How do you alphabetize the order of Strings using Arrays.sort()?

Question

I'm working on review problems for an exam and one of the problems ask that I alphabetize book titles in order. I am asked to ignore the word "The", if it appears in the beginning of a title. My question is, is there a way to sort the title order of books while ignoring "The" using Arrays.sort()?

Originally I put the books in an Array list called books and then applied:

Arrays.sort(books);

It worked but only to some extent because it wouldn't ignore "The". Instead is it better to do:

public class booktest {

public static void main(String[] args) {
    System.out.println("Enter the title of your book: "); // The Great Gatsby
    String book = IO.readString();
    if(book.substring(0, 3).equalsIgnoreCase("the")){
        book = book.substring(4);
    }
    System.out.println(book); // Output: Great Gatsby

And then compare the first letters of each book to output the ascending order?

I was wondering if there was a simpler way to go about this. Any clues or suggestions would be appreciated. Thank you.

Answer 1

You have to be slightly careful.

1. book.substring(0, 3) throws a StringIndexOutOfBoundsException for strings of length less than 3.
2. A title that begins "the" does not necessarily begin with the word "The". It could begin with "There" for example.

If you are using Java 7 or an earlier version, I would make a separate method like this

private static String noThe(String b) {
    return b.length() >= 4 && b.substring(0, 4).equalsIgnoreCase("the ") ? b.substring(4) : b;
}

Then you can use

Arrays.sort(books, new Comparator<String>() {
    @Override
    public int compare(String b1, String b2) {
        return String.CASE_INSENSITIVE_ORDER.compare(noThe(b1), noThe(b2));
    }
});

In Java 8, you do not need a helper method as you can just do

Arrays.sort(books,
            Comparator.comparing(b -> b.length() >= 4 && b.substring(0, 4).equalsIgnoreCase("the ") ? b.substring(4) : b,
                    String.CASE_INSENSITIVE_ORDER));

Full example (Java 8 version):

String[] books = {
            "The Great Gatsby",
            "The Witches",
            "Persuasion",
            "It",
            "Therapy"};
Arrays.sort(books,
            Comparator.comparing(b -> b.length() >= 4 && b.substring(0, 4).equalsIgnoreCase("the ") ? b.substring(4) : b,
                    String.CASE_INSENSITIVE_ORDER));
System.out.println(Arrays.toString(books));

The output is

[The Great Gatsby, It, Persuasion, Therapy, The Witches]

Answer 2

You can pass a custom Comparator which does the trick. You can use any one based on the SDK.

Comparator using lambda expression

Comparator<String> c1 
        =  (String o1, String o2)->ignoreThe(o1).compareTo(ignoreThe(o2));

Comaprator for Java SDK v < 8

Comparator<String> java7Comparator = new Comparator<String>() {
    @Override
    public int compare(String o1, String o2) {
        return ignoreThe(o1).compareTo(ignoreThe(o2));
    }
};

Code Snippet

import java.util.ArrayList;
import java.util.Comparator;

public class BookComparison {
    public static void main(String[] args) {

        //Comparator using lambda expression
        Comparator<String> javaLambdaCompare 
            =  (String o1, String o2)->ignoreThe(o1).compareTo(ignoreThe(o2));

        //Comaprator for Java v < 7
        Comparator<String> java7Comparator = new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                return ignoreThe(o1).compareTo(ignoreThe(o2));
            }
        };

        ArrayList<String> books = new ArrayList<String>();
        //Add from source
        books.add("Robinson Crusoe by Daniel Defoe");
        books.add("Gulliver’s Travels by Jonathan Swift");
        books.add("David Copperfield by Charles Dickens");
        books.add("The Scarlet Letter by Nathaniel Hawthorne"); 
        books.add("The Moonstone by Wilkie Collins");
        books.add("Three Men in a Boat by Jerome K Jerome");

        //pass any of the Comparator as an argument to sort
        books.sort(javaLambdaCompare); 
    }
    public static String ignoreThe(String book){
        if(book.length()>=3 && book.substring(0, 3).equalsIgnoreCase("the")){
            book = book.substring(4);
        }
        return book;
    }
}

The result sorted list:

• David Copperfield by Charles Dickens,
• Gulliver's Travels by Jonathan Swift,
• The Moonstone by Wilkie Collins,
• Robinson Crusoe by Daniel Defoe,
• The Scarlet Letter by Nathaniel Hawthorne,
• Three Men in a Boat by Jerome K Jerome

Hope this helps!