Understanding Data Structures and Algorithms in Java

Understanding Data Structures and Algorithms in Java

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Updated on Oct 12, 2023 17:19 IST

Data Structure in Java is used to store and organize data efficiently while the algorithms are used to manipulate the data in that structure. In this article, we will briefly discuss data structures like arrays, stack, queue etc. as well as sort and search algorithms in Java.

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Data Structures are a way to store and organize data in a computer to be used efficiently. Algorithms are used to manipulate the data in those structures. Developers use them in almost every program or software. Programmers and developers must understand data structure and algorithms as they are the foundation of writing efficient programs. In this blog, we will briefly explain various data structures in Java such as Arrays, Linked lists, Stacks, and Queues that every Java programmer must know. We will also cover the basics of algorithms in Java.

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What are Data Structures in Java?

A data structure is a key concept in the Java programming language. Java developers use data structures to store and organize data. Good knowledge of data structures in Java can help programmers write efficient and optimized Java programs. Data Structures offer many other advantages such as reusability and abstraction.

To learn more about DSA, read our post – what are Data Structures and Algorithms?

There are two types of data structures in Java – linear and non-linear (hierarchical) data structures. Let’s understand each of them.

Linear Data Structures in Java

It is a single-level data structure in which the elements are arranged in sequential or linear order. They are easy to implement as they are arranged in a particular order.

Arrays

In an array data structure in Java, the elements are arranged in contiguous memory locations. All the elements have the same type and size in an array. The elements can be randomly accessed by the index. Below is an image of a one-dimensional array. An index represents element.

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There are three types of arrays:

  • Single Dimensional Arrays
  • Two-dimensional Arrays
  • Multi-dimensional arrays

Syntax to declare an array in Java

 
dataType[] arrayName;
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Also Read: Understanding Data Structures in C: Types And Operations

Also Read: Implementing Array in Java

Linked List

In a linked list data structure in Java, the elements are connected through a series of nodes. Each node consists of the data items and the address to the next node.

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Basic Operations of Linked List

  • Insertion: Add a new element
  • Deletion: Remove an element
  • Traversal: Access every element of the linked list
  • Search: It finds a node in the linked list
  • Sort: Sorts the nodes of the linked list

Also Read: Introduction to Linked List in Data Structure

Stacks

The stack data structure follows the Last In First Out (LIFO) principle to store elements. It means that the last element stored in a stack will be removed first.

It is like a pile of plates in which one plate is kept on top of another. To take the plate at the bottom, you will have to remove all the plates on top.

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Basic Operations of Stack

  • Push: For adding an element to the top of a stack
  • Pop: For removing an element from the top of a stack
  • Peek: Get the value of the top element without removing it
  • IsEmpty: Check whether the stack is empty
  • IsFull: Check whether the stack is full

Also Read: All that you need to know about Stack

Queues

Queue data structure follows the First In First Out (FIFO) principle to store elements. The first element stored in the queue will be removed first. It is like a queue of people at a ticket counter. The person standing first in the queue will get the ticket first.

Basic Operations of Queue

  • Enqueue: For adding an element at the end of the queue
  • Dequeue: For removing an element from the front of the queue
  • Peek: Get the value of the front of the queue, without removing it
  • IsEmpty: Check whether the queue is empty
  • IsFull: Check whether the queue is full

Also Read: Python Vs Java: Which One is Better to Learn First?

Also Read: Queue Data Structure: Types, Implementation, and Application

Hierarchical or Non-Linear Data Structures in Java

Developers can arrange these data structures in a hierarchical order rather than a sequential order. They have a multilevel data structure. Each element will be connected to one (or more) elements.

Binary Trees

A binary tree is a non-linear data structure where we organize data objects in a hierarchical order. A tree data structure consists of nodes. It is a recursive data structure. Each node has at most two children – the left child and the right child.

Basic Operations on Binary Tree

  • Inserting element
  • Deleting an element
  • Finding an element
  • Traversing

There are two ways to traverse a binary tree:

  • Depth-First Traversal
  • Breadth-First Traversal

Heap Data Structure

It is a special tree-based data structure in Java. It is a complete binary tree where we arrange all its nodes in a specific order. We use the heap to implement priority queues and find the k smallest or largest elements in an array.

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There are two types of heaps:

  • Max-Heap: The key at the root node should be the greatest among the key values of the children. The same property must be true for all sub-trees in the heap recursively.
  • Min-Heap: The key present at the root node should be minimum among the keys values of the children. The same property must be true for all sub-trees in the heap recursively.

Hash Table

Hash table data structures allow us to organize data based on some user-defined key structure. The hash table class implements a hash table that maps keys to values. We can use any non-null object as a value or a key.

In hashing, the large keys are transformed into small keys with hash functions. We store values in a data structure called a hash table. A hash table data structure implements a dictionary ADT which is a structure that can map unique keys to values.

Also Read: 100+ Java Interview Questions and Answers

Related Reads: Features of JAVA

What are algorithms in Java?

