In this article, we will discuss some important data structures which you must know if you’re a Java programmer. Java is one of the widely used languages in the programming world today. It is used for a variety of different development paradigms including desktop development, Android development, and web development. 

Over the years, Java has evolved to be one of the best programming languages for enterprise application development by providing different frameworks in the web paradigm. So if you want to learn and excel at Java, stick with us for the next few minutes to know about the 4 most important data structures in Java. Without any further ado, let’s get started!

Most Important Data Structures in Java

The following are the 4 most important data structures every Java developer must know.

1. Array

Array is one of the basic data structures and is used to store more than one value in a single variable. It is composed of small contiguous blocks in memory which store these data values. An array has a fixed size. With arrays, there exempts the need of declaring separate variables for the values which can be grouped together to make a meaningful sense.

Note that in arrays, we cannot store the values of multiple data types. We are bound to store the values of the same data type throughout the array. For instance, an array of int can only contain integer values. We cannot store String, float or object of any other data type in an array of int.

Syntax

In Java, we can create an array using the following syntax. We define the data type with square brackets [] which is followed by a variable name.

data_type[] variable_name;

If we wish to create an array of strings, we can do the following:

String[] animals = {"Cat", "Dog", "Lion", "Tiger"};

Usage

We can use an array wherever we wish to group elements or objects of the same data type. This grouping can solve various real-world programming problems and provides an ease of information access, updating, and deletion. 

2. Linked List

A Linked List is a powerful data structure that is also used to store multiple values in a single variable. Unlike arrays, linked list does not have a limitation of memory blocks being contiguous. It is a chain of non-contiguous memory blocks called nodes that are linked together with respect to their addresses. 

Similar to an array, we cannot store values of multiple data types in a linked list. While declaring a linked list, we define the data type which the linked list should entail. Throughout its life cycle, a linked list is bound to store the values of the same data type. 

Syntax

In Java, we can create a linked list using the following syntax. We write the keyword LinkedList followed by a data type in angle brackets <>. This notation is followed by a dynamic memory allocation as follows.

LinkedList<data_type> variable_name = new LinkedList<data_type>();

If we wish to create a linked list of strings, we can do the following:

LinkedList<String> myLinkedList = new LinkedList<String>();

Usage

Similar to arrays, we can also use linked lists in scenarios where we wish to group values that contribute to a similar use case in our program. One dominant advantage of linked lists over arrays is that we can dynamically scale and contract whenever we want. The size/length of the linked list is varying. 

3. Stack

A Stack is a special case of a linked list. It operates on the Last In — First Out (LIFO) concept which means that the values can only be inserted and/or deleted from a single open point. So, at any point in time, only that value in stack is directly accessible which we inserted at the end. In the stack-language, we formally refer to these insertions and deletions as push and pop respectively.

Since a stack is an extension to a linked list, we cannot store values of multiple data types in a stack. While declaring a stack, you define its data type and whenever you attempt to insert values into it, they should be of the same data type.

Syntax

In Java, we can create a stack using the following syntax. We write the keyword Stack followed by a data type in angle brackets <>. This notation is followed by a dynamic memory allocation as follows.

Stack<data_type> variable_name = new Stack<data_type>();

If we wish to create a stack of strings, we can do the following.

Stack<String> myStack = new Stack<String>();

Usage

We use stacks in the scenarios where we wish to reverse an arrangement or undo an operation we last did. For example, in order to reverse a string, we can use a stack to get the job done easily. 

4. Queue

Just like a stack, Queues are also a special case of linked list. The difference lies in the operation concept. A queue works on the First In — First Out (FIFO) concept. It means that it is an open-ended data structure from both ends but with a restriction at each end. At one end, we can only insert values whereas at the other end, we can only retrieve/remove values. 

Similar to stack, we can only store values of the same data type in a queue. 

Syntax

One prominent thing to note here is that in Java, a queue is an interface instead of a class. The other concrete implementations inherit this queue interface and then we can utilize the functionality of a queue. The following are some of the classes which can be created using the queue interface. 

Queue<String> queue1 = new LinkedList<>();
Queue<String> queue2 = new ArrayDeque<>();
Queue<String> queue3 = new PriorityQueue<>();

Usage

We use queues in scenarios where we wish to execute things in order of their occurrence. For example, CPU’s FCFS scheduling algorithm uses a queue data structure to schedule the tasks. 

Key Note

That’s all about some of the most important data structures in Java that every Java developer should know. These data structures are used very frequently in practical programming. Hence, it’s better to get acquainted with these data structures in order to do wonders while programming.

If you wish to learn more about Java, you can check out our collection of Java tutorials.