Null Pointer Exception

[no1zson]

Can someone look at this with a new set of eyes and see what I am missing.
I am new to Java and this is kicking my tail.
This is a simple inventory application. I am using an array to store the variables in the Compactdisk class, and sort on the name when done.
I implimented a sub class to that named CdwArtist class since I had never done it before. (I wanted to see inheritance in action)
I have my array now using the CdwAction class like I should, everything compiles fine, but when I run it I get a NullPointerException when I enter STOP and exit my loop.
It looks to me as if I am missing something with my array, possibly crossing the name and the artist somehow, but I have stared at this so long it is just looking like garbage to me. Any help would be welcome.
Inventory class

import java.util.*;
 
public class Inventory 
{// begin class Inventory
 
 public static int maxlength = 0;
  public static CdwArtist[] sort(CdwArtist[] cds)
   { 
    Arrays.sort(cds, 0, maxlength); 
    return cds;
    }
 
 public static String toString(CdwArtist[] cds)
  { 
      String toSend = "\n\n"; 
 
    for(int i = 0; i < maxlength; i ++)
    toSend = toSend + cds[i].getName() + "\n";
    return toSend;
  } 
 
  public static void main(String[] args)
  {//begin method main
 
   // create cd Array 
    CdwArtist[] cds = new CdwArtist[100];
 
 
    float totalValue = 0; 
 
    Scanner input = new Scanner(System.in); // create scanner 
 
    // begin display method 
    System.out.print("Enter up to 99 CD Names or STOP to Exit: "); 
    String nameInput = input.nextLine(); //read cd name 
 
    maxlength ++; 
 
     for(int i = 1; i < cds.length && !nameInput.equalsIgnoreCase("STOP"); i++)
     {// begin main While
      cds[i] = new CdwArtist();
      cds[i].setName(nameInput);
 
      System.out.print("Enter CD Artist Name: "); // prompt for artist name
      CdwArtist artist = new CdwArtist(input.nextLine()); 
 
      System.out.print("Enter Price of this CD: "); // prompt for price
      cds[i].setPrice(input.nextFloat()); // price input from user. 
      while (cds[i].getPrice()<= 0) 
         {// begin while 
           System.out.print("Price Must Be Greater Than Zero. Enter Price: ");
            cds[i].setPrice(input.nextFloat()); // cd price loop from user.
          } // End while 
 
      System.out.print("Enter CD Item Number: "); // prompt for cd item number
      cds[i].setItemno(input.nextInt()); // cds item number input from user 
 
      System.out.print("Enter Number of these CDs in Stock: "); // prompt for cd stock 
      cds[i].setNstock(input.nextInt()); // cds in stock input from user
 
      System.out.print("\n\nCD "+cds[i].getName()+", Item Number "+cds[i].getItemno()+","); // display name 
      System.out.printf(" is worth %c%.2f.",'$', + cds[i].getPrice());//
      System.out.print("\nWe have "+ cds[i].getNstock()+" copies in stock,");
      System.out.printf(" making our inventory for this cd worth %c%.2f.\n", '$', + cds[i].getValue()); //inventory value 
 
      if(cds[i].getValue() != -1) totalValue = totalValue + cds[i].getValue();
      System.out.printf("Combined Inventory for all CDs is Worth %c%.2f.\n\n\n", '$', + totalValue);
 
      System.out.print("Enter up to 99 CD Names or STOP to Exit: "); 
      input=new Scanner(System.in); // internal loop prompt 
      nameInput = input.nextLine(); //name input from user 
 
      maxlength ++; 
      } // End main While
 
       //System.out.println(toString(cds));
        System.out.println(toString(sort(cds))); 
        System.out.print("Ending Program."); 
 
   }// end method main 
} // end class Payroll
 

then the compactdisk class I first set up (even though this should require no modification at all to impliment a subclass.

import java.lang.Comparable;
 
public class Compactdisk implements Comparable
{// begin class
 
    //InventoryCD class has 5 fields
    private String name; //  Name of cd
    private float price; // price of cd
    private int itemno; // item number of cd
    private int nstock; // how many units in stock    
    private int i; // cd counter for array
    private float value; // value for single cd inventory
 
 
    //Compact disk class constructor
    public Compactdisk()
 
        // 4 fields need to be set up
        { 
        name = "";
        price = 0;
        itemno = 0;
        nstock = 0;
        i = 0;
        value = 0;
        }
 
        // set values
       public void setName(String diskName)
       {
       name = diskName;
       }
        public void setPrice(float cdPrice)
       {
       price = cdPrice;
       }
        public void setItemno(int cdItemno)
       {
       itemno = cdItemno;
       }
         public void setNstock(int cdStock)
       {
       nstock = cdStock;
       }
        public void setValue(float cdValue)
        {
        value = cdValue;
        }
        public void seti(int Count)
        {
        i = Count;
        }
 
 
       // return values
        public String getName()
        {    
        return (name);
        }
        public float getPrice()
        {    
        return (price);
        }
        public int getItemno()
        {    
        return (itemno);
        }
        public int getNstock()
        {    
        return (nstock);
        }
        public int compareTo(Object in)
       {
       return ((Comparable)name.toLowerCase()).compareTo((Comparable)((Compactdisk)in).getName().toLowerCase());
       }
 
        // returns indivudual inventory value for a disk
       public float getValue()
       {
       return(price * nstock);
       }
 
 
 
 
 
}// end class
 

and then my new subclass. everything worked fine before I did this.

import java.util.*;
 
public class CdwArtist extends Compactdisk
{
 
    // CdwArtist class adds one field 
  public String artist; // artist performing on cd
 
 // Artist constructor
  public CdwArtist()
  {
  artist = "";
  }
 
    public CdwArtist(String in)
    {
    artist=in;
    }
 
    // get value
    public void setArtist(String in)
    {
    artist=in;
    }
 
    // return value
    public String getArtist()
    {
    return (artist);
    }
 
} //End Class

Anyone?

[ruch095]

your Inventory class in line 77 is cause of this Exception *-*
because if you enter string "Stop" for loop in line 39 is over and line 77 will be execute but on this step method toString is call but in for loop of this method
cds[i] (when you enter "Stop" the last element of this array doesn't create ) call getName() although it element haven't instant of CdwArtist. this cause make NullPointerException

sorry about my english T-T . i'm afraid you don't understand that i explain, on this link i uploaded every class that i resolve it (little code) for ignore this exception :)

http://www.mediafire.com/?6wdlhknndxd

[no1zson]

Actually, the problem was with my array. Line 39.

for(int i = 1; i < cds.length && !nameInput.equalsIgnoreCase("STOP"); i++)

needed to be changed to

for(int i = 0; i < cds.length && !nameInput.equalsIgnoreCase("STOP"); i++)

thanks anyways though. I appreciate the effort.