import java.io.File;
import java.io.IOException;
import java.util.Scanner;
public class ReadCellPhones {
public static void main(String Args[]) throws IOException {
Scanner s = new Scanner(System.in);
File Input = new File("Cellphone.txt");
Scanner f = new Scanner(Input);
String[] Cells = new String[20];
Double[] Amounts = new Double[20];
Double threshold = printmenu();
int number = 0;
while (f.hasNext()) {
Cells[number] = f.next();
Amounts[number] = f.nextDouble();
number++;
}
System.out.println("NUMBER\tArmount");
for (int i = 0; i < Amounts.length; i++) {
if (Amounts[i] > threshold)// THIS IS WHERE THE NULLPOINTER
// EXCEPTION OCCURS
{
System.out.print(Cells[i] + "\t" + Amounts[i]);
}
}
}
static Double printmenu() {
Scanner s = new Scanner(System.in);
System.out.print("Enter the filename: ");
String Filename = s.nextLine();
System.out.print("Cell Bill Threshold: ");
Double threshold = s.nextDouble();
return threshold;
}
}
所以我想做的是从文件中读取数据,将数据存储在两个数组中,如果 Amounts 数组值大于为阈值变量输入的值,则打印出数组。但是当我尝试运行该程序时,会弹出空指针错误,知道为什么吗?
最佳答案
问题是您读入的记录少于 20 条。
Amounts 数组中的每个 Double 默认值为 null。当 java 进行拆箱以便将 Amounts[i]
与 threshold
进行比较时,它会尝试取消引用该空值,从而创建异常。
解决方案是标记有多少个值被成功读入,并且只将这些值与阈值进行比较。
关于java.lang.nullpointerException?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13694472/