Storing data into Object Array Elements returns NullPointerException

Code :

import java.io.*;

class Customer
{
    String name;
    int ID;
    int purchasequantity;
    double purchaseprice;


    Customer()
    {
        name = "";
        ID = 0;
        purchasequantity = 0;
        purchaseprice = 0.0;
    }


}

class StoreSell
{
    public static void main(String args[]) throws IOException
    {
        Customer[] cst = new Customer[3];

        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(isr);

        double totalAmount = 0;

        System.out.println("Size of Array " + cst.length);

        for (int i=0;i<cst.length;i++)
        {
            System.out.println("Enter Customer Name : ");
            cst[i].name = br.readLine();
            cst[i].ID = 100 + (i+1);
            System.out.println("Customer ID Generated is : "+cst[i].ID);
            System.out.println("Enter Purchase Price per Piece : ");
            //String price = br.readLine();
            //System.out.println("Entered Price is " +price);
   开发者_JAVA技巧         cst[i].purchaseprice = Double.parseDouble(br.readLine());
            System.out.println("Enter Purchase Quantity : ");
            cst[i].purchasequantity = Integer.parseInt(br.readLine());
        }

        System.out.println(" Customer ID "  + "Customer Name " + "Price Per Piece " + "Quntity " + "Bill Amount ");

        for(int i=0;i<cst.length;i++)
        {
            System.out.print(cst[i].ID + " " +cst[i].name+" "+ cst[i].purchaseprice + " " + cst[i].purchasequantity);
            double tempAmount = StaticMethod.calculateStatic(cst[i].purchaseprice, cst[i].purchasequantity);
            totalAmount = totalAmount + tempAmount;
            System.out.println(" " + tempAmount);
        }

        System.out.println("Total Sell of the day : Amount : " + totalAmount);
    }

}

Output :

Size of Array 3
Enter Customer Name : 
Nirav
Exception in thread "main" java.lang.NullPointerException
    at StoreSell.main(StoreSell.java:38)

Explanation :

1. The said program doesn't throw any compilation error.
2. While running the program, when data is entered on console for Name, it is able to fetch the data from console, but not able to store into array object.
3. I have tried to store the data retrieved from Console into a temp variable (Not an array element), and it stores correctly.
4. Hence, I can conclude that the problem occurs only when it tries to store data into an array object.
5. However, array is created successfully. I have tried to print the array length. and it gives correct length.. 3.

Please help me on this, I have tried to google lot on it, but not able to find any fix for the same.

Customer[] cst = new Customer[3];

This creates the array, not the individual elements, you need to create those yourself, e.g. in the loop:

for (int i=0;i<cst.length;i++)
{
    cst[i] = new Customer();

Initialising an array populates all positions within the array with the default value, and for an array of objects the default value is null. So the following code:

Customer[] cst = new Customer[3];

creates the following array:

{null, null, null}

There are numerous ways of initialising arrays, but if you're definately only going to be using a 3 element array just go for this one:

Customer cst[] = {new Customer(), new Customer(), new Customer()};

This is a guess* Call me crazy but does this, cst[i].ID = 100 + (i+1); actually increment i?