Trouble w/ Bubble Sort

[bri1547]

I am writing an inventory program that uses an array of objects. I need to bubble sort the array based on the product name then display the results. When I added the bubble sort I got a NullPointerException error in run time. I also have to display the total value of all the inventory. I have tried everything I can find in my java book and just can't seem to get it. Can anyone point me in the right direction? Here is my code:

Code:

public class Product
{
   public String itemNumber; // declare variable for item number
   public String productName; // declare variable for product name
   public int stockUnits; // declare variable for number of units in stock
   public double unitPrice; // declare variable for unit price of each product

   // Four argument constructor
   public Product( String item, String name, int units, double price )
   {
      itemNumber = item;
      productName = name;
      stockUnits = units;
      unitPrice = price;
   } // End four argument constructor

   public void setItemNumber( String itemNumber ) // Set item number
   {
      this.itemNumber = itemNumber;
   } // end set item number

   public String getItemNumber() // return item number
   {
      return itemNumber;
   } // end return item number

   public void setProductName( String productName ) // set product name
   {
      this.productName = productName;
   } // end set product name

   public String getProductName() // return product name
   {
      return productName;
   } // end return product name

   public void setStockUnits( int stockUnits ) // set units in stock
   {
      this.stockUnits = stockUnits;
   } // end set units in stock

   public int getStockUnits() // return units in stock
   {
      return stockUnits;
   } // end return units in stock

   public void setUnitPrice( double unitPrice ) // set unit price
   {
      this.unitPrice = unitPrice;
   } // end set unit price

   public double getUnitPrice() // return unit price
   {
      return unitPrice;
   } // end return unit price

   public double getTotalValue() // calculate total value
   {
      return stockUnits * unitPrice;
   } // end method to calculate total value



} // end class product

public class InventoryPart2
{

   public static void main( String args[] ) // begin main method
   { 
      Product Inventory[] = new Product[100]; // array for 100 inventory items
      Inventory[0] = new Product( "001", "Phone Case", 25, 7.99 ); // product 1 data
      Inventory[1] = new Product( "002", "Dream Catcher", 75, 9.99 ); // product 2 data
      Inventory[2] = new Product( "003", "T-Shirt", 100, 19.99 ); // product 3 data
         
      int flag = 0;
      Product temp;

      while (flag == 0)
      {
         flag = 1;
         for( int x = 0; x < Inventory.length - 1; ++x)
         {
            if( Inventory[x].getProductName().compareTo( Inventory[x+1].getProductName() ) > 0 )
            {
               temp = Inventory[x];
               Inventory[x] = Inventory[x+1];
               Inventory[x+1] = temp;
               flag = 0;
            }
         }
      }  

      // Display product data
      System.out.println( "Item#      Item              In-Stock      Price      Total Value\n" );
      System.out.printf( "%s      ", Inventory[0].getItemNumber() );
      System.out.printf( "%s              ", Inventory[0].getProductName() );
      System.out.printf( "%d         ", Inventory[0].getStockUnits() );
      System.out.printf( "%.2f       ", Inventory[0].getUnitPrice() );
      System.out.printf( "%.2f\n", Inventory[0].getTotalValue() );

      System.out.printf( "%s   ", Inventory[1].getItemNumber() );
      System.out.printf( "%s             ", Inventory[1].getProductName() );
      System.out.printf( "%d         ", Inventory[1].getStockUnits() );
      System.out.printf( "%.2f       ", Inventory[1].getUnitPrice() );
      System.out.printf( "%.2f\n", Inventory[1].getTotalValue() );

      System.out.printf( "%s   ", Inventory[2].getItemNumber() );
      System.out.printf( "%s                  ", Inventory[2].getProductName() );
      System.out.printf( "%d        ", Inventory[2].getStockUnits() );
      System.out.printf( "%.2f      ", Inventory[2].getUnitPrice() );
      System.out.printf( "%.2f\n", Inventory[2].getTotalValue() );
   } // end method main

} // end class InventoryPart2

[Niveditha]

Hi,
You have not initialized the variable

Quote:

Product temp;

i feel it should be

Quote:

Product temp= new Product();

for which you have to add a default constructor in Product class with no arguments..

[Norm]

Where do you get the NPE? You MUST post the full text of error messages.
Look at the line number referenced in the error message and think how any of the objects referenced in that statement could be null.

