在 Java 中防止负数并返回以前的值？

Question

In setSpeed I am trying to have a validation check on numbers passed through. If a negative number is passed it should pass the initial value. (speed:0) but if I pass a 3 first then a negative number the value returned is 3. I for some reason can't get 0 returned if I pass a negative number first.

public class Conveyor {

    private String type;
    private double speed;

    public Conveyor(String t, double s) {
        type = t;
        speed = s;
        setSpeed(s);
    }

    public String getType() {
        return type;
    }

    public double getSpeed() {
        return speed;
    }

    public void setSpeed(double s) {

        if (s > 0) {
            speed = s;
        } else {
            speed = speed;
        }

    }

    public double timeToTransport(double distance) {
        distance = distance / speed;
        return distance;

    }

}

Answer 1

Take a look at your constructor:

    speed = s;
    setSpeed(s);

and your setter:

public void setSpeed(double s) {

    if (s > 0) {
        speed = s;
    } else {
        speed = speed;
    }
}

What happens when you put in a negative value is that it is set in the constructor and kept in the setter because of the speed = speed .

So just remove speed = s from the constructor and remove the else -section in the setter.