我已经编辑了这个问题但是在程序的底部我试图编写一个switch语句来验证一些代码。我正在尝试让用户输入Y / N继续。如果他们输入Y，程序应重新启动。如果他们进入N，程序应该结束。如果他们输入Z，他们应该得到一条错误信息并再次提示继续y / n？ 现在，如果我输入一个随机字母，我会被送回数据输入部分，我不知道为什么。
我也注意到我的计算结束了。我假设它与我不使用bigdecimal类的事实有关。目前，如果我输入5.6的百分比，它会自动假设为560％
我是Java的新手，不幸的是苦苦挣扎。昨晚有人非常友好地帮助我而没有公然地给我答案我赞赏，因为它让我自己解决了问题。
由于我在这节课上遇到了困难，所以任何帮助都是绝对值得赞赏的。
import java.util.Scanner;
import java.text.NumberFormat;
public class LoanCalculator
{
public static double getDoubleWithinRange(Scanner sc, String prompt, double min, double max) //validate double
{
double d = 0;
boolean isValid = false;
while(isValid == false)
{
System.out.println(prompt); //print prompt for double
if (sc.hasNextDouble())
{
d = sc.nextDouble();
if (d <= min) //if input <= minimum double
{
System.out.println("Error! Number must be greater than " + min);
System.out.println();//print error grater than min double
}
else if (d >= max) // if input >= maximum double value
{
System.out.println("Error number must be less than " + max);
System.out.println();//print error less than max double value
}
else
isValid = true; //else double is valid
}
else
{
System.out.println("Error! Invalid decimal value.");
System.out.println();
sc.nextLine();
}
}
return d; //return double
}
//validate integer
public static int getIntWithinRange(Scanner sc, String prompt, int min, int max)
{
int i = 0;
boolean isValid = false;
while(isValid == false)
{
System.out.println(prompt); //print prompt for integer
if (sc.hasNextInt())
{
i = sc.nextInt();
if (i <= min) //if input <= minimum integer
{
System.out.println("Error! Number must be greater than " + min);
System.out.println();//print error grater than min integer
}
else if (i >= max) // if input >= maximum integer value
{
System.out.println("Error number must be less than " + max);
System.out.println();//print error less than max integer value
}
else
isValid = true; //else integer is valid
}
else
{
System.out.println("Error! Invalid integer value.");
System.out.println();
sc.nextLine();
}
}
return i; //return integer
}
public static void main(String[] args)
{
System.out.println("Welcome to the loan calculator"); //welcome user to loan calculator
Scanner sc = new Scanner(System.in); // create new scanner
String choice = "y"; //start choice loop
while (choice.equalsIgnoreCase("y"))
{
System.out.println();
System.out.println("DATA ENTRY");
double loanAmount = getDoubleWithinRange(sc, "Enter loan amount: ", 0.0, 1000000.0); //get user input for loanAmount
//get user input for interestRate
double interestRate = getDoubleWithinRange(sc, "Enter yearly interest rate: ", 0, 20);
//get user input for years
int years = getIntWithinRange(sc, "Enter number of years: ", 0, 100);
int months = years * 12; // calculate years to months
//calculate monthly payment
double monthlyPayment = loanAmount * interestRate/ (1 - 1 / Math.pow(1 + interestRate, months));
//import currency instance
NumberFormat currency = NumberFormat.getCurrencyInstance();
// import percent instance
NumberFormat percent = NumberFormat.getPercentInstance();
percent.setMinimumFractionDigits(1); //set fraction digits for percent
System.out.println("RESULST"); //print results
//print loanAmount
System.out.println("Loan Amount: " + currency.format(loanAmount));
//print interestRate
System.out.println("Yearly interest rate: " + percent.format(interestRate));
System.out.println("Number of years: " + years); //print years
//print monthlyPayment
System.out.println("Monthly payment: " + currency.format(monthlyPayment));
boolean quit = false;
do {
System.out.println();
System.out.println("Continue? (y/n): "); //prompt user to continue
String userinput1 = sc.next();
char choice1 = userinput1.toLowerCase().charAt(0);
switch (choice1) {
case 'y':
break;
case 'n':
// case n, do something here
quit = true;
break;
case ' ':
System.out.println("Error! This entry is required. Try again.");
break;
default:
System.out.println("Error! Entry must be 'y or 'n''");
break;
}
} while (!quit);
}
}
}
答案 0 :(得分：2)
像这样使用switch：
boolean quit = false;
do{ // change your while by this
// your own stuff here
// then after all your program stuff
boolean choiceIsOK = false;
do{
String userinput = sc.next();
char choice = userinput.toLowerCase().charAt(0);
switch(choice){
case 'y':
// case y, do nothing, you could even remove that case.
