sorting by a primitive int field

[saima kanwal]

I am trying to sort my array list using comparator. please review my code and solve my problem. I want to sort my array list by int type isbn number of book. My code is as follows:

import java.util.*;
 class TitleSort implements Comparator<Book> { 
	public int compare(Book b1, Book b2) { 
	 return b1.title.compareTo(b2.title);
	}
 }

 class IsbnSort implements Comparator<Book> { 
	public int compare(Book b1, Book b2) { 
	 return b1.isbn.compareTo(b2.isbn);
	}
 }

class Book { 
	String title;
	String author;
	int isbn;
	
 public Book(String t,String a, int i) { 
	title = t;
	author = a;
	isbn = i;
	}
 public String toString() { 
	String s1 = "title:" + title + " author:" + author + " isbn #:" + isbn + "\n";
	return s1;
	}

 
}
	
	

public class check1{
	public static void main(String[] args) { 
	Book b1 = new Book("Scjp","Kathy Sierra",1545);
	Book b2 = new Book("David Copperfield", "Charles Dickens", 6460);
	Book b3 = new Book("Sense & Sensibility", "Jane Austin", 1233);
	ArrayList<Book> books = new ArrayList<Book>();
	books.add(b1);
	books.add(b2);
	books.add(b3);
	System.out.println(books);
	TitleSort ts = new TitleSort();
	Collections.sort(books,ts);
	System.out.println(books);
	IsbnSort is = new IsbnSort();
	Collections.sort(books,is);
	System.out.println(books);
	} 

And it does not compile because I am using the compare to method with int. How am i going to compare int (primitive)? please modify my code.

saima.

[Christophe Verré]

Hint: The Integer class is comparable

[Ankit Garg]

return b1.isbn.compareTo(b2.isbn);

In the above statement, isbn is a primitive so you can't call compareTo method on it. But since it is a primitive, you can use comparison operator on it. So if you see the source code of Integer class, the compareTo method is implemented like this

public int compareTo(Integer anotherInteger) {
     int thisVal = this.value;
     int anotherVal = anotherInteger.value;
     return (thisVal<anotherVal ? -1 : (thisVal==anotherVal ? 0 : 1));
}

You can implement your compareTo method in the same way too. To make it even simpler, you can just write

return b1.isbn - b2.isbn;