (solution)
• 7 Free Books to learn Data Structure and Algorithms (books)
• Postorder binary tree traversal without recursion (solution)
• 10 Data Structure and Programming courses to crack interviews (courses)
• How to print leaf nodes of a binary tree without recursion? (solution)
• Recursive Post Order traversal Algorithm (solution)
• Iterative PreOrder traversal in a binary tree (solution)
• How to count the number of leaf nodes in a given binary tree in Java? (solution)
• Recursive InOrder traversal Algorithm (solution)
• 10 Free Data Structure and Algorithm Courses for Programmers (courses)
• 100+ Data Structure Coding Problems from Interviews (questions)

Thanks for reading this article so far. If you like this best Java Data Structure tutorial and article, then please share it with your friends and colleagues. If you have any questions or feedback, then please drop a comment.

P. S. - If you are looking for some Free Algorithms courses to improve your understanding of Data Structure and Algorithms, then you should also check the Data Structures in Java for Beginners course on Udemy. It's free and you just need a Udemy account to join this course.