问题:
互联网服务提供了三种不同的订阅包:
套餐1:每月$ 15.95，最多可使用10小时。额外的时间为每小时$ 2.00。
套餐2:每月20.95美元，最多可使用20个小时。额外的时间为每小时$ 1.00。
套餐3:每月30.99美元，无限制访问。
编写一个执行以下操作的程序:
询问用户他们有什么计划。
向用户询问要为其支付账单的月份号(1-12)。
询问用户他们使用了几个小时。
显示其帐单费用。
还显示Package 1客户如果购买Package 2或3将节省多少钱，以及Package 2客户如果购买Package 3将节省多少钱。
如果没有节省，则不显示此消息。
输入验证:
计划编号不能为负。
计划编号必须为值[1、3]。
小时数不能为负。
小时数不能超过给定月份的小时总数。
30天的月份为720小时，31天的月份为744小时，2月28天的为672小时(不必担心leap年)。
验证用户输入的值不大于给定月份的总小时数。
请参见下表。
月，天，小时。
744年1月31日。
672年2月28日。
744年3月31日。
720年4月30日。
744年5月31日。
720年6月30日。
744年7月31日。
744年8月31日。
720年9月30日。
744年10月31日。
720年11月30日。
744年12月31日。
我的问题。
我的变量有问题。我知道有更好的方法来编写此程序，但是您应该记住，这是我第四周用Java编写代码。
当我尝试编译它时，我使用了过多的if语句；我得到一些变量的12错误。我假设它的变量范围被某个if语句阻塞。因为编译器要求初始化变量，即使它们之前已经初始化过。
任何帮助将不胜感激 :)
/*
* Homework 04 Problem 05
* Student: Kevin Crespin
* CIN:
* Description: This program does the following:
* Ask the user which plan they have.
* Ask the user for the month number (1-12) of which month they are being billed.
* Ask the user how many hours they used.
* Display the cost of their bill.
* Also display how much money Package 1 customers would would have saved if they purchased
* packages 2 or 3, and how much money Package 2 customers would have saved if they purchased
* Package 3. If there were no savings, do not display this message.
*/
// import scanner class
import java.util.Scanner;
public class HW04P05{
public static void main (String[] args) {
Scanner input = new Scanner(System.in);
// USER MENU
final String USER_MENU =
" \n" +\
"[1] Package 1: $15.95 a month for up to 10 hours of service. Additional hours are $2.00 per hour.\n" +
"[2] Package 2: $20.95 a month for up to 20 hours of service. Additional hours are $1.00 per hour.\n" +
"[3] Package 3: $30.99 per month unlimited access.\n" +
" \n" +
"Enter [1 - 3] for select your package: ";
final int PACKAGE_1 = 1;
final int PACKAGE_2 = 2;
final int PACKAGE_3 = 3;
System.out.print(USER_MENU);
int choice = input.nextInt();
System.out.println(" ");
if (choice < 0) {
System.out.println("The menu choice cannot be negative, must be a value [1 - 3]");
System.out.println("The program will know exit.");
System.exit(1);
}
else if (choice == 0) {
System.out.println("The menu choice cannot be zero, must be a value [1 - 3]");
System.out.println("The program will know exit.");
System.exit(1);
}
else if (choice > 3) {
System.out.println("The menu choice must be a value [1 - 3]");
System.out.println("The program will know exit.");
System.exit(1);
}
System.out.print("[1] January [4] April [7] July [10] October\n");
System.out.print("[2] February [5] May [8] August [11] November\n");
System.out.print("[3] March [6] June [9] September [12] December\n");
System.out.println(" ");
System.out.print("Enter [1 - 12] for select billed month: ");
int month = input.nextInt();
if (month < 0) {
System.out.println("The month cannot be negative, must be a value [1 - 12]");
System.out.println("The program will know exit.");
System.exit(1);
}
else if (month == 0) {
System.out.println("The month cannot be zero, must be a value [1 - 12]");
System.out.println("The program will know exit.");
System.exit(1);
}
else if (month > 12) {
System.out.println("The month must be a value [1 - 12]");
System.out.println("The program will know exit.");
System.exit(1);
}
double hours;
double savings_1;
double savings_2;
double total_1;
double total_2;
final double total_1d = 15.95;
final double total_2d = 20.95;
final double total_3d = 30.99;
// USER MENU SWITCH
switch (choice) {
case PACKAGE_1:
if ((month == 1) ^ (month == 3) ^ (month == 5) ^ (month == 7) ^ (month == 8) ^ (month == 10) ^ (month == 12)) {
System.out.print("Enter the number of hours the plan package was used: ");
hours = input.nextInt();
if (hours > 744) {
System.out.println("ERROR: The number of hours cannot be higher than 744 on the month selected.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else if (hours < 0) {
System.out.println("ERROR: The number of hours cannot be negative.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else {
if (hours < 10 && hours >= 1){
System.out.println("The cost of your bill is: $15.95");
}
else if (hours > 10 && hours <= 744) {
total_1 = ((hours - 10) * 2) + 15.95;
System.out.println("The cost of your bill is: $" + total_1);
}
}
}
else if (month == 2) {
System.out.print("Enter the number of hours the plan package was used: ");
