java - 尝试并发现问题

Question

我试图在这个例子中编写一个“try and catch”方法，但由于某种原因，我在所有变量上都出错了: “找不到标志”。在以下所有情况下都会发生这种情况:小计&客户类型。有谁知道这是什么原因造成的？

import java.text.NumberFormat;
import java.util.Scanner;
import java.util.*;

public class InvoiceApp
{
public static void main(String[] args)
{
    Scanner sc = new Scanner(System.in);
    String choice = "y";

    while (!choice.equalsIgnoreCase("n"))
    {
        // get the input from the user
        try
        {    
        //System.out.print("Enter customer type (r/c): ");
            String customerType = getValidCustomerType(sc);
            System.out.print("Enter subtotal:   ");
            double subtotal = sc.nextDouble();
        }
        catch (InputMismatchException e)
        {
            sc.next();
            System.out.println("Error! Invalid number. Try again \n");
            continue;
        }

        // get the discount percent
        double discountPercent = 0;
        if (customerType.equalsIgnoreCase("R"))
        {
            if (subtotal < 100)
                discountPercent = 0;
            else if (subtotal >= 100 && subtotal < 250)
                discountPercent = .1;
            else if (subtotal >= 250)
                discountPercent = .2;
        }
        else if (customerType.equalsIgnoreCase("C"))
        {
            if (subtotal < 250)
                discountPercent = .2;
            else
                discountPercent = .3;
        }
        else
        {
            discountPercent = .1;
        }

        // calculate the discount amount and total
        double discountAmount = subtotal * discountPercent;
        double total = subtotal - discountAmount;

        // format and display the results
        NumberFormat currency = NumberFormat.getCurrencyInstance();
        NumberFormat percent = NumberFormat.getPercentInstance();
        System.out.println(
                "Discount percent: " + percent.format(discountPercent) + "\n" +
                "Discount amount:  " + currency.format(discountAmount) + "\n" +
                "Total:            " + currency.format(total) + "\n");

        // see if the user wants to continue
        System.out.print("Continue? (y/n): ");
        choice = sc.next();
        System.out.println();
    }
}

Answer 1

代码的问题在于变量的范围:如果您在 try block 中声明某些内容，则它仅在该 try block 中可见；它在 try block 之外是不可见的，甚至包括它后面的 catch block 。

为了解决此问题，请在 try block 之外声明变量:

String customerType;
double subtotal;
try {    
//System.out.print("Enter customer type (r/c): ");
    customerType = getValidCustomerType(sc);
    System.out.print("Enter subtotal:   ");
    subtotal = sc.nextDouble();
} catch (InputMismatchException e) {
    sc.next();
    System.out.println("Error! Invalid number. Try again \n");
    continue;
}