blog posts

All applications that use data structures implement them differently. The topic of data structures is so crucial that all major universities worldwide have dedicated chapters to teach it.

Interestingly, prominent educational institutions have also developed dedicated videos for working with data structures in different programming languages. Successful Java programmers are all familiar with this concept.

Hence, if you are planning to enter the world of Java programming, you should spend significant time learning data structures.

What is a data structure in Java, and why do we need it?

A data structure is a way of organizing data in computer systems. Data structures are tools for efficiently managing large datasets so that data can be accessed and modified efficiently. Data structures help to write algorithms with less time complexity and better execution order.

When writing an optimal algorithm, we must pay attention to memory and time complexity constraints to ensure the output is acceptable. For this reason, we must have complete information about different types of data structures.

Data structures in programming languages such as Java are an efficient way to manage large amounts of data. They are used in almost all large-scale applications, including operating systems, artificial intelligence systems, and compiler design.

Today, applications are connected with a large amount of data, and this has doubled the complexity of these applications and created many challenges for applications and programmers, the most important of which are the following:

• Processing Speed: As data volume increases, management and processing speeds must also increase. Today’s processors can process large amounts of data in a short time and must implement efficient algorithms to achieve this goal.
• Searching Data: Imagine an online store that has more than 200,000 products. If a program intends to search for a specific product based on certain conditions, it must check the specifications of 200,000 products to return a result. It will slow down the search.
• Multiple requests simultaneously: Imagine millions of users searching for data on a web server; naturally, the probability of server issues increases.

To solve the above problems, developers use data structures in programming languages ​​such as Java. In Java data structures, data is stored and managed so that it can be accessed as quickly as possible during search.

What is the advantage of data structures in Java?

As we mentioned, using data structures helps manage data more effectively and address some of the problems mentioned in the previous paragraph. However, Java programmers use data structures in Java for the following reasons :

• Efficiency: Java data structures significantly improve application performance by storing data in the smallest possible space and processing it at high speed.
• Reusability: The ability to reuse data is one of the most important reasons for using data structures. After implementing a particular data structure, it can be used in different parts of an application. In addition, it is possible to define data structures in libraries and reuse them in other applications.
• Abstraction: In Java, the abstract data type ADT is used to specify the data structure. In the mentioned method, developers can use Java data structures through interfaces (Interfaces) in applications without being concerned with the details of the data structure implementation. The abstract data type provides the highest level of detail hiding.

Classification of data structures in Java

In general, data structures in Java are classified as linear or non-linear (or hierarchical). They have their subcategories. Figure 1 shows the above classification.

Figure 1

• Linear Data Structures: All elements are arranged in linear or sequential order in a linear data structure. The linear data structure is a single-level data structure (Single Level Data Structure) in which the elements are sequentially arranged.
• Nonlinear Data Structures: In a nonlinear data structure, data is not stored in a sequential order as in linear data structures. For this reason, non-linear data structures are multi-level data structures.

Types of data structures in Java

The primary data structures in the Java programming language are the following:

•  Arrays
•  Linked Lists
•  Stack
•  Queue
•  Graph
•  Set

The array data structure in Java

An array is a linear, static data structure that represents a group of similar elements accessible via indices. The first address of the variety belongs to the first element, and the last address belongs to the last piece of the collection. Usually, the size of an exhibition in Java is determined before the data is stored.

An array is the simplest data structure: a collection of elements of the same type, accessed by a common name. The first address of the exhibition refers to the first element, and the last address refers to the previous component of the display. Collections contain simple data of the same type, such as Integer, Float, or User-Defined Data. Also, all parts are the same size. Arrays are stored in contiguous memory locations, and data allocation is performed from the smallest memory location to the largest.

When using arrays, you should pay attention to several important points:

•  Arrays can store data elements of similar, straightforward types, such as int or float, or user-defined types, such as structs and objects.
•  Arrays are considered objects in Java.
•  Indexing (indexing) of array values ​​starts with zero.
•  Before using arrays, we need to define them to store data.
• The storage location of arrays in Java is dynamically allocated in the Heap area.
•  The length of the arrays is determined using the Length method.
•  The array size must be an integer (Int).
•  Random access to array elements is possible in Java.

Arrays in Java can be one-dimensional, two-dimensional, or multi-dimensional. As the number of array dimensions increases, the complexity of defining and accessing data increases, and significant memory is consumed. Figure 3 shows one-dimensional arrays.

In Figure 2, you can see the first element and index on the left and the last component and index on the right. Note that the array indices in Figure 3 start at 0 and end at 4. Here, index zero refers to 126, index 1 to 32, index 2 to 230, index 3 to 21, and index 4 to 200.

