How to create a Library Management System in Java using OOPs |

Introduction

This blog showcases a simplistic approach to library management system implementation using Object Oriented Programming (OOP). We will be creating a library management system with the following features :

Add a new book
Borrow a book
Return a book
Display all the books
Display available books

The source code of the project : github

Link of implementation : youtube

Prerequisites

Java JDK installed. link to install
VScode ( or any other IDE of your choice). link to install

Implementation

Start by creating a file named library.java.

Import the libraries

import java.util.HashMap;
import java.util.Scanner;

A hashmap is a data structure that pairs keys to values. In our case the keys are the book names and the value indicates the availability of the book.
- 0: indicating book is currently unavailable
- 1: book is available.
The Scanner class is used to get user input.

Create a Book class

class Book{
    String bookname;
    public Book(String name) {
        bookname= name;
    }  
}

The Book class has one attribute bookname and a constructor ( a special method that is used to initialize objects ).

Create a public class named library ( should match the name of your file )

The public keyword is used to declare that the class can be accessed by any other class in the same package or from any other package ( here package is the folder where your file is located ).

public class library {
}

We will be defining the main class and all the methods required for the library management system ( eg. addBook(), borrowBook()).

Initialize the HashMap

static HashMap<String, Integer> listOfBooks = new HashMap<String, Integer>();

The static keyword in Java is used to declare that the members ( variables and methods ) belong to the class rather than to instances of the class.

Since the list of books stays as it is irrespective of the instances we create, we use the static keyword for the listOfBooks.

Define required methods

addBook(): Adds a new book to the library

    public static void addBook(String bookname){
        listOfBooks.put(bookname,1);
        System.out.println("Book added!"); 
    }

The put method of hashmap adds the book with the book name and value 1.

displayAllBooks(): Displays all the books

    public static void displayAllBooks(){    
        for (String i : listOfBooks.keySet()) {
            System.out.println(i);
        } 
    }

The for loop iterates over the hashmap keys(bookname) and prints them all.

borrowBook() : Borrows a book

public static void borrowBook(String bookname){
        for (String i : listOfBooks.keySet()) {
            if(i.equals(bookname) && listOfBooks.get(i)==1){
                System.out.println("You can have the " +bookname + " book. Return after 5 days");
                listOfBooks.put(i, 0);
                return;
            }    
        }
        System.out.println("Sorry the book "+bookname+" is out of stock. Come back tomorrow!"); 
    }

The for loop iterates over the hashmap keys (bookname), finds the book, and checks for its availability. If the book is available (1), the book is borrowed and its availability is changed to unavailable (0).

returnBook(): Returns the borrowed book

public static void returnBook(String bookname) {
        if (listOfBooks.containsKey(bookname)) {
            if (listOfBooks.get(bookname) == 0) {
                listOfBooks.put(bookname, 1);
                System.out.println("Thank you for returning the book: " + bookname);
            } 
            else {
                System.out.println("This book is not currently borrowed.");
            }
        } 
        else {
            System.out.println("Sorry the book " + bookname + " doesn't exist.");
        }
    }

The method first checks if the book belongs to the library and its availability. Availability is made 1 indicating the book is available back.

displayAvailableBooks(): displays the available books

public static void displayAvailableBooks(){
    for (String i : listOfBooks.keySet()) {
            if(listOfBooks.get(i)==1){
                System.out.println(i);
            }    
        }
    }

These are the available books i.e. not borrowed by anyone.

Define the main class

    public static void main(String[] args) {}

In the main class, we will be taking inputs from the user and calling the required methods. But before that, declare the scanner class

    Scanner sc = new Scanner(System.in);

Now the last and final step:

      while(true){
        System.out.println("Choose your option");
        System.out.println("1.Add a book");
        System.out.println("2.Borrow a book");
        System.out.println("3.Return a book");
        System.out.println("4.Display all books");
        System.out.println("5.Display available books");
        System.out.println("6.exit");
        int option=sc.nextInt();
        sc.nextLine(); // Consume newline character
        switch (option) {
            case 1:
                System.out.println("Book name?");
                String bookname=sc.nextLine();
                if(bookname!=""){
                    addBook(bookname);
                }
                break;
            case 2:
            System.out.println("Book name?");
            String bookToBorrow=sc.nextLine();
                borrowBook(bookToBorrow);
                break;
            case 3:
            System.out.println("Book name?");
            String bookToReturn=sc.nextLine();
                returnBook(bookToReturn);
                break;
            case 4:
                displayAllBooks();
                break;
            case 5:
                displayAvailableBooks();
                break;
            case 6:
                System.out.println("Exiting from library management system!");
                return;

        }
    }

The options for performing actions like adding a book, borrowing a book, returning a book, etc are chosen using the Java switch case. The while loop keeps running until you choose to exit (case 6).

How to create a Library Management System in Java using OOPs