How to make the array sort by Product[counter].getProductTitle() ?

Question

Question: Where does "productArray" come from in these:

for ( Product product : productArray )

&

Arrays.sort( productArray, new ProductComparator() );

Question: What am I doing wrong? How do I make this sort?

Related Post from Yesterday

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                                 EDIT

:::EDIT::: Ok I took your advice here about

Product productArray[] = new Product[ARRAY_LENGTH]

Now it is broke here

/tmp/jc_22339/InventoryPart2.java:99: cannot find symbol
symbol  : variable productArray
location: class InventoryPart2
    for ( Product product : productArray ) {
                            ^
/tmp/jc_22339/InventoryPart2.java:101: cannot find symbol
symbol  : variable productArray
location: class InventoryPart2
     inventoryValue += productArray.calcInventoryValue();
                       ^

And if I do it like

for ( Product product : productArray[] ) {

I get

/tmp/jc_23524/InventoryPart2.java:69: '.class' expected
 for ( Product product : productArray[] ) {
                                        ^

So I am back stuck.

---

Begin program

:::Updated Code:::

    /**
 This program stores a collection of a product and its variables in a java array
 It will sort and display the information with a total
 */

// Import statements go here
import java.util.Scanner;// Import and use scanner
import java.util.Arrays;


public class InventoryPart2 {

    /**
     * @param args the command line arguments
     */

    public static void main(String[] args) {// begin main

     // Define your array of product objects and index here
        final int ARRAY_LENGTH = 5;// declare constant 
        final int version = 2;// declare int version number   

     // Create instance of Scanner class
     Scanner input = new Scanner( System.in );// new Scanner for CL input
     // Set counter to loop x times to populate your array of product objects
     int counter = 0;

     // Initialize your product array with the number of objects to populate it with
     Product productArray[] = new Product[ARRAY_LENGTH];// create array Product of class Product 

        // Welcome message
        System.out.printf( "\n%s%d\n" , 
        "Welcome to the Productentory Program v.", version );

        // Construct default values for Product
        productArray[0] = new Product("EThe Invisible Man", 0, 8.50);
        productArray[1] = new Product("DThe Matrix", 1, 17.99);
        productArray[2] = new Product("CSe7en", 7, 12.99);
        productArray[3] = new Product("BOceans Eleven", 11, 9.99);
        productArray[4] = new Product("AHitch Hikers Guide to the Galaxy", 42, 18.69);

     /*// Loop as many times as your counter variable
     {

      // Instantiate a product object

      // Prompt for product name and call the set method on your product object

      // Prompt for item number and call the set method on your product object

      // Prompt for units in stock and call the set method on your product object

      // Prompt for unit price and call the set method on your product object

      // store product object in array element

      //Destroy product object reference
      product = null;

      // Flush the buffer
       input.nextLine();

     }*/

     // Sort product array by product name using Comparator implementation class
     sortProductArray();

     // Print sorted array
     for ( Product product : productArray[] ) {
     if ( counter == 0 )
      System.out.printf( "\n%s\n", "Sorted Inventory of DVD movies");
     System.out.printf( "\n\n%s%d\n%s%s\n%s%d\n%s%,.2f\n%s%,.2f\n",
     "Item Number:      ",counter,
     "DVD Title:        ",productArray[counter].getProductTitle(),
     "Copies in stock:  ",productArray[counter].getUnitsInStock(),
     "Price each disk:  $",productArray[counter].getUnitPrice(),
     "Value of disks:  $",productArray[counter].calcInventoryValue());//End print
     counter++; 
     if ( counter == productArray.length)// on last counter of loop print total
      System.out.printf( "\n%s%,.2f\n\n\n",
      "Collection Value: $",calcTotalInventoryValue());
     }

     // Calculate total Inventory value

    }


 // method to calculate the total Inventory value
 private static double calcTotalInventoryValue()
 {

    double inventoryValue = 0;

    // Iterate array of product objects and calculate total value of entire Inventory
    for ( Product product : productArray ) {
     // accumulate inventory value from each product object in array
     inventoryValue += productArray.calcInventoryValue();
    }

     return totalInventoryValue;

 } // end method calcInventoryValue


 // method to sort product array
 private static void sortProductArray()
 {

    Arrays.sort( productArray, new ProductComparator() );



 } // end method calcInventoryValue


}

Answer 1

This

Product Product[] = new Product[ARRAY_LENGTH];

should be this:

Product productArray[] = new Product[ARRAY_LENGTH];

-- Edit

You'll also need to change relevant lines referring to this 'variable'.

If I may suggest, if you're confused by this, you ask your teacher/book to refresh your memory on "variables".

And don't worry if you don't get it: keep asking until you do. You're cut out for it if you're interested enough to learn. So be interested, ask questions, do your own research, and life will be good.

Answer 2

I think "productArray" is supposed to refer to the array of products you've created. So on the line:

Product Product[] = new Product[ARRAY_LENGTH];// create array Product of class Product

Change it too:

Product[] productArray = new Product[ARRAY_LENGTH];

Answer 3

You either have to have an array of Product as a member of the InventoryPart2 class OR passed into the sortProductArray method. You'll have to change that method to return a reference to the sorted array if you choose the latter.