 Figure 2

Typically, we use arrays when we know the number of elements and their size in advance, because memory is reserved for arrays before processing begins. For this reason, arrays are classified as static data structures. One essential consideration when using arrays is time complexity. The time complexity for performing various operations on arrays is as follows:

• Access to elements: O(1)
• Sequential search: O(n)
• Binary search if the array is ordered: O(log n)
• Add: O(n)
• Delete: O(n)

Linked List in Java

A linked list in Java is a linear, dynamic data structure that stores a collection of similar data elements called nodes. This type of data structure stores two types of data simultaneously. The first type is the actual value used in the program, and the second type is a pointer to the location of the next element in the list. The first node in the linked list is called Head, and the last node is called Tail. The last part refers to Null and means the end of the linked list.

Linked lists in Java were designed to address certain limitations of arrays. For example, in this data structure, there is no need to preallocate the number of elements, so memory can be allocated at runtime as needed. In addition, inserting and removing components in linked lists is done more straightforwardly. In Java, linked lists can be one-way, two-way, and circular.

Singly Linked List

• As shown in Figure 3, adding values ​​to linked lists uses a forward, one-way traversal. This linked list has a node and a single pointer that points to the next node.

 Figure 3

Doubly Linked List

• Both forward- and backward-linked lists can receive data. For this reason, it has two pointers: one to the previous node and the other to the next node. In a two-way linked list, it is possible to navigate from both ends of the list. Figure 4 shows doubly linked lists.

Figure 4

Circular Linked List

• In a circular linked list, the nodes are connected in a circular fashion. No null nodes exist in this linked list, and any node can be defined as the first node. Also, note that doubly linked lists are a good option for implementing rotating queues. Figure 5 shows a circular linked list.

Figure 5

The time complexity of various operations on linked lists is as follows:

• Traversing elements: O(n)
• Searching for a component: O(n)
• Add: O(1)
• Delete: O(1)

Everyday operations on linked lists include merging two lists, splitting a list, and reversing a list.

Stack in the Java programming language

A stack is an abstract data structure in Java. A stack is a collection of objects that are added and deleted based on the principle of “Last In First Out” (LIFO). Items can be added to the stack at any time, but only the most recently added item can be removed at any time. When a stack is defined as an array or a linked list, it inherits all the properties of the collection or linked list. Figure 6 shows the stack.

Figure 6

Note that the Java programming language stack is an ordered list that supports only insertion and deletion operations from one section: the top of the stack. In general, piles perform operations such as calling nested functions, solving mazes, and matching parentheses. The operations performed on the stack are as follows:

• Push(): Adds an element to the top of the stack.
• Pop(): Removes a part from the top of the stack and returns the removed element from the stack.
• Peek(): Declares or retrieves the top component of the stack without removing it. Sometimes this method is called top ().
• Queue in the Java programming language

The queue is another widely used data structure in Java; it is the opposite of a stack. A line is a collection of objects that performs the process of adding and removing objects based on the principle of “First In, First Out” (FIFO). In the queue data structure, the addition process is always done from the end (Rear) and deletions from the beginning (Front) of the queue. Figure 7 shows the queue data structure in Java.

Figure 7

 Joint operations on queues include the following:

• () Enqueue: adding an element to the end of the string.
• Dequeue(): Returns the first element of the column and deletes it.

The queue is typically used for Breadth-First Search in data structures such as trees and graphs. Columns are used to manage process scheduling in multitasking operating systems, including round-robin algorithms and similar schemes. Also, they are a suitable option for asynchronous data transfer between two approaches.

Developers can use queues in many different ways in their applications. However, two types of columns widely used in Java are circular queues and double-ended queues. Circular lines are implemented and defined in a circular path. The advantage of this data-building model is that it addresses the problem of unused capacity in simple, linear queues. A two-way column in Java allows adding and removing elements from both sides of the column, but not from the middle of the row.

The graph data structure in Java

A graph is a non-linear data structure in the Java programming language, which is made up of the following components:

•  A finite set of vertices is known as a node.
•  Edges are represented by a finite set of ordered pairs in the form (e, v). Here, e represents the number of edges.
• The graph data structure in Java is divided into two categories: directed and weighted graphs, based on their properties.
• The path graph data structure divides graphs into two categories: directed and undirected.
• A directed graph is a set of nodes or vertices connected, where all edges have a direction from one vertex to another.
• The weighted graph data structure divides graphs into two groups: weighted charts and unweighted graphs.
• A weighted graph data structure is a graph in which each edge has a weight. This graph is also known as a labeled graph.
• In the unweighted graph data structure, edges have no weight.

Set

A collection is a unique data structure that differs significantly from other examples because it does not support duplicate values. This data structure is used in Java to store individual elements, such as a unique user identifier (ID) (Figure 8). Java provides several implementations of the Set interface; the most important are LinkedHashSet, HashSet, and TreeSet. These data structures are defined through Java application programming interfaces (Java Collection API).

Figure 8

Last word

We introduced you to the most important data structures for storing and organizing data in Java. This article introduced us to key Java data structures, including arrays, linked lists, stacks, queues, graphs, and collections.

Now that you have basic information about data structures in Java and know what features each of these data structures has in Java and what they are suitable for, you should spend some time and learn how to implement each of these data structures in practice.

FAQ