hours = input.nextInt();
if (hours > 672) {
System.out.println("ERROR: The number of hours cannot be higher than 672 on February.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else if (hours < 0) {
System.out.println("ERROR: The number of hours cannot be negative.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else {
if (hours < 10 && hours >= 1){
System.out.println("The cost of your bill is: $15.95");
}
else if (hours > 10 && hours <= 672) {
total_1 = ((hours - 10) * 2) + 15.95;
System.out.println("The cost of your bill is: $" + total_1);
}
}
}
else {
System.out.print("Enter the number of hours the plan package was used: ");
hours = input.nextInt();
if (hours > 720) {
System.out.println("ERROR: The number of hours cannot be higher than 722 on the month selected.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else if (hours < 0) {
System.out.println("ERROR: The number of hours cannot be negative.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else {
if (hours < 10 && hours >= 1){
System.out.println("The cost of your bill is: $15.95");
}
else if (hours > 10 && hours <= 720) {
total_1 = ((hours - 10) * 2) + 15.95;
System.out.println("The cost of your bill is: $" + total_1);
}
}
}
case PACKAGE_2:
if ((month == 1) ^ (month == 3) ^ (month == 5) ^ (month == 7) ^ (month == 8) ^ (month == 10) ^ (month == 12)) {
if (choice == 2) {
System.out.print("Enter the number of hours the plan package was used: ");
hours = input.nextInt();
if (hours > 744) {
System.out.println("ERROR: The number of hours cannot be higher than 744 on the selected month.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else if (hours < 0) {
System.out.println("ERROR: The number of hours cannot be negative.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else {
if (hours < 20 && hours >= 1) {
System.out.println("The cost of your bill is: $20.95");
}
else if (hours > 20 && hours <= 744) {
total_2 = (hours - 20) + 20.95;
System.out.println("The cost of your bill is: $" + total_2);
}
}
}
else {
if (hours < 20 && hours >= 1) {
System.out.println("The cost of package 2 bill is: $20.95");
savings_1 = total_1 - total_2d;
System.out.println("You could saved: $" + savings_1);
}
else if (hours > 20 && hours <= 744) {
total_2 = (hours - 20) + 20.95;
System.out.println("The cost of package 2 bill is: $" + total_2);
savings_1 = total_1 - total_2d;
System.out.println("You could saved: $" + savings_1);
}
}
else if (month == 2) {
if (choice == 2) {
System.out.print("Enter the number of hours the plan package was used: ");
hours = input.nextInt();
if (hours > 672) {
System.out.println("ERROR: The number of hours cannot be higher than 672 on February.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else if (hours < 0) {
System.out.println("ERROR: The number of hours cannot be negative.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else {
if (hours < 20 && hours >= 1){
System.out.println("The cost of your bill is: $20.95");
}
else if (hours > 20 && hours <= 672) {
total_2 = (hours - 20) + 20.95;
System.out.println("The cost of your bill is: $" + total_2);
}
}
}
else {
if (hours < 20 && hours >= 1) {
System.out.println("The cost of package 2 bill is: $20.95");
savings_1 = total_1 - total_2d;
System.out.println("You could saved: $" + savings_1);
}
else if (hours > 20 && hours <= 672) {
total_2 = (hours - 20) + 20.95;
System.out.println("The cost of package 2 bill is: $" + total_2);
savings_1 = total_1 - total_2d;
System.out.println("You could saved: $" + savings_1);
}
}
}
else {
if (choice == 2) {
System.out.print("Enter the number of hours the plan package was used: ");
hours = input.nextInt();
if (hours > 720) {
System.out.println("ERROR: The number of hours cannot be higher than 722 on the selected month.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else if (hours < 0) {
System.out.println("ERROR: The number of hours cannot be negative.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else {
if (hours < 20 && hours >= 1){
System.out.println("The cost of your bill is: $20.95");
}
else if (hours > 20 && hours <= 720) {
total_2 = (hours - 20) + 20.95;
System.out.println("The cost of your bill is: $" + total_2);
}
}
}
else {
if (hours < 20 && hours >= 1) {
System.out.println("The cost of package 2 bill is: $20.95");
