Suppose you are implementing the Comparable interface in a class representing a Book, where the ordering is based on the number of pages in the book. Write a compareTo method for this class. You may assume that in the Book class there is an instance variable called numPages and a method called getNumPages.

Following are the code to this question:

public class Book implements Comparable<Book> //defining a class that inherits the interface

{

int numPage; //defining integer variable numPage

int getNumPage()//defining a method getNumPage

{

return numPage; //use return keyword to return numPage value

}

int compareTo(Book b)//defining a method compareTo that uses Book instance b

{

   //using multiple conditions

if (getNumPage() > b.getNumPage())//defining if block that checks getNumPage method value is greater then instance of getNumPage  

{

return 1; //return value 1

}

else if (getNumPage() == b.getNumPage())//defining else if block that checks method and its instance value is euqal    

{

return 0;//return 0

}

else //defining else block

{

return -1;//return value -1

}

}

}

Explanation:

In the above-given code, a class book is defined, that inherits the interface that is "Comparable<Book>". Inside the class, an integer variable "numPage" and a method "getNumPages" is defined, that returns the "numPage" value.

In the next step, the "compareTo" method is declared, which uses an instance of the book and use the conditional statement.