将数据存储到对象数组元素返回NullPointerException异常 [英] Storing data into Object Array Elements returns NullPointerException

问题描述

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);
            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);
    }

}

输出：

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

说明：

1. 上述程序不抛出任何编译错误。


2. 当运行程序，当控制台名称输入数据时，它能够从控制台读取数据，但无法存入数组对象。


3. 我试图存储从控制台检索到一个临时变量（非数组）中的数据，并正确储存。


4. 因此，我可以断定，只有当它试图将数据存储到一个数组对象出现问题。


5. 然而，阵列创建成功。我试图打印数组的长度。并给出了正确的长度。3。

请帮我在这，我试图谷歌很多的钱，但没能找到相同的任何修补程序。

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

推荐答案

正在初始化数组填充用默认值在阵列内所有的位置，并为对象的数组的默认值为null。所以下面code：

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];

创建以下数组：

{null, null, null}

有初始化数组的多种方式，但如果你只肯定将要使用3元素数组只是去为这一个：

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()};

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