我尝试在以下代码中使用嵌套if。我已初始化变量，但编译器告诉我名为＆＃39; bill＆＃39;的变量。即使已经初始化也没有初始化。为什么编译器无法识别赋给变量的值？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
答案 0 :(得分：1)
不，bill尚未在所有情况下初始化。
理解这一点：Java编译器永远不会评估布尔表达式;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，布尔表达式c1和c2可能涵盖所有可能的情况，编译器也无法确保这种情况。
这是您的错误的根本原因，无论您的if / else，switch等语句是否可能嵌套都很深。
答案 1 :(得分：0)
它们是else语句和变量声明的一些问题。 import java.util.Scanner;
class Main {
public static void main(String[] args) {
Scanner console = new Scanner(System.in);
double PREMIUM_SERVICE = 25.00;
double PREMIUM_DAY_OVERTIME_MIN = 0.10;
double PREMIUM_NIGHT_OVERTIME_MIN = 0.05;
double REGULAR_SERVICE = 10.00;
double REGULAR_OVERTIME_MIN = 0.20;
int acctNumber;
double premiumDayMin;
double premiumNightMin;
double bill = 0.0;
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
}
答案 2 :(得分：0)
我不确定为什么会出现此错误，但在声明变量时尝试将bill初始化为0.00。
另外， if（premiumDayMin＆lt; 0＆amp;＆amp; premiumNightMin＆lt; 0）
应该改为
if（premiumDayMin＆lt; 0 || premiumNightMin＆lt; 0）
因为你想确保任何一分钟不小于零。你的程序应该可能会处理这个错误，因为程序的其余部分仍然执行。但也许你正在接受这个:-P。
答案 3 :(得分：0)
我不记得我做了什么来阻止收到错误消息（对不起）但我删除了代码if（premiumDayMin＆lt; 0＆amp;＆amp; premiumNightMin＆lt; 0）并将其替换为if（premiumDayMin＆lt; = 75＆amp;＆amp; premiumNightMin＆lt; = 100）以阻止代码冗余。这可能有固定的东西。如果要进一步清理逻辑，我还添加了另一个。