Your Product array is in the static main method and not part of the object, so you've got a problem. I'd recommend that you do something like this:

public class Inventory
{
    private static final int DEFAULT_INVENTORY_SIZE = 5;
    private Product [] products;
    private int numProducts;

    public Inventory()
    {
       this(DEFAULT_INVENTORY_SIZE);
    }

    public Inventory(int size)
    {
       products = new Product[size];
       numProducts = 0;
    }

    public void addProduct(Product p)
    {
       products[numProducts++] = p;

    }

    public void sort()
    {
        // sort the array here
    }

    public String toString()
    {
        StringBuilder builder = new StringBuilder(1024);

        // Create a string representation of you inventory here

        return builder.toString();
    } 
}

Object oriented programming is about encapsulation and information hiding. Write the class in such a way that clients don't have to know or care whether you're using an array or something else to hold onto Products. You're abstracting the idea of Inventory here.

UPDATE:

This is your code, only better and running:

import java.util.Scanner;
import java.util.Arrays;

public class InventoryPart2
{
   public static void main(String[] args)
   {
      final int ARRAY_LENGTH = 5;
      final int version = 2;

      int counter = 0;

      Product productArray[] = new Product[ARRAY_LENGTH];

      System.out.printf("\n%s%d\n",
      "Welcome to the Productentory Program v.", version);

      productArray[0] = new Product("EThe Invisible Man", 0, 8.50);
      productArray[1] = new Product("DThe Matrix", 1, 17.99);
      productArray[2] = new Product("CSe7en", 7, 12.99);
      productArray[3] = new Product("BOceans Eleven", 11, 9.99);
      productArray[4] = new Product("AHitch Hikers Guide to the Galaxy", 42, 18.69);

      productArray = sortProductArray(productArray);

      // Print sorted array
      for (Product product : productArray)
      {
         if (counter == 0)
         {
            System.out.printf("\n%s\n", "Sorted Inventory of DVD movies");
         }
         System.out.printf("\n\n%s%d\n%s%s\n%s%d\n%s%.2f\n%s%.2f\n",
         "Item Number:      ", counter,
         "DVD Title:        ", product.getProductTitle(),
         "Copies in stock:  ", product.getUnitsInStock(),
         "Price each disk:  $", product.getUnitPrice(),
         "Value of disks:  $", product.calcInventoryValue());
         counter++;
      }
      System.out.printf("\n%s%,.2f\n\n\n",
      "Collection Value: $", calcTotalInventoryValue(productArray));
   }

   private static double calcTotalInventoryValue(Product[] productArray)
   {
      double inventoryValue = 0;

      for (Product product : productArray)
      {
         inventoryValue += product.calcInventoryValue();
      }

      return inventoryValue;

   }

   private static Product[] sortProductArray(Product[] productArray)
   {
      Arrays.sort(productArray, new ProductComparator());

      return productArray;
   }
}

I removed those comments you add everywhere. They're just clutter; I'd recommend that you not do that anymore. Better to make your code more readable and self-documenting by using better variable and method names.

This still isn't the way I'd recommend that you write it, but it works. You're more likely to see why this works if I don't alter it too much.

UPDATE 2:

Just in case you're interested, here's how I might write it:

    import java.util.Scanner;
import java.util.Arrays;
import java.text.NumberFormat;

public class Inventory
{
   private static final int DEFAULT_LENGTH = 5;
   private static final int VERSION = 2;

   private Product[] products;
   private int numProducts;

   public static void main(String[] args)
   {
      Inventory inventory = new Inventory(5);

      inventory.addProduct(new Product("EThe Invisible Man", 0, 8.50));
      inventory.addProduct(new Product("DThe Matrix", 1, 17.99));
      inventory.addProduct(new Product("CSe7en", 7, 12.99));
      inventory.addProduct(new Product("BOceans Eleven", 11, 9.99));
      inventory.addProduct(new Product("AHitch Hikers Guide to the Galaxy", 42, 18.69));

      System.out.println(inventory);
      System.out.println("total value: " + NumberFormat.getCurrencyInstance().format(inventory.getTotalValue()));
   }

   public Inventory()
   {
      this(DEFAULT_LENGTH);
   }

   public Inventory(int size)
   {
      products = new Product[size];

      this.numProducts = 0;
   }

   public void addProduct(Product p)
   {
      products[numProducts++] = p;
   }

   public double getTotalValue()
   {
      double inventoryValue = 0.0;

      for (Product product : products)
      {
         inventoryValue += product.calcInventoryValue();
      }

      return inventoryValue;
   }

   public String toString()
   {
      StringBuilder builder = new StringBuilder(1024);
      String newline = System.getProperty("line.separator");

      if (products.length > 0)
      {
         Arrays.sort(products, new ProductComparator());
         for (Product product : products)
         {
            builder.append(product).append(newline);
         }
      }

      return builder.toString();
   }
}

Answer 4

Don't think to yourself that everyone here started out being able to spot syntax errors in a matter of seconds. We weren't born this way, we just know what to look for because we've made the exact same mistake hundreds of times.

So if you're convinced you want to be a programmer even when you're at your wits end because of stuff like this you are cut out for it. Dedication and passion are far more important than natural talent.

Keep your head up. We'll be here the next time you get stuck. :)