Answer: 

Book.java

public class Book {


	private int isbnno;


	private String bookName;


	private String author;


	public int getIsbnno() {


		return isbnno;


	}


	public void setIsbnno(int isbnno) {


		this.isbnno = isbnno;


	}


	public String getBookName() {


		return bookName;


	}


	public void setBookName(String bookName) {


		this.bookName = bookName;


	}


	public String getAuthor() {


		return author;


	}


	public void setAuthor(String author) {


		this.author = author;


	}


	@Override
	public String toString() {
		return "Book [isbnno=" + isbnno + ", bookName=" + bookName + ", author=" + author + "]";
	}


	
}

Library.java

import java.util.ArrayList;


public class Library {
	private ArrayList<Book> bookList = new ArrayList<Book>();


	public void addBook(Book bobj) {
		bookList.add(bobj);
	}


	public boolean isEmpty() {
		if (bookList.size() == 0) {
			return true;
		} else {
			return false;
		}
	}


	public ArrayList<Book> viewAllBooks() {
		return bookList;
	}


	public ArrayList<Book> viewBooksByAuthor(String author) {
		ArrayList<Book> booksByAuthor = new ArrayList<>();
		for (int i = 0; i < bookList.size(); i++) {
			if (bookList.get(i).getAuthor().equalsIgnoreCase(author)) {
				booksByAuthor.add(bookList.get(i));
			}
		}
		return booksByAuthor;
	}


	public int countnoofbook(String bname) {
		int count = 0;
		for (int i = 0; i < bookList.size(); i++) {
			if (bookList.get(i).getBookName().equalsIgnoreCase(bname)) {
				count++;
			}
		}
		return count;
	}


}

Main.java

import java.util.ArrayList;
import java.util.Scanner;


public class Main {


	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		Library library = new Library();
		while(true)
		{
			System.out.println("1.Add Book");
			System.out.println("2.Display all book details");
			System.out.println("3.Search Book by author ");
			System.out.println("4.Count number of books - by book name");
			System.out.println("5.Exit");
			System.out.println("Enter your choice:");
			int choice = Integer.parseInt(sc.nextLine());
			if(choice == 1)
			{
				System.out.println("Enter the isbn no:");
				int isbn = Integer.parseInt(sc.nextLine());
				System.out.println("Enter the book name:");
				String bname = sc.nextLine();
				System.out.println("Enter the author name:");
				String author = sc.nextLine();
				Book book = new Book();
				book.setAuthor(author);
				book.setBookName(bname);
				book.setIsbnno(isbn);
				library.addBook(book);
			}
			else if(choice == 2)
			{
				if(library.isEmpty())
				{
					System.out.println("Library is empty");
				}
				else
				{
					ArrayList<Book> bookList = library.viewAllBooks();
					for(Book b: bookList)
					{
						System.out.println(b);
					}
				}
			}
			else if(choice == 3)
			{
				System.out.println("Enter the author name:");
				String author = sc.nextLine();
				ArrayList<Book> bookByAuthor = library.viewBooksByAuthor(author);
				if(bookByAuthor.size() == 0)
				{
					System.out.println("None of the book published by the author Henry");
				}
				else
				{
					for(Book b: bookByAuthor)
					{
						System.out.println(b);
					}
				}
			}
			else if(choice == 4)
			{
				System.out.println("Enter the book name:");
				String bname = sc.nextLine();
				int count = library.countnoofbook(bname);
				System.out.println("Number of the books by the name "+bname+" are : "+count);
			}
			else if(choice == 5)
			{
				break;
			}
			else
			{
				System.out.println("Invalid choice, please try again");
			}
		}


	}


}

Step-by-step explanation

Please find the above code for all three required classes.