While语句循环错误

Question

Hey I have been having an issue with this code because it has not been looping when I input a value for the String repeat. I am unable to understand whatever it is that I'm doing wrong.

import java.util.Scanner;
public class MpgCalculator
{
    public static void main(String[]args)
    {
        Scanner sc = new Scanner(System.in);
        System.out.println("Welcome to the MPG and CPM Calculator!");
        double startOd, endOd, gallons, cost, mpg, cpm;
        String repeat = "yes";
        while(repeat.equals("yes")||repeat.equals("Yes")||repeat.equals("y")||repeat.equals("Y"))
        {
            System.out.println("Please Enter:");
            System.out.print("\tYour Starting Odometer Reading: ");
            startOd = sc.nextDouble();
            System.out.print("\tYour Ending Odometer Reading: ");
            endOd = sc.nextDouble();
            System.out.print("\tThe Amount of Gallons Used: ");
            gallons = sc.nextDouble();
            System.out.print("\tThe Cost-per-Gallon That You Spent: ");
            cost = sc.nextDouble();
            mpg = getMpg(startOd, endOd, gallons);
            cpm = getCpm(mpg, cost);
            System.out.println("\nYour Miles-per-Gallon is " + mpg + ".");
            System.out.println("Your Cost-per-Mile is " + cpm + ".");
            System.out.print("Do it again? ");
            repeat = sc.nextLine();
        }
    }
    public static double getMpg(double startOd, double endOd, double gallons)
    {
        double mpg;
        mpg = (endOd - startOd) / gallons;
        return mpg;
    }
    public static double getCpm(double mpg, double cost)
    {
        double cpm;
        cpm = cost / mpg;
        return cpm;
    }
}

Answer 1

Change repeat = sc.nextLine(); to repeat = sc.next(); If you don't need the extra line. It only gets it if you are an the next line, which you are not, so it terminates the program.

Answer 2

The previous use of your Scanner prior to calling repeat = sc.nextLine(); in your while loop is nextDouble . Calling nextDouble does not consume the newline character in the stream from entering the cost per gallon.

Consume the newline character before asking to repeat:

System.out.print("Do it again? ");
String dummy = sc.nextLine();  // Add this line.
repeat = sc.nextLine();

Answer 3

use repeat = sc.next(); instead of repeat = sc.nextLine();