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5 Best Data Structures Java Programmer Should Know

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19th Aug, 2022
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5 Best Data Structures Java Programmer Should Know

Data Structures are integral for storing and organising data for operational ease in the device. Data structures are widely and diversely used in multiple fields of Software Engineering or Computer Science. You can manage data in a memory in countless ways, and this is where the usage of data structures comes from. 

There are two types of data structures, namely, primitive and non-primitive data structures. 

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A primitive data structure is a primitive data type, for example, char, int, float, pointer and double. These data structures can hold one single value. On the other hand, non-primitive data structures are of two kinds, i.e. linear and non-linear data structures. 

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In this article, we will discuss the top five data structures essential for Java programmers to know:-

Arrays In Java

An array is an object belonging to a class generated dynamically. The Java array inherited the Object class, which further implements the cloneable and serialisable interfaces. Java arrays can easily store primitive objects and values while creating single dimensional or multidimensional arrays can also be made. Java also provides the feature for anonymous arrays, one that C++ lacks.

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Arrays in Java are advantageous for code optimisation to retrieve and sort data. We can also randomly access any data in any index position. However, an array can store only fixed size of elements. 

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Example of Java Array

Below is an example of a Java array, where an array will be declared, instantiated, initialised and traversed.

//Java Program to show how to declare, instantiate, initialize  

//and traverse the Java array.  

class Testarray{  

public static void main(String args[]){  

int a[]=new int[5];//declaration and instantiation  






//traversing array  

for(int i=0;i<a.length;i++)//length is the property of array  









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Trees In Java

A tree data structure is a collection of entities or objects called nodes linked to each other to simulate or represent a hierarchy. Trees in Java are non-linear as they do not store data in a sequence but a hierarchical structure. Therefore, the elements in this data structure are arranged in levels. The topmost node in a Tree is called the root node. Each of these nodes has data of any type. Each node has some data and the reference or the link to other nodes known as children.

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In programming and Java, the structure of any node is as follows:

struct node  


   int data;  

struct node *left;  

struct node *right;   

Stacks In Java

A primarily used linear data structure to store a collection of objects is called a Stack. It relies on Last-In-First-Out (LIFO) and provides numerous classes and interfaces to store object collections. One of these classes is the Stack class, containing a default constructor for creating an empty stack. The syntax is as follows:-

public Stack() 

To create a Stack, import the java.util package first and then make an object of the Stack class. The syntax is as follows:-

Stack stk = new Stack();  


Stack<type> stk = new Stack<>(); 

(Type indicates the stack type such as String, Integer, and the like.)

The stack data structure also has two integral operations- push and pop. The push method places the item at the top of a stack. It is similar to the addElement(item) method used in the Vector class. A parameter item is first passed to be inserted into the Stack. On the other hand, the pop method omits an object present on top of the Stack, and the same object is returned. If the Stack is empty, it uses the EmptyStackException.

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Queue In Java

The Queue interface is a part of java.util package and further extends the Collection interface. It is primarily used for holding elements run in the FIFO(First In First Out) order. This ordered object list follows the FIFO (First-In-First-Out) principle as it is used to insert elements at the very end of the list and delete elements at the beginning of the list.

For the declaration in this interface, the queue requires a concrete class. The most common among these classes are LinkedList and PriorityQueue; however, neither of these implementations is thread-safe. Therefore, PriorityBlockingQueue is often used as an alternative implementation for thread-safe implementation.

The following can be stated as the Queue interface declaration:

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public interface Queue extends Collection

Linked lists In Java

Linked List is another integral part of the Collection framework in java.util package. The class is another implementation of the LinkedList data structure. It is a linear data structure where elements aren’t stored in adjacent locations. Every element in this data structure is a separate object with the address and data parts. The elements are joined with the help of addresses and pointers, with each of these elements called nodes. Linked Lists are dynamic, with insertions and deletions easily carried out. Therefore, they are often preferred more than arrays. However, the nodes do not offer direct access. Therefore, one needs to start from the head and go through the link to reach a node.


Data Structures are essential for programmers, data scientists and developers working as the building foundations of any computing or digital process. Therefore, it is essential to gain proficiency in any programming language, whether for software development, web development, or data science. Without a strong data structure foundation, you cannot code effectively. Without understanding data structure functionalities, you will fail to write code, handle data, and execute algorithms to solve various coding problems. Therefore, it is integral to have a strong base in data structures if you want to start a career in the software industry or even sit for a technical interview. If you have an urge to learn more about data structures then you can check the course “Master of Science in Computer Science” offered by upGrad.


Pavan Vadapalli

Blog Author
Director of Engineering @ upGrad. Motivated to leverage technology to solve problems. Seasoned leader for startups and fast moving orgs. Working on solving problems of scale and long term technology strategy.

Frequently Asked Questions (FAQs)

1What are linear data structures?

A linear data structure allows the storage of data elements in a sequential manner. Types of linear data structures include arrays, stacks, queues, linked lists and matrices.

2What are non-linear structures?

Non-linear data structures don’t have a sequential linking of the data elements. In a non-linear data structure, a pair or a group of data elements are also sometimes linked because it does not follow a strict sequence for accessing data elements.

3What are trees?

Trees are hierarchical data structures that are non-linear. A tree is an abstract data type that consists of a root node (parent) with multiple other nodes connected to it.

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