Exception in thread "main" java.lang.NullPointerException

Question

hi
I am new to Java, and taking an introductory course in java. I wrote the code given bellow and get following error "C:\java\assingment2>java test123
Exception in thread "main" java.lang.NullPointerException
at PartCatalog.Add(test123.java:56)
at test123.main(test123.java:102)"
Can any body help me please
import java.util.*;
class PartRecord
public String PartName;
public String PartNumber;
public float Cost;
public int Quantity;
public static int counter ;
public PartRecord()
{ PartName ="";
     PartNumber="";
Cost = 0;
     Quantity = 0;
     counter = 0;
public void Set(String name, final String num,
float cost, int quantity)
     PartName = name;
PartNumber= num;
Cost = cost;
Quantity = quantity;
counter++;
public float Get()
               return Cost*Quantity;
public static int Counter() {return counter;}
class PartCatalog
public PartCatalog()
npart=0;
public void Add(String name, String num,
float cost, int quantity)
if(npart>=1000) return;
Parts[npart++].Set(name,num,cost,quantity);
public float ShowInventory()
int inventory = 0;
for(int i=0; i<npart; i++)
inventory+= Parts.Get();
return inventory;
public PartRecord[] Parts = new PartRecord[1000];
public int npart;
class ExtPartCatalog extends PartCatalog
public void Sort()
Arrays.sort(Parts);
public void Print()
for(int i=0; i<npart; i++)
System.out.println ( Parts[i].PartName + "\t "
+ Parts[i].PartNumber + "\t "
+ Parts[i].Cost + "\t "
+ Parts[i].Quantity + "\n");
class test123{
public static void main(String args[])          
     ExtPartCatalog catalog = new ExtPartCatalog();
     catalog.Add("tire ", "1", 45, 200);
     catalog.Add("microwave", "2", 95, 10);
     catalog.Add("CD Player", "3", 215, 11);
     catalog.Add("Chair ", "4", 65, 10);
     catalog.Sort();
catalog.Print();
System.out.println("Inventory is " + catalog.ShowInventory());
ExtPartCatalog catalog2 = new ExtPartCatalog();
catalog2.Add("ttt ", "1", 45, 200);
System.out.print("\n\nTotally there are " + PartRecord.Counter() );
System.out.println(" Parts being set" );

Answer 1

Thank you for your reply. I think i used
public PartRecord[] Parts = new PartRecord[1000];
so i have created the reference. I tries what you told me but it still did not work. I am putting the code again, but now in the formatted form so that you can read it more easily. I will appreciate your help. Thanks
<code>
import java.util.*;
class PartRecord
{      public String PartName;
public String PartNumber;
public float Cost;
public int Quantity;
public static int counter ;
     public PartRecord()
          PartName ="";
          PartNumber="";
          Cost = 0;
          Quantity = 0;
          //counter = 0;
     public void Set(String name, final String num,
float cost, int quantity)
     PartName = name;
     PartNumber= num;
     Cost = cost;
     Quantity = quantity;
     counter++;
     public float Get()
     return Cost*Quantity;
     public static int Counter() {return counter;}
class PartCatalog
{      public PartRecord[] Parts = new PartRecord[1000];
     public int npart;
public PartCatalog()
npart=0;
     public void Add(String name, String num,
     float cost, int quantity)
     if(npart>=1000) return;
     Parts[npart++].Set(name,num,cost,quantity);
     public float ShowInventory()
          float inventory = 0;
          for(int i=0; i<npart; i++)
          inventory= Parts[npart].Get();
          return inventory;
/*class ExtPartCatalog extends PartCatalog
     public void Sort()
     Arrays.sort(Parts);
     public void Print()
               for(int i=0; i<npart; i++)
               System.out.println ( Parts.PartName + "\t "
                              + Parts[i].PartNumber + "\t "
                              + Parts[i].Cost + "\t "
                         + Parts[i].Quantity + "\n");
class azimi_a{
public static void main(String args[])
PartCatalog c = new PartCatalog() ;//= new PartCatalog[4];
c.Add("tire ", "1", 45, 200);
c.Add("microwave", "2", 95, 10);
c.Add("CD Player", "3", 215, 11);
c.Add("Chair ", "4", 65, 10);
<code>