sorting 2 class arrays based on a common class variable

Question

Is it possible to sort two class arrays that have a common string type variable alphabetically in java? I have a parent and child classes, each set as an array and I want to sort them alphabetically based on a variable that is in the parent class, like a title. I am fairly new to java and want to know if there anything that can accomplish this in java. Thanks in advance for the help.

import java.util.Scanner;
import java.lang.reflect.Array;
import java.text.NumberFormat;
import java.util.Locale;

//declaration of class Bookstore
public class Bookstore
{

// main method begins execution of program
public static void main (String [] agrs)
{

    //declare and set variables
    double price = 0.0;
    int year = 0;
    String isbn = "";
    String publisher = "";
    String author = "";
    String title = "";
    String website = "";
    double value = 0.0;
    double sum = 0;

// create Scanner to obtain user input
Scanner input = new Scanner(System.in);

//create a format for currency
NumberFormat nf = NumberFormat.getCurrencyInstance(Locale.US);


//construct the Book object as an array
Book[] bk = new Book[3];
EBook[] ebk = new EBook[2];

//for loop to distinguish between the Book array elements
for (int i = 0; i <bk.length; i++)
    bk[i] = new Book (title, price, year, publisher, author, isbn);

//for loop to distinguish between the EBook array elements
for (int i = 0; i <ebk.length; i++)
    ebk[i]= new EBook(isbn, price, year, publisher, author, title, website);

//set values for variables in the Book class array
bk[0].setIsbn("9780345917430");
bk[0].setTitle("Lord of the Rings");
bk[0].setAuthor("J. R. R. Tolkien");
bk[0].setYear(1954);
bk[0].setPublisher("Allen & Unwin");
bk[0].setPrice(10.75);

bk[1].setIsbn("0747532699");
bk[1].setTitle("Harry Potter");
bk[1].setAuthor("J. K. Rowling");
bk[1].setYear(1998);
bk[1].setPublisher("Scholastic Press");
bk[1].setPrice(14.12);


//calculate value of Book class
for (int i = 0; i <bk.length; i++)
    value += bk[i].getPrice();

//calculate value of Book class
for (int i = 0; i <ebk.length; i++)
    sum+= ebk[i].getPrice();

//calculate value of entire inventory
for (int i = 0; i <ebk.length; i++)
value = value + sum - ebk[i].getDiscount();

//display results
for (int i = 0; i <bk.length; i++)
    System.out.println(bk[i].toString());
for (int i = 0; i <ebk.length; i++)
    System.out.println(ebk[i].toString());

//display total value of inventory
System.out.println("Total inventory:    " + nf.format(value));
}
}


class Book
{

//define variables
private String isbn;
private double price;
private String publisher;
private String author;
private String title;
private int year;

//constructor that initializes fields
public Book(String title, double price, int year, String publisher, String author, String isbn)
{
    this.isbn = isbn;
    this.price = price;
    this.publisher = publisher;
    this.author = author;
    this.title = title;
    this.year = year;
}

//empty constructor
public Book()
{
    this("", 0.0, 0, "", "", "");
}

//set ISBN
public void setIsbn(String isbn)
{
    this.isbn = isbn;
}

//get ISBN
public String getIsbn() {
    return this.isbn;
}

//set price
public void setPrice(double price)
{
    this.price = price; 
}

//get price
public double getPrice()
{
    return this.price;
}

//set year
public void setYear(int year)
{
    this.year = year; 
}

//get year
public int getYear()
{
    return this.year;
}

//set publisher
public void setPublisher(String publisher)
{
    this.publisher = publisher; 
}

//get publisher
public String getPublisher()
{
    return this.publisher;
}

//set author
public void setAuthor(String author)
{
    this.author = author; 
}

//get author
public String getAuthor()
{
    return this.author;
}

//set title
public void setTitle(String title)
{
    this.title = title; 
}

//get title
public String getTitle()
{
    return this.title;
}

//display results
public String toString()
{

    //create a format for currency
    NumberFormat nf = NumberFormat.getCurrencyInstance(Locale.US);

    return "ISBM number:        " + this.isbn + "\n" +
            "Title:         " + this.title + "\n" +
            "Author's name:     " + this.author + "\n" +
            "Year published:        " + this.year + "\n" +
            "Publisher's name:  " + this.publisher + "\n" +
            "Sale price:        " + nf.format(this.price) + "\n" +
            "\n-----------------------------------------------------------------------\n";
}
}

class EBook extends Book
{
//define variable
private String website;

public EBook(String title, double price, int year, String publisher, String author, String isbn, String website)
{
    super(title, price, year, publisher, author, isbn);
    this.website = website;
}

//empty constructor
public EBook()
{
    this.website = "";
}

//get website
public String getWebsite()
{
    return website;
}

//set website
public void setWebsite(String website)
{
    this.website = website;
}

//set discount
public double getDiscount()
{
    return super.getPrice() * 0.10;
}

@Override
public String toString() {
    //create a format for currency
    NumberFormat nf = NumberFormat.getCurrencyInstance(Locale.US);

    return "ISBN number:        " + super.getIsbn() + "\n" +
            "Title:         "  + super.getTitle() + "\n" +
            "Author's name:     " + super.getAuthor() + "\n" +
            "Year published:        " + super.getYear() + "\n" +
            "Publisher's name:  " + super.getPublisher() + "\n" +
            "Sale price:        " + nf.format(super.getPrice()) + "\n" +
            "Website:       " + this.website + "\n" +
            "Discount:      " +nf.format(super.getPrice() * 0.10) + "\n" +
            "\n-----------------------------------------------------------------------\n";
}


}

Please check the answer I posted. If it helps let me know. If it works for you please mark it accept as answer. :) — vkg
– vkg, Commented May 3, 2014 at 3:16

vkg · Accepted Answer · 2014-05-03 03:35:25Z

3

Yes that is doable. Just try implementing Comparable interface for Base class that is Book class only.

class Book implements Comparable<Book> {
    // Your Rest of the code...

    // Rest of the code ...
    @Override
    public int compareTo(Book o) {
        if(o == null) {
            return 1;
        }
        if (this == o) {
            return 0;
        } else {
            if(this.title != null && o.title != null) {
                return this.title.compareTo(o.title);
            } else if(this.title != null) {
                return 1;
            } else {
                return -1;
            }
        }
    }
}

And to sort the array use

Arrays.sort(bk);

Hope it helps you :)

edited May 3, 2014 at 3:35

answered May 3, 2014 at 3:14

vkg

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7 Comments

Makoto Over a year ago

A null entity and a non-null entity are not equivalent. Otherwise your answer is correct.

vkg Over a year ago

Can you please explain? I am just proving a guideline. Not coding for someone. :) Hope you would agree with me.

Makoto Over a year ago

Certainly. If I have an instance of an object, and I'm comparing it against null, I'm comparing something that exists against something that doesn't exist. 0 in a compareTo represents object equivalence; that is, they compare equivalently. I firmly believe that comparing anything that exists against null should mean that it returns 1 instead of 0, as the non-null object is clearly greater than the null object.

vkg Over a year ago

With due respect to you IMHO it's not how it works. You can try a sample your self.

Makoto Over a year ago

Oh. You're not even checking for null. Whoops, my bad. You might want to check for null in your comparison, though.

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