java - 我怎样才能退出这个 while 循环并使其在有人输入 "? quit"时程序将终止

Question

import java.util.Scanner;
public class RectAngleObj {
public static void main(String args[]) {
    String sPeri = "perimeter";
    String sArea = "area";
    String sQues = "?";
    String sQuit = "quit";
    String f;
    String g;
    String h;
    String j;

    Scanner sc = new Scanner(System.in);

    while(sc.hasNext()){
        f = sc.next(); // assigns the first standard input to f (can either be ? or quit)
        g = sc.next(); // assigns the second word from standard input to g (can either be perimeter or area)
        if(f.equals(sQues)) { // if first word is equal to "?" then the if statements continue
            if (g.equals(sPeri)) { // if the second word is equal to "perimeter" print out result
                double a = sc.nextDouble(), // assigns next four doubles to a, b, c, d
                       b = sc.nextDouble(),
                       c = sc.nextDouble(),
                       d = sc.nextDouble();
                RectAngle3 r = new RectAngle3(a, b, c, d); // creates an object of RectAngle3 with dimensions of a, b, c, d
                System.out.println("Perimeter of (" + r.rectNums() + "): "  + r.rectPeri());
            } if (g.equals(sArea)) { // if the second word is equal to "area" print out result
                double a = sc.nextDouble(), // assigns next four doubles to a, b, c, d
                       b = sc.nextDouble(),
                       c = sc.nextDouble(),
                       d = sc.nextDouble();
                RectAngle3 r = new RectAngle3(a, b, c, d); // creates an object of RectAngle3 with dimensions of a, b, c, d
                System.out.println("Area of (" + r.rectNums() + "): " + r.rectArea());
            }
    }
    }
    }
}       

我希望 while 循环自然结束，而不使用 System.exit(0);或打破；请帮忙!

理想情况下，如果有人输入“? quit”，程序就会结束。

我没有收到任何错误，循环会永远持续下去...不知道此时要做什么。

Answer 1

您需要更改循环，使其具有退出条件，而不是使用 while (sc.hasNext()并在“问题” block 中添加一个条件来检查用户是否输入了 sQuit ，例如

boolean hasQuit = false;
do {
    f = sc.next(); // assigns the first standard input to f (can either be ? or quit)
    g = sc.next(); // assigns the second word from standard input to g (can either be perimeter or area)
    if (f.equals(sQues)) { // if first word is equal to "?" then the if statements continue
        if (g.equals(sQuit)) {
            hasQuit = true;
        } else if (g.equals(sPeri)) { // if the second word is equal to "perimeter" print out result
            //...
        } else if (g.equals(sArea)) { // if the second word is equal to "area" print out result
            //...
        }
    }
} while (!hasQuit);