java - 需要有关嵌套 if 的建议

Question

我尝试在下面的代码中使用嵌套的 if 。我已经初始化了变量，但编译器告诉我名为“bill”的变量尚未初始化，即使它已初始化。为什么编译器无法识别分配给变量的值？请参阅下面代码中的注释。

package killMe;

import java.util.Scanner;

public class Kill_Me {

static Scanner console = new Scanner(System.in);

    static double PREMIUM_SERVICE = 55.00;
    static double PREMIUM_DAY_OVERTIME_MIN = 0.20;
    static double PREMIUM_NIGHT_OVERTIME_MIN = 0.15;
    static double REGULAR_SERVICE = 30.00;
    static double REGULAR_OVERTIME_MIN = 0.40;

    public static void main(String[] args) {
        int acctNumber; 
        double premiumDayMin;
        double premiumNightMin;
        double bill;
        double minutes;
        String name;
        String premium = "PREMIUM";
        String regular = "REGULAR";

        System.out.println("What is the Account Number? ");
        acctNumber = console.nextInt();
        System.out.println("What is the Customer Name? ");
        name = console.next();
        System.out.println("Is the Service Code Premium or Regular? ");
        String strService = console.next();
        String strServiceCAP = strService.toUpperCase();


        if(strServiceCAP.compareTo(premium) == 0)
        {
                 System.out.println("How many Day Minutes were used? ");
                 premiumDayMin = console.nextDouble();
                 System.out.println("How many Night Minutes were used? ");
                 premiumNightMin = console.nextDouble();


                 if(premiumDayMin <0 && premiumNightMin <0)
                 {
                     System.out.println("Minutes cannot be less than 0 ");
                 }
                 else if(premiumDayMin <= 75 && premiumNightMin <= 100)
                 {
                     bill = PREMIUM_SERVICE;
                 }
                 else bill = PREMIUM_SERVICE + (premiumDayMin - 75) * PREMIUM_DAY_OVERTIME_MIN + (premiumNightMin - 100)
                         * PREMIUM_NIGHT_OVERTIME_MIN;

                 minutes = premiumDayMin + premiumNightMin;

                System.out.println("Customer Name:  " + name);
                System.out.println("Account Number:  " + acctNumber);
                System.out.println("Service Type:  " + strServiceCAP);
                System.out.println("Minutes Premium Service Used (Day):  " + premiumDayMin);
                System.out.println("Minutes Premium Service Used (Night):  " + premiumNightMin);
                System.out.println("Amount Due:  " + bill); // I get an error here stating, "The local variable 'bill' may not have been initialized". 
        }
        else if(strServiceCAP.compareTo(regular) == 0)
        {
                System.out.println("How many minutes were used? ");
                minutes = console.nextDouble();
                bill = REGULAR_SERVICE + (minutes - 50) * REGULAR_OVERTIME_MIN; 

                System.out.println("Customer Name:  " + name);
                System.out.println("Account Number:  " + acctNumber);
                System.out.println("Service Type:  " + strServiceCAP);
                System.out.println("Minutes Regular Service Used:  " + minutes);
                System.out.println("Amount Due:  " + bill); // I DO NOT receive an error message here. 


        }
        else
        {
            System.out.println("Invalid Service Type");
        }


    } // End of main

} // End of class

Answer 1

否，bill 在所有情况下均未初始化。

理解这一点:Java 编译器永远不会计算 boolean 表达式；简化版:

double bill;

if (c1) {
    bill = v1;
} else if (c2) {
    bill = v2;
}

// try and use bill here

即使，根据您的逻辑， boolean 表达式 c1 和 c2 可能涵盖所有可能的情况，编译器也无法确保这是案例。

无论 if/else、switch 等语句嵌套得有多深，这都是错误的根本原因。