Java While-Loop問題

Question

我正在嘗試讀取包含此內容的.txt文件

lollipops 10 0.50 5.00 
dietsoda 3 1.25 3.75
chocolatebar 20 0.75 15.00

它的作用是在名稱，數量，價格，總計中添加四列，並從txt文件中讀取它們。 然后計算小計，營業稅，然后總計。 我不確定如何計算小計，因為總和始終是最后一個值，在這種情況下，這是巧克力棒的總和。

    import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Scanner;

public class CatalogTester
{
    public static double SALESTAX = 0.0625;

    public static void main(String[] args) throws FileNotFoundException
    {


        String name ="";
        int quantity = 0;
        double price =0;
        double total = 0;
        double subtotal = 0;
        double tax = 0;
        double total_all = 0;

        File inFile = new File("Catalog.txt");
        Scanner in = new Scanner(inFile);
        System.out.printf("%-30s %-10s %-10s %-10s\n", "Item", "Quantity","Price", "Total");
        System.out.println();
        System.out.println("Expected:Item                           Quantity   Price      Total");
        while(in.hasNext()){
            name = in.next();
            quantity = in.nextInt();
            price = in.nextDouble();
            total = in.nextDouble();
            System.out.printf("%-30s %-10d %-10.2f %-10.2f\n", name, quantity, price, total);
        }
        in.close();
        tax = subtotal * SALESTAX;
        total_all = subtotal+tax;


        System.out.println("Expected:lollipops                      10         0.50       5.00");
        System.out.printf("%-52s %-10.2f\n", "SubTotal", subtotal);
        System.out.println("Expected:SubTotal                                             23.75");
        System.out.printf("%-52s %-10.2f\n", SALESTAX * 100 + "% Sales Tax",tax);
        System.out.println("Expected:6.25% Sales Tax                                      1.48");
        System.out.printf("%-52s %-10.2f\n", "Total", total_all);
        System.out.println("Expected:Total                                                25.23");    
    }
}

Answer 1

您永遠不會重新分配line 。 因此，每次都檢查同一行。

String line = in.nextLine();
while(in.hasNextLine()){
   int i = 0;
   while(!Character.isDigit(line.charAt(i))) {i++;} //<--- same line

要解決此問題：

String line = in.nextLine();
    while(in.hasNextLine()){
       int i = 0;
       while(!Character.isDigit(line.charAt(i))) {i++;}
      //code
       line = in.nextLine(); //added
     }

Answer 2

您不會在while循環中讀取任何行...

您可能錯過了說：

line = in.nextLine();

在循環的盡頭。

Answer 3

在while條件下移動線路分配。

      String line = in.nextLine();
         while(in.hasNextLine()){

改成

      while(in.hasNextLine()){
         String line = in.nextLine();