Question

public class Fan {
        public static void main(String[] args){
Fan fan1 = new Fan();
        fan1.setSpeed(FAST);
        fan1.setRadius(10);
        fan1.setColor("yellow");
        fan1.setOn(true);
        System.out.println(fan1.toString());        
    }

    // fan speed variables
    final static int SLOW = 1;
    final static int MEDIUM = 2;
    final static int FAST = 3;

    // Other fan variables
    private int speed;
    private boolean on; // true means on
    private double radius;  // radius of fan
    String color;

    // No-arg constructor
    public void Fan(){
        speed = SLOW;
        on = false;
        radius = 5;
        color = "blue";
    }

    // Mutator methods
    public void setSpeed(int newSpeed){
        if(newSpeed < 0)
            System.out.println("Illegal speed!");
        else
            speed = newSpeed;
    }

    public void setOn(boolean newOn){
         on = newOn;
    }

    public void setRadius(int newRadius){
        if(newRadius < 0)
            System.out.println("Illegal radius!");
        else 
            radius = newRadius;
    }

    public void setColor(String newColor){
        color = newColor;
    }

    // Accessor methods
    public int getSpeed(){
        return speed;
    }

    public boolean getOn(){
        return on;
    }

    public double getRadius(){
        return radius;
    }

    public String getColor(){
        return color;
    }

    // toString method to output Fan data
    public String toString(){
        if(on = false)
            return "Fan is off.";
        else
            return "Fan Properties:\n" + "Fan speed: " + speed + "\n"
            + "Color: " + color + "\n"
            + "Radius: " + radius + "\n";
    }
}

The above piece of code is simple but I was wondering how the toString method uses the on variable even though I didn’t supply parameters for that method. Also, why do we not need to invoke get methods in the main class and only need to invoke the set methods? (please explain how each method invokes one another until the final output)

Thanks a lot!

Answer 1

As far as you are in this class body you can access everything (except for static can not access non-static). That means that you can easily set and get variables like that:

var = <value>;
System.out.println(var);

However nobody stops you from using the accessor methods – getter and setters. It is just not required.

One final note:

if(on = false)

This will always fail – it does assignment to false and then checks the newly assigned value (which is false). You need to check for equality here. Like that:

if(on == false)

Or even better:

if(!on)