savings_1 = total_1 - total_2d;
System.out.println("You could saved: $" + savings_1);
}
else if (hours > 20 && hours <= 720) {
total_2 = (hours - 20) + 20.95;
System.out.println("The cost of package 2 bill is: $" + total_2);
savings_1 = total_1 - total_2d;
System.out.println("You could saved: $" + savings_1);
}
}
}
case PACKAGE_3:
if ((month == 1) ^ (month == 3) ^ (month == 5) ^ (month == 7) ^ (month == 8) ^ (month == 10) ^ (month == 12)) {
if (choice == 3) {
System.out.print("Enter the number of hours you used your plan package: ");
hours = input.nextInt();
if (hours > 744) {
System.out.println("Enter the number of hours the plan package was used: ");
System.out.println("Now the program will exit.");
System.exit(1);
}
else if (hours < 0) {
System.out.println("ERROR: The number of hours cannot be negative.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else {
System.out.println("The cost of your bill is: $30.99");
}
}
else {
System.out.println("The cost of package 3 bill is: $30.99");
savings_2 = total_1 - total_3d;
System.out.println("You could saved: $" + savings_2);
}
}
else if (month == 2) {
if (choice == 3) {
System.out.print("Enter the number of hours the plan package was used: ");
hours = input.nextInt();
if (hours > 672) {
System.out.println("ERROR: The number of hours cannot be higher than 672 on February.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else if (hours < 0) {
System.out.println("ERROR: The number of hours cannot be negative.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else {
System.out.println("The cost of your bill is: $30.99");
}
}
else {
System.out.println("The cost of package 3 bill is: $30.99");
savings_2 = total_1 - total_3d;
System.out.println("You could saved: $" + savings_2);
}
}
else {
if (choice == 3) {
System.out.print("Enter the number of hours the plan package was used: ");
hours = input.nextInt();
if (hours > 720) {
System.out.println("ERROR: The number of hours cannot be higher than 720 on the selected month.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else if (hours < 0) {
System.out.println("ERROR: The number of hours cannot be negative.");
System.out.println("Now the program will exit.");
System.exit(1);
}
else {
System.out.println("The cost of your bill is: $30.99");
}
}
else {
System.out.println("The cost of package 3 bill is: $30.99");
savings_2 = total_1 - total_3d;
System.out.println("You could saved: $" + savings_2);
}
}
}
}
}
编译代码会产生以下结果:
HW04P05.java:176: error: variable hours might not have been initialized
if (hours < 20 && hours >= 1) {
^
HW04P05.java:178: error: variable total_1 might not have been initialized
savings_1 = total_1 - total_2d;
^
HW04P05.java:184: error: variable total_1 might not have been initialized
savings_1 = total_1 - total_2d;
^
HW04P05.java:214: error: variable hours might not have been initialized
if (hours < 20 && hours >= 1) {
^
HW04P05.java:216: error: variable total_1 might not have been initialized
savings_1 = total_1 - total_2d;
^
HW04P05.java:222: error: variable total_1 might not have been initialized
savings_1 = total_1 - total_2d;
^
HW04P05.java:252: error: variable hours might not have been initialized
if (hours < 20 && hours >= 1) {
^
HW04P05.java:254: error: variable total_1 might not have been initialized
savings_1 = total_1 - total_2d;
^
HW04P05.java:260: error: variable total_1 might not have been initialized
savings_1 = total_1 - total_2d;
^
HW04P05.java:286: error: variable total_1 might not have been initialized
savings_2 = total_1 - total_3d;
^
HW04P05.java:310: error: variable total_1 might not have been initialized
savings_2 = total_1 - total_3d;
^
HW04P05.java:334: error: variable total_1 might not have been initialized
savings_2 = total_1 - total_3d;
^
12 errors
最佳答案
出现错误的原因是代码中的某些执行路径未将值设置为hours。很难看到此问题，因为您将输入验证与结果计算逻辑混合在一起。
您可以将小时数初始化为0，但是我怀疑您的程序仍然无法按照您期望的方式运行。
尽管有很多方法可以解决此问题，但我建议将代码分成许多较小的部分，以分别解决每个问题。这样做有许多优点，包括能够分别测试每个零件，并使其更易于理解，更重要的是，它更易于维护。
如果将每个部分分成自己的方法，则主方法可能如下所示:
public static void main(String[] args) {
int plan = getPlanFromUser();
int month = getMonthFromUser();
int hours = getHoursFromUser(month);
evaluateSavings(plan, month, hours);
}
然后，要从用户那里获取计划，请编写一个名为getPlanFromUser()的方法，该方法将检索用户的输入并在返回有效选择之前对其进行验证。
与其他“获取”方法类似，特殊情况是
getHoursFromUser()，您在其中传递月份，以便该方法可以验证是否输入了正确的小时数。最后，您的
