While 循环不会重新运行程序，只询问是否要再次循环

Question

我正在尝试提示用户输入 Y、y 或 N、n，并使用 while 循环询问他们是否要重新运行程序。我尝试使用 this question 中的代码。我更改了字符串选择 = sc.next();到 in.next();当我运行程序时，一切正常，但是当出现提示并且我回答 y 时，它只会询问我是否要再次运行而不实际运行程序（让用户输入和输出答案）。 n 将正常工作并结束它。感谢您的时间！这让我在这里、youtube 和其他编码论坛上寻找答案很多个晚上。

编辑：我尝试将与贷款相关的代码移动到 while 循环中（在 while 和 boolean 之间），但现在它完全跳过“你想再次计算（y/n）：”并直接进入“输入贷款金额：" 不问

package numformexception;

import java.util.Scanner;

public class NumFormException {

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
    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
    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));


    System.out.printf("The monthly payment is: $ %.2f%n", outputNum);


    boolean isContinuing = true;

    while( isContinuing) {
        boolean inputIsInvalid = true;
        while (inputIsInvalid) {
            System.out.print("Would you like to calculate again (y/n): ");

            String choice = in.next();

            if("y".equalsIgnoreCase(choice)) {
                inputIsInvalid = false;

            }
            else if("n".equalsIgnoreCase(choice)){
                inputIsInvalid = false;
                isContinuing = false;
            }
            else {
                System.err.print("Error: Only valid answers are Y/N. ");
            }

        }
    }
}

}

Answer 1

你的主计算不会再次运行，因为它不是这个循环的一部分：

while (isContinuing) {
    // ...
}

我建议把主要的计算逻辑移到一个方法中，例如：

private static void calculateLoan(Scanner in) {
    //Declare Variables
    double loanNum;
    double rateNum;
    double trateNum;
    double yearNum;
    double monthNum;
    double equNum;
    double outputNum;

    //Prompt for input
    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
    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));

    System.out.printf("The monthly payment is: $ %.2f%n", outputNum);
}

然后更改main 方法，使其在循环内调用新的calculateLoan 方法：

public static void main(String[] args) {

    Scanner in = new Scanner(System.in);

    boolean isContinuing = true;

    while (isContinuing) {

        calculateLoan(in);

        boolean inputIsInvalid = true;
        while (inputIsInvalid) {
            System.out.print("Would you like to calculate again (y/n): ");

            String choice = in.next();

            if ("y".equalsIgnoreCase(choice)) {
                inputIsInvalid = false;

            } else if ("n".equalsIgnoreCase(choice)) {
                inputIsInvalid = false;
                isContinuing = false;
            } else {
                System.err.print("Error: Only valid answers are Y/N. ");
            }

        }
    }
}

Answer 2

唯一会循环的代码是在您的 while 循环中的代码。因此，与贷款相关的代码都不会循环是完全有道理的。如果您希望它循环，您必须首先将其放入一个循环中，可能在 while 继续 while 循环中，该循环应该包含您的 main 方法中的几乎所有内容，变量声明之后的所有内容。