Java Sorting: sort an array of objects by property, object not allowed to use Comparable

Question

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

Answer 1

Expanding @PeterLawrey's answer to Java 8, you can now use a Lambda Expression instead of a Comparable delegate:

Collections.sort(books, (firstBook, secondBook -> b1 is greater return +1, 
                                                  if b2 is smaller return -1 otherwise 0));