多态，继承

Question

So I've copied the MountainBike, RoadBike, TestBikes class from Java's tutorials ( http://docs.oracle.com/javase/tutorial/java/IandI/polymorphism.html ).

I then made "Bicycle.java".. But if I try to make it execute by making it the main class, then it won't even compile (tons of illegal start of expressions.)

Is there anyway to make this compile along with all of the classes that inherit properties from this class?

   public class Bicycle {
    public static void main(String[] args) {
        int cadence;
       int gear;
        int speed;

    public Bicycle(int startCadence, int startSpeed, int startGear) {
        gear = startGear;
        cadence = startCadence;
        speed = startSpeed;
    }


    public void setCadence(int newValue) {
        cadence = newValue;
    }

    public void setGear(int newValue) {
        gear = newValue;
    }

    public void applyBrake(int decrement) {
        speed -= decrement;
    }

    public void speedUp(int increment) {
        speed += increment;
    }

    public void printDescription() {
    System.out.println("\nBike is " + "in gear " + this.gear
        + " with a cadence of " + this.cadence +
        " and travelling at a speed of " + this.speed + ". ");
    }
}
}

Answer 1

You're putting methods inside of methods and in fact you've got your main method enclosing all of the code of your Bicycle class -- don't do this. Your main method should be its own separate method, should not hold other methods, should create a Bicycle instance. call methods on this instance and that's about it.

public class Bicycle {
        public int cadence;
        public int gear;
        public int speed;

    public Bicycle(int startCadence, int startSpeed, int startGear) {
        gear = startGear;
        cadence = startCadence;
        speed = startSpeed;
    }


    public void setCadence(int newValue) {
        cadence = newValue;
    }

    public void setGear(int newValue) {
        gear = newValue;
    }

    public void applyBrake(int decrement) {
        speed -= decrement;
    }

    public void speedUp(int increment) {
        speed += increment;
    }

    public void printDescription() {
    System.out.println("\nBike is " + "in gear " + this.gear
        + " with a cadence of " + this.cadence +
        " and travelling at a speed of " + this.speed + ". ");
    }

    public static void main(String[] args) {
      Bicycle bicycle = new Bicycle(20, 10, 2);
      System.out.println(bicycle);
      // ... etc
    }
}

Next time, please show us the actual code that is causing the problem from the get-go as well as your error messages. You'll get much better help this way, and we'll all be a little less frustrated.

Answer 2

Take in the previous answers and start over, try breaking up the different methods and debugging each instead of getting a wash of errors and tossing up your hands. Make sure each compiles as you code so you know where the problems begin.