Algorithms help programmers to manipulate the data in the data structures. In Java, algorithms are static methods that we can use to perform different operations on collections. Various algorithms in Java to manipulate elements stored in data structures are:

  • Sorting Algorithms in Java
  • Searching Algorithms in Java

Sorting Algorithms in Java

Sorting algorithms arrange a given array or list elements in a certain order. The developers can arrange elements in a way that they are either in ascending or descending order. Sorting uses a comparison operator that decides the new order of the element in the respective data structure. Here are the most common sorting algorithms in Java:

Must Read: Data Types in Java – Primitive and Non-Primitive Data Types Explained

Merge Sort

Merge sort uses the divide and conquer strategy to sort the elements. The merge sort algorithm divides the input array into smaller segments till it obtains segments of only two elements or one element. Then, the elements in the smaller segments are sorted individually and the output segments are merged to produce the sorted array.

Merge Sort Algorithm

 
Merge Sort Algorithm
procedure MergeSort( a as array )
if ( n == 1 ) return a
var l1 as array = a[0] ... a[n/2]
var l2 as array = a[n/2+1] ... a[n]
l1 = mergesort( l1 )
l2 = mergesort( l2 )
return merge( l1, l2 )
end procedure
procedure merge( a as array, b as array )
var c as array
while ( a and b have elements )
if ( a[0] > b[0] )
add b[0] to the end of c
remove b[0] from b
else
add a[0] to the end of c
remove a[0] from a
end if
end while
while ( a has elements )
add a[0] to the end of c
remove a[0] from a
end while
while ( b has elements )
add b[0] to the end of c
remove b[0] from b
end while
return c
end procedure
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Must Explore: Merge Sort Algorithm (with code)

Quick Sort

Quicksort follows the divide and conquer algorithm. It divides the array into two halves, sorts each of them individually, and merges the sorted output to form a larger sorted array. The quick sort algorithm picks an element as a pivot and divides the given array around that pivot.

Quicksort Algorithm

 
QuickSort(A as array, low as int, high as int){
if (low < high){
pivot_location = Partition(A,low,high)
Quicksort(A,low, pivot_location)
Quicksort(A, pivot_location + 1, high)
}
}
Partition(A as array, low as int, high as int){
pivot = A[low]
left = low
for i = low + 1 to high{
if (A[i] < pivot) then{
swap(A[i], A[left + 1])
left = left + 1
}
}
swap(pivot,A[left])
return (left)}
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It is a simple sorting technique that repeatedly steps through the collection, compares each pair of adjacent elements, and swaps them if they are not in order.

Bubble Sort Algorithm

 
a[] is an array of size N
begin BubbleSort(a[])
declare integer i, j
for i = 0 to N - 1
for j = 0 to N - i - 1
if a[j] > a[j+1] then
swap a[j], a[j+1]
end if
end for
return a
end BubbleSort
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Must Check: Bubble Sort Algorithm in Java (with Code)

Searching Algorithms in Java

Developers use search algorithms to find an item from any data structure where it is stored. The two most common searching algorithms are:

Linear Search

The other name for the linear searching technique is sequential search. It is the simplest search algorithm that searches the items one by one. We can use it as an unsorted data set.

Linear Search Algorithm

linearSearch(array, size, key)

It will take a sorted array, start and end location as well as the search key as input. It will return the location of the key (if found) as the output.

For Example

Input

 
A list of data: 11 16 97 63 26 33 59 44
The search key: 33
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Output

Item found at location: 5

Must Read: Linear Search Algorithm (with code)

Binary Search

After sorting the list, we can binary search algorithm to find items on the list. A binary search algorithm divides the list into two sub-lists. If we find an item in the middle position, it returns the location. If t does not find the item in the middle, it jumps to either left or right sub-list to perform the same operation again until it finds the item or exceeds the range.

Binary Search Algorithm

binarySearch(array, start, end, key)

As input, it will take a sorted array, start and end location, and the search key. It will return the location of the key (if found) as the output.

For Example

Input

 
A sorted list of data: 10 21 35 47 53 67 78 81
The search key: 53
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Output

Item found at location: 4

Must Check: Binary Search Algorithm (with code)

Conclusion

That’s all about data structure and algorithms in Java. If you want to learn more data structures, you can take up an online Data Structure and Algorithm course in Java or any programming language of your choice.

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FAQs

Why data structures are important?

Data structures are the fundamental components of a computer program. They enable programmers to store and organize data so that it can be used efficiently. Data structures have applications in a variety of domains in computer science including operating systems and graphics.

How can I learn data structures and algorithms in Java?

One of the best ways to learn data structures and algorithms in Java is to take up online courses. Online courses can teach you the basics as well as advanced concepts related to DSA. Many platforms such as Coursera, Udemy, and edX offer comprehensive data structures and algorithms courses in different programming languages to help learners understand their implementation in the language of their choice.

How long will it take to learn data structures and algorithms in Java?

Depending on the time you dedicate to learning every week, the learning resource that you choose, it can take you around 6 weeks to 12 months to learn data structures and algorithms from scratch.

What are Data Structure in Java?

Ans. Data Structure are structured Programmed to store ordered data. In Java Data structure is broadly classified into Linear(Arrays, Linked List, Stack, Queues) and Hierarchical or Non-Linear (Binary Tree, Heap Data Structure and Hash Table) Data Structure.

What are the different types of algorithms in Java?

In Java, algorithms are static methods that are used to perform different operations on collection. Algorithms in Java are divided into two categories: Sorting Algorithm (Merge, Quick and Bubble) and Search Algorithm (Linear and Binary).

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