evaluateSavings()方法接收所有用户输入(已经验证)，并简单地计算适当的节省。采用这种方法意味着您只需要解决每种方法中的几个问题，而不必同时考虑所有问题。
编辑:这是如上所述重组的代码
import java.util.Scanner;
public class HW04P05 {
private static final int PACKAGE_1 = 1;
private static final int PACKAGE_2 = 2;
private static final int PACKAGE_3 = 3;
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int plan = getPlan(input);
int month = getMonth(input);
int hours = getHours(input, month);
calculateSavings(plan, hours);
}
private static int getPlan(Scanner input) {
// packages menu
System.out.println();
System.out.println("[1] Package 1: $15.95 a month for up to 10 hours of service. Additional hours are $2.00 per hour.");
System.out.println("[2] Package 2: $20.95 a month for up to 20 hours of service. Additional hours are $1.00 per hour.");
System.out.println("[3] Package 3: $30.99 per month unlimited access.");
System.out.println();
System.out.print("Enter [1 - 3] for select your package: ");
// get input
int choice = input.nextInt();
// input validation
System.out.println(" ");
if (choice < 0) {
exitProgram("The menu choice cannot be negative, must be a value [1 - 3]");
} else if (choice == 0) {
exitProgram("The menu choice cannot be zero, must be a value [1 - 3]");
} else if (choice > 3) {
exitProgram("The menu choice must be a value [1 - 3]");
}
return choice;
}
private static int getMonth(Scanner input) {
// month menu
System.out.println("[1] January [4] April [7] July [10] October");
System.out.println("[2] February [5] May [8] August [11] November");
System.out.println("[3] March [6] June [9] September [12] December");
System.out.println("");
System.out.print("Enter [1 - 12] for select billed month: ");
// get input
int month = input.nextInt();
// input validation
if (month < 0) {
exitProgram("The month cannot be negative, must be a value [1 - 12]");
} else if (month == 0) {
exitProgram("The month cannot be zero, must be a value [1 - 12]");
} else if (month > 12) {
exitProgram("The month must be a value [1 - 12]");
}
return month;
}
private static int getHours(Scanner input, int month) {
// hours menu
System.out.println(" ");
System.out.print("Enter the number of hours the plan package was used: ");
// get input
int hours = input.nextInt();
// input validation
if (hours < 0) {
exitProgram("ERROR: The number of hours cannot be negative.");
}
if ((month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) && hours > 744) {
exitProgram("ERROR: The number of hours cannot be higher than 744 on the month selected.");
}
if ((month == 4 || month == 6 || month == 9 || month == 11) && hours > 720) {
exitProgram("ERROR: The number of hours cannot be higher than 720 on the month selected.");
}
if (month == 2 && hours > 672) {
exitProgram("ERROR: The number of hours cannot be higher than 672 on the month selected.");
}
return hours;
}
private static void calculateSavings(int plan, int hours) {
double pricePlan1 = calculatePricePlan1(hours);
double pricePlan2 = calculatePricePlan2(hours);
double pricePlan3 = 30.99;
switch(plan) {
case PACKAGE_1:
System.out.println(String.format("The cost of your bill is: $%.2f", pricePlan1));
if (pricePlan1 > pricePlan2) {
System.out.println(String.format("On package 2 you could have saved $%.2f", pricePlan1 - pricePlan2));
}
if (pricePlan1 > pricePlan3) {
System.out.println(String.format("On package 3 you could have saved $%.2f", pricePlan1 - pricePlan3));
}
break;
case PACKAGE_2:
System.out.println(String.format("The cost of your bill is: $%.2f", pricePlan2));
if (pricePlan2 > pricePlan3) {
System.out.println(String.format("On package 3 you could have saved $%.2f", pricePlan2 - pricePlan3));
}
break;
case PACKAGE_3:
System.out.println(String.format("The cost of your bill is: $%.2f", pricePlan3));
break;
}
}
private static double calculatePricePlan1(int hours) {
if (hours <= 10) {
return 15.95;
}
return 15.95 + ((hours - 10) * 2);
}
private static double calculatePricePlan2(int hours) {
if (hours <= 20) {
return 20.95;
}
return 20.95 + (hours - 20);
}
private static void exitProgram(String reason) {
System.out.println(reason);
System.out.println("The program will now exit.");
System.exit(1);
}
}
请注意，每种方法都适合一个“页面”，并且每种方法都可以独立理解和测试。这种方法使其他开发人员更容易理解代码的作用(从而降低了维护成本)。
关于java - Java : ERROR variable scopes in if statements，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/46288877/