choiceIsOK = true;
break;
case 'n':
// case n, do something here
choiceIsOK = false;
quit = true;
break;
default:
// error or warning
System.out.println("Type Y or N to respectively continue or quit");
break;
}
}while(!choiceIsOK);
}while (!quit);
在您的代码中，它将如下所示：
public static void main(String[] args)
{
System.out.println("Welcome to the loan calculator"); //welcome user to loan calculator
Scanner sc = new Scanner(System.in); // create new scanner
//String choice = "y"; //start choice loop [no need for that line anymore]
boolean quit = false;
do{
System.out.println();
System.out.println("DATA ENTRY");
double loanAmount = getDoubleWithinRange(sc, "Enter loan amount: ",
0.0, 1000000.0); //get user input for loanAmount
//get user input for interestRate
double interestRate = getDoubleWithinRange(sc,
"Enter yearly interest rate: ", 0, 20);
//get user input for years
int years = getIntWithinRange(sc, "Enter number of years: ", 0, 100);
int months = years * 12; // calculate years to months
//calculate monthly payment
double monthlyPayment = loanAmount * interestRate/
(1 - 1/Math.pow(1 + interestRate, months));
//import currency instance
NumberFormat currency = NumberFormat.getCurrencyInstance();
// import percent instance
NumberFormat percent = NumberFormat.getPercentInstance();
percent.setMinimumFractionDigits(1); //set fraction digits for percent
System.out.println("RESULST"); //print results
//print loanAmount
System.out.println("Loan Amount: " + currency.format(loanAmount));
//print interestRate
System.out.println("Yearly interest rate: " + percent.format(interestRate));
System.out.println("Number of years: " + years); //print years
//print monthlyPayment
System.out.println("Monthly payment: " + currency.format(monthlyPayment));
// then after all your program stuff
boolean choiceIsOK = false;
do{
System.out.println();
System.out.println("Continue? (y/n): "); //prompt user to continue
String userinput1 = sc.next();
char choice1 = userinput1.toLowerCase().charAt(0);
switch(choice1){
case 'y':
// case y, do nothing, you could even remove that case.
choiceIsOK = true;
break;
case 'n':
// case n, do something here
choiceIsOK = true; // I fixed this
quit = true;
break;
default:
// error or warning
System.out.println("Type Y or N to respectively continue or quit");
break;
}
}while(!choiceIsOK);
}while(!quit);
}
}
答案 1 :(得分：1)
使用if声明，
choice =sc.next().toLowerCase();
if(choice.equals("y"))
{
//
}
else
if(choice.equals("n"))
{
//
}
else
{
//invalid input
}
答案 2 :(得分：1)
您必须使用条件，这些格式为
if(someBooleanCondition){
doSomething();
}
else{
doSomethingElse();
}
在您的情况下，您将使用String.equals()函数作为布尔条件。 NOT ==因为这会给字符串带来奇怪的结果。所以你应该做这样的事情。
String userInput = sc.next().toLowerCase();
if(userInput.equals("y")){
//Its yes, do something here
}
else if(userInput.equals("n")){
//It's no, do something else
}
else{
//Handle an invalid entry here
}
这种循环使其反复检查输入的方法是：
while(true)
String userInput = sc.next().toLowerCase();
if(userInput.equals("y")){
//Its yes, do something here
break;
}
else if(userInput.equals("n")){
//It's no, do something else
break;
}
else{
//Handle an invalid entry here
}
这将强制用户继续输入内容，直到他们输入Y或N，如果您希望他们能够输入换行符退出，或者您可以将其添加到循环中。