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    <p>If you can use <code>Comparators</code>, write one for each type of sorting you need, e.g., ascending for book title and descending for page number. The <code>compare</code> method of a <code>Comparator</code> must return positive if the first argument is larger than the second, negative if the first is smaller and zero if they are equal.</p> <pre><code>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&lt;Book&gt; ascTitle; static private Comparator&lt;Book&gt; descPageNumber; // We initialize static variables inside a static block. static { ascTitle = new Comparator&lt;Book&gt;(){ @Override public int compare(Book b1, Book b2){ return b1.getTitle().compareTo(b2.getTitle()); } }; descPageNumber = new Comparator&lt;Book&gt;(){ @Override public int compare(Book b1, Book b2){ // Java 7 has an Integer#compare function return Integer.compare(b1.getPageNumber(), b2.getPageNumber()); // For Java &lt; 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; public Book[] getBooks(){ return books; } public void sortAscTitle(){ Arrays.sort(books, ascTitle); } public void sortDescPageNumber(){ Arrays.sort(books, descPageNumber); } public Library(Book[] books){ this.books = books; } public static void main(String[] args){ Library library = new Library( new Book[]{ new Book("1984", 123), new Book("I, Robot", 152), new Book("Harry Potter and the Philosopher's Stone", 267), new Book("Harry Potter and the Goblet of Fire", 759), new Book("The Bible", 1623) }); library.sortAscTitle(); System.out.println(Arrays.toString(library.getBooks())); library.sortDescPageNumber(); System.out.println(Arrays.toString(library.getBooks())); } } </code></pre>
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    1. POJava Sorting: sort an array of objects by property, object not allowed to use Comparable
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    1. COThanks! Really nice! I was using Peter's suggestion for it, and that style of implementation jives a bit better in my class, however, this is really great too, and I was having trouble with the returns on it, so seeing that code really helped me a lot! Thanks so much! Ill be coming back to this question for reference every time I need to sort anything!
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