1
尝试捕捉我必须做出一个计算器,将While循环:负输入检查和添加字符串
用正数输入,显示输出运行程序,如果用户想循环问。
使用字符串输入(两个而不是2)运行程序,使用try和catch来显示一条消息,告诉用户错误,并询问用户是否想要循环。
使用负数输入运行程序,显示错误消息而不显示输出,并询问用户是否要循环。
当我试图捕捉我得到variable not have been initialized
为try catch
后的变量。
try {
System.out.print("Enter loan amount: ");
loanNum = Double.parseDouble(in.nextLine());
System.out.print("Enter rate: ");
rateNum = Double.parseDouble(in.nextLine());
System.out.print("Enter number years: ");
yearNum = Double.parseDouble(in.nextLine());
}
catch(NumberFormatException e) {
System.out.println ("You must enter positive numeric data!");
}
没有try catch
我想不出该怎么办2号,而不使用System.exit(0);
不显示输出。这终止了用户能够输入到循环。
我不知道如何解决我的while循环。当我运行程序时,它只会运行一次,然后循环一次。之后,它会自动循环,而不提示和吐出像一行行:
Would you like to calculate again (y/n):
Enter loan amount:
代码:
package whileloopyn;
import java.util.Scanner;
public class Whileloopyn {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
//Declare Variables
double loanNum;
double rateNum;
double trateNum;
double yearNum;
double monthNum;
double equNum;
double outputNum;
//Prompt for input and try catch for exception error (rate inputed as two)
System.out.print("Enter loan amount: ");
loanNum = Double.parseDouble(in.nextLine());
System.out.print("Enter rate: ");
rateNum = Double.parseDouble(in.nextLine());
System.out.print("Enter number years: ");
yearNum = Double.parseDouble(in.nextLine());
//Postive input data check (negative then ask again)
if(loanNum <= 0 || rateNum <=0 || yearNum <=0)
{
System.out.println("You must enter positive numeric data! ");
System.exit(0);
}
//Convert years to months
monthNum = yearNum * 12;
//Convert rate to percent and monthly
trateNum= (rateNum/100) /12;
//Complete numerator
equNum = Math.pow((1+ trateNum), monthNum);
//Plug equNum into formula
outputNum = trateNum * loanNum * (equNum/(equNum - 1));
//output answer
System.out.printf("The monthly payment is: $ %.2f%n", outputNum);
//prompt user y n to run program again
System.out.println("Would you like to calculate again (y/n): ");
String loop = in.nextLine();
//while loop with (input
boolean isContinuing = true;
while (isContinuing) {
while(loop.equals("y")){
System.out.print("Enter loan amount: ");
loanNum = in.nextDouble();
System.out.print("Enter rate: ");
rateNum = in.nextDouble();
System.out.print("Enter number years: ");
yearNum = in.nextDouble();
//Postive input data check (negative then loop again)
if(loanNum <= 0 || rateNum <=0 || yearNum <=0)
{
System.out.println("You must enter positive numeric data! ");
System.exit(0);
}
//Convert years to months
monthNum = yearNum * 12;
//Convert rate to percent and monthly
trateNum= (rateNum/100) /12;
//Complete numerator
equNum = Math.pow((1+ trateNum), monthNum);
//Plug equNum into formula
outputNum = trateNum * loanNum * (equNum/(equNum - 1));
//output answer
System.out.printf("The monthly payment is: $ %.2f%n", outputNum);
//ask user if you want to use program again
System.out.printf("Would you like to calculate again (y/n): ");
if(loop.equals("n"))
{
System.exit(0);
}
}
}
}
}
有人建议(input.equals(String)
)是我应该如何比较的字符串while循环并使用in.nextLine();
。
你真正需要得到输入,如果你问用户,而不是直接进入if条件。你也需要通过调用'nextLine'来使用任何'nextFoo'(不包括'nextLine')方法来捕获回车符。对于此检查的参考[this](http://stackoverflow.com/questions/13102045/skipping-nextline-after-using-next-nextint-or-other-nextfoo-methods) – SomeJavaGuy