I have a class, Library, that contains an array of Book objects, and I need to sort the array based off the properties of Book, either Title or PageNumber. The problem is im not allowed to use the Comparable class with Book. How would you recommend I sort the array of Books in library? Write my own sort? Or is there an easier way? If you need snippets of code, just ask!
If you can use Comparators, write one for each type of sorting you need, e.g., ascending for book title and descending for page number. The compare method of a Comparator must return positive if the first argument is larger than the second, negative if the first is smaller and zero if they are equal.
import java.util.Comparator;
import java.util.List;
import java.util.Arrays;
class Book{
String title;
int pageNumber;
public Book(String title, int pageNumber){
this.title = title;
this.pageNumber = pageNumber;
}
String getTitle(){ return title; }
int getPageNumber(){ return pageNumber; }
public String toString(){
return "(" + title + ", " + pageNumber + " pages)";
}
}
public class Library{
// These variables are static because you don't need multiple copies
// for sorting, as they have no intrinsic state.
static private Comparator<Book> ascTitle;
static private Comparator<Book> descPageNumber;
// We initialize static variables inside a static block.
static {
ascTitle = new Comparator<Book>(){
@Override
public int compare(Book b1, Book b2){
return b1.getTitle().compareTo(b2.getTitle());
}
};
descPageNumber = new Comparator<Book>(){
@Override
public int compare(Book b1, Book b2){
// Java 7 has an Integer#compare function
return Integer.compare(b1.getPageNumber(), b2.getPageNumber());
// For Java < 7, use
// Integer.valueOf(n1).compareTo(n2);
// DO NOT subtract numbers to make a comparison such as n2 - n1.
// This can cause a negative overflow if the difference is larger
// than Integer.MAX_VALUE (e.g., n1 = 2^31 and n2 = -2^31)
}
};
}
private Book[] books;
p