理解嵌套循环和类

Question

我开始了一个项目来理解深度嵌套的循环和类。在我的 CYCLING 方法中，当我到达 if(y >= 0) 循环时，它没有在类中正确使用我的变量。例如，如果 MPH 是 15 并且档位是 1 或 3，它不会要求我换档。或者如果档位为 1 且速度为 11+，它不会要求我换档？我做错了什么？

---

public class Bike {
    int speed;
    int gear;

    void changeGear(int newVal) {
        gear = newVal;
    }

    void speedUp(int newVal) {
        speed = newVal;
    }

    void breaks(int slow) {
        speed = speed + slow;
    }

    void printState() {
        System.out.println("Gear is: " + gear);
        System.out.println("Speed is: " + speed + ("MPH"));
    }
}

//________________________

public static boolean cycle = true;
public static Bike b1 = new Bike();
public static int x;
public static int y;
public static Scanner input = new Scanner(System.in);
public static int choice;

//______________________________

public static void cycling() {
    while (cycle == true) {
        System.out.println("What would you like to do now? Enter a number.");
        System.out.println("1: Speed Change");
        System.out.println("2: Change Gear");
        choice = input.nextInt();
        if (choice == 1) {
            System.out.println("Choose a speed change");
            y = input.nextInt();
            if (y < 0) {
                b1.breaks(y);
                if (b1.speed < 0) {
                    b1.speed = Math.abs(y) + y;
                    System.out.println("You've stopped entirely");
                }
            }
            if (y >= 0) {
                b1.speed = y;
                b1.printState();
                if (b1.speed >= 0 && b1.speed <= 10) {
                    while (b1.gear != 1) {
                        System.out.println("You need to be in Gear 1 for " + "that! Please change gears.");
                        x = input.nextInt();
                        b1.changeGear(x);
                    }
                    if (b1.speed >= 11 && b1.speed <= 20) {
                        while (b1.gear != 2) {
                            System.out.println("You need to be in Gear 2 for" + "that! Please change gears.");
                            x = input.nextInt();
                            b1.changeGear(x);
                        }
                        if (b1.speed >= 21) {
                            while (b1.gear != 3) {
                                System.out.println("You need to be in Gear 3 for" + "that! Please change gears.");
                                x = input.nextInt();
                                b1.changeGear(x);
                            }
                        }
             /*if(b1.speed >= 0 && b1.speed <=10){
                 b1.gear = 1;
             }else if(b1.speed >= 11 && b1.speed <=20){
                 b1.gear = 2;
             }else if(b1.speed >= 21){
                 b1.gear = 3;
             }*/
                        b1.printState();
                    }
                }
            }
        }
    }
}

Answer 1

想想你的陈述。你有一些基本上看起来像这样的东西：

if (b1.speed >= 0 && b1.speed <= 10) {
    //some while loop here to do whatever
    if (b1.speed >= 11 && b1.speed <= 20) {
        //more code
    }
}

在您的代码中，此语句永远不会为真：

if (b1.speed >= 11 && b1.speed <= 20) {

获得该语句的唯一方法是 b1.speed>=0 && b1.speed<=10。因此，当您到达第二个（嵌套）if 语句时， b1.speed 会在 11 到 20 之间吗？