Having Trouble Referencing a Method from Anonther Method in Another Class

[Toshiro Hitsuguya]

Hi,

I am currently having trouble with a project I am working on. It is to create a simple system for a library.

Here is my code for the library class:

public class Library  {
	
	public boolean borrowbook() {
//trying to reference this in the Book class I have to do borrowBook.objectname. So it will return book as being borrowed.
		return Book.borrowed();
	}

	public boolean returnBook() { //same as above but for returned() method
		return Book.returned();
	}
}    

This is the class I am trying to refer to:

public class Book {
private String title;
private boolean borrowed; 
 
public Book(String bookTitle){ // Creates a new Book
	title = bookTitle; 
}
 
public boolean borrowed() { // Marks the book as borrowed. this is also one of the methods that I am trying to refer to.
	borrowed = true;
	return borrowed;
}
 
// Marks the book as available, i.e., not borrowed
public boolean returned() { //this is one of the methods that I am trying to refer to
	borrowed = false;
	return borrowed;
}
 
// Returns true if the book is borrowed, false otherwise
public boolean isBorrowed() {
	return borrowed; 
		
	
}
 
// Returns the title of the book
public String getTitle() {
return title; //once the a value has been created in Book(string bookTitle) it returns that value
	}
 
 
public static void main(String[] arguments){
// Small test of the Book class
Book example = new Book("The Da Vinci Code"); //This creates a new value in the bookTitle constructor 
System.out.println("Title (should be The Da Vinci Code): " + example.getTitle());
System.out.println("Borrowed? (should be false): " + example.isBorrowed());
example.borrowed();
System.out.println("Borrowed? (should be true): " + example.isBorrowed());
example.returned();
System.out.println("Borrowed? (should be false): " + example.isBorrowed());
	}
}    

With all of that. I have compiled Book.java fine. However, whenever I try to compile Library, I get a "non-static method can be referred from a static context". The library methods are not static.

My question is how can I rearrange the code in my library class to reference borrowed() and returned() in my book class?

[Ernest Friedman-Hill]

When you borrow a book from the library or return a book to the library, it's an action you perform relative to a specific book; it makes no sense to return a book without referring to a specific book, right? The Library doesn't know which book you're returning or borrowing, which leaves it up to you, the borrower -- the person who calls the methods. So I think the methods of Library need to accept the book as a parameter:

public class Library  {
	
	public boolean borrowbook(Book aBook) {
		return aBook.borrowed();
	}

	public boolean returnBook(Book aBook) {
		return aBook.returned();
	}
}    

[Toshiro Hitsuguya]

The reason I need to do this is because later I have to evoke the method in a format like this firstLibrary.borrowBook("The Lord of the Rings").

[Toshiro Hitsuguya]

Thanks for the information. I tried that and I am still getting "a non-static method cannot be referenced from a static context" error message. Also, how would I write those method if I have evoke the method for multiple books?

Thank you.

[Henry Wong]

I thought about continuing EFH analogy about how you need an instance of library to borrow a book -- hence, you won't know where to borrow it from. etc. But...

Unless, you have an understanding of static and non-static context, and what is in scope during what context, you will keep get these error messages. So... I recommend that you go back and review the chapter on methods. You need to review the difference between static and non-static methods, and how, when do you use them.

Henry