Inventory is defined to hold 100 elements, but your code only shows that 3 have been filled. Your code expects all 100 to be filled. It they are not filled, they will be null.

[bri1547]

Norm, eventually the inventory will be controlled by user input. Will I need to set up a counter of some sort to define the length of the array? Also, when I try to print the inventory by calling the get methods from class product I get a compile time error "cannot find symbol." I took the lines straight from a textbook which does not expound on the lines used to print. Here is the code and error message:

Code:

public class InventoryPart2
{

   public static void main( String args[] ) // begin main method
   { 
      Product Inventory[] = new Product[3]; // array for 3 inventory items
      Inventory[0] = new Product( "001", "Phone Case", 25, 7.99 ); // product 1 data
      Inventory[1] = new Product( "002", "Dream Catcher", 75, 9.99 ); // product 2 data
      Inventory[2] = new Product( "003", "T-Shirt", 100, 19.99 ); // product 3 data
         
      int flag = 0;
      Product temp;

      while (flag == 0)
      {
         flag = 1;
         for( int x = 0; x < Inventory.length - 1; ++x)
         {
            if( Inventory[x].getProductName().compareTo( Inventory[x+1].getProductName() ) > 0 )
            {
               temp = Inventory[x];
               Inventory[x] = Inventory[x+1];
               Inventory[x+1] = temp;
               flag = 0;
            }
         }
      }  

      // Display product data
      System.out.println( "Item#      Item              In-Stock      Price      Total Value\n" );

      for ( int counter = 0; counter < Inventory.length; counter ++ )
         System.out.printf( "%s%3s%12d%8.2f%6.2f", Inventory[counter].getItemNumber(), 
                             Inventory[counter].getProductName, Inventory[counter].getStockUnits,
                             Inventory[counter].getUnitPrice, Inventory[counter].getTotalValue );
      
      
   } // end method main

} // end class InventoryPart2

public class Product
{
   public String itemNumber; // declare variable for item number
   public String productName; // declare variable for product name
   public int stockUnits; // declare variable for number of units in stock
   public double unitPrice; // declare variable for unit price of each product

   // Four argument constructor
   public Product( String item, String name, int units, double price )
   {
      itemNumber = item;
      productName = name;
      stockUnits = units;
      unitPrice = price;
   } // End four argument constructor

   public void setItemNumber( String itemNumber ) // Set item number
   {
      this.itemNumber = itemNumber;
   } // end set item number

   public String getItemNumber() // return item number
   {
      return itemNumber;
   } // end return item number

   public void setProductName( String productName ) // set product name
   {
      this.productName = productName;
   } // end set product name

   public String getProductName() // return product name
   {
      return productName;
   } // end return product name

   public void setStockUnits( int stockUnits ) // set units in stock
   {
      this.stockUnits = stockUnits;
   } // end set units in stock

   public int getStockUnits() // return units in stock
   {
      return stockUnits;
   } // end return units in stock

   public void setUnitPrice( double unitPrice ) // set unit price
   {
      this.unitPrice = unitPrice;
   } // end set unit price

   public double getUnitPrice() // return unit price
   {
      return unitPrice;
   } // end return unit price

   public double getTotalValue() // calculate total value
   {
      return stockUnits * unitPrice;
   } // end method to calculate total value



} // end class product

InventoryPart2.java:37: cannot find symbol
symbol  : variable getProductName
location: class Product
                             Inventory[counter].getProductName, Inventory[counte
r].getStockUnits,
                                               ^
InventoryPart2.java:37: cannot find symbol
symbol  : variable getStockUnits
location: class Product
                             Inventory[counter].getProductName, Inventory[counte
r].getStockUnits,

  ^
InventoryPart2.java:38: cannot find symbol
symbol  : variable getUnitPrice
location: class Product
                             Inventory[counter].getUnitPrice, Inventory[counter]
.getTotalValue );
                                               ^
InventoryPart2.java:38: cannot find symbol
symbol  : variable getTotalValue
location: class Product
                             Inventory[counter].getUnitPrice, Inventory[counter]
.getTotalValue );

^
4 errors

[bri1547]

Norm, I figure out my problem...I forgot the parentheses! Wow...dumb! Thanks for not being one of those uptight types who thinks everyone should make the same mistakes they did. I really appreciate your help. Especially since you don't give away the answer, you lead me to it and make me find it on my own. Your help is invaluable!