Book.java

public class Book {
    static int totalNoOfBooks;
    String author;
    String title;
    String isbn;
    boolean isBorrowed;

    static {
        totalNoOfBooks=0;
    }
    {//object initialisation
        totalNoOfBooks++;
    }

    Book(String isbn,String title,String author){
        this.isbn =isbn;
        this.title =title;
        this.author = author;
    }
    Book(String isbn){
        this(isbn,"Unknown","Unknown");
    }

    static int getTotalNoOfBooks(){
        return totalNoOfBooks;
    }

    void borrowBook(){
        if(isBorrowed){
            System.out.println("Book is already Borrowed");
        }else {
            this.isBorrowed = true;
            System.out.println("Enjoy the book");
        }
    }
    void returnBook(){
        if(isBorrowed){
            this.isBorrowed=false;
            System.out.println("Hope you enjoyed, please leave a review");
        }else{
            System.out.println("This book is already in th library");
        }
    }

    public static void main(String[] args) {
        Book designOfThings=new Book("01","Design","Author");
        Book mybook =new Book("02");
        System.out.println(Book.getTotalNoOfBooks());
        designOfThings.borrowBook();
        mybook.borrowBook();
        designOfThings.borrowBook();
        designOfThings.returnBook();
    }

}