Inheritance and Subclasses

[ashlan cooper]

Hello there,
I am trying to solve this exercise I am doing.
Basically I need to create a ,

Vehicle

class ( I already did) that has 3 instance variables (

 double horsepower, aerodynamics, weight

)
In this class as well I did the following

public class Vehicle
{
    private double horsepower, aerodynamics, weight;

    public Vehicle(double initialHorsepower, double initialAerodynamics, double initialWeight)
    {
        // initialise instance variables
        horsepower = initialHorsepower;
        aerodynamics = initialAerodynamics;
        weight = initialWeight;
    }
    
    public double getHorsepower()
    {
        return horsepower;
    }
    
    public double getAerodynamics()
    {
        return aerodynamics;
    }   
    
    public double getWeight()
    {
        return weight;
    }
    

}

Then I created a subclass of Vehicle called SportCar (I extended the class)
it has an additional variable in it )

 double topspeed 

All sportcars have aerodynamics = 0.5

public class SportCar extends Vehicle
{
    public double topspeed;

    public SportCar(double initialHorsepower, double initialAerodynamics, double initialWeight)
    {
       super(initialHorsepower);
       super(initialAerodynamics);
       super(initialWeight);
    }
    
    public double getTopspeed()
    {
        return topspeed;
    }

}

I need to create 3 sportcars which have the following:
SportCar1 : horsepower = 200, weight = 1500, topspeed = 220
SportCar2 : horsepower = 100, weight = 1000, topspeed = 170
SportCar3 : horsepower = 135, weight = 1100.2, topspeed = 173

So I created them in another class called TestConsumption

public class TestConsumption
{
   
    public static void main(String[] args)
    {
        SportCar SportCar1 = new SportCar();
        SportCar SportCar2 = new SportCar();
        SportCar SportCar3 = new SportCar();
        
        SportCar.getAerodynamics(0.5);
    }

}

my problems are:
How do I create 3 instances of sportcar/initialize the horsepowers, weights and topspeeds for all the sportcars?

Is my method of setting aerodynamic =0.5 for all sportcars right?

Are those codes correct. I did get a few cannot find symbol along the way.


Any help is greatly appreciated.

[Mohamed Sanaulla]

Your Super class- Vehicle has the constructor which takes- three parameters. But in the sub class constructor- SportsCar you are calling super(<parameter>), but as you would see- the Vehicle would be expecting: super(param1,param2,param3).

Java provides a default- no-arg constructor if the constructor is not overloaded in the class. But if the constructor is overloaded- the programmer would have to specify the no-arg constructor- something like:

class SubClass extends SuperClass
{
    public SubClass()
    {
       //No Arg constructor
    }
    public SubClass(param1,param2,param3)
    {
       //Overloaded constructor
    }
}

Now coming to initializing the fields for the class- You can pass it in the constructor- while creating the instance or use the setters to set those values.

If you want to set a particular value for a particular variable for all the instances of the class- You would have to declare the variable/field as Static- Something like

class SubClass extends SuperClass
{
     public static MY_COMMON_VARIABLE=someValue;
}

[ashlan cooper]

Thank you, will try my best to change accordingly

[Campbell Ritchie]

You should be writing

 . . . 
public SportsCar(double horsepower, double aerodynamics, double weight, double topSpeed)
{
   super(horsepower, aerodynamics, weight);
   this.topSpeed = topSpeed;
}

You are allowed to write super(...) or this(...) in the constructor, but only as the very first statement. So you can't get both in, and you can't use them twice.

[Rob Spoor]

Actually, if all sports cars have an aerodynamics value of 0.5, that should be

public static final double AERO_DYNAMICS = 0.5; // use a constant

public SportsCar(double horsepower, double weight, double topSpeed)
{
   super(horsepower, AERO_DYNAMICS, weight);
   this.topSpeed = topSpeed;
}

[Campbell Ritchie]

Rob Spoor wrote: . . . if all sports cars have an aerodynamics value of 0.5 . . .

I had missed that bit. Sorry.

[ashlan cooper]

Hey guys,
thanks. I modified the code

public class Vehicle
{
    // instance variables - replace the example below with your own
    private double horsepower, aerodynamics, weight;

    public Vehicle(double initialHorsepower, double initialAerodynamics, double initialWeight)
    {
        // initialise instance variables
        horsepower = initialHorsepower;
        aerodynamics = initialAerodynamics;
        weight = initialWeight;
    }
    
    public double getHorsepower()
    {
        return horsepower;
    }
    
    public void getAerodynamics(double setAerodynamics)
    {
        setAerodynamics = aerodynamics;
    }   
    
    public double getWeight()
    {
        return weight;
    }
    

}

public class SportCar extends Vehicle
{
   private double topSpeed;
   
   public SportCar(double initialHorsepower, double initialWeight, double topSpeed) 
   { 
      super(initialHorsepower, 0.5, initialWeight);
      this.topSpeed= topSpeed;
   
   }
    
    public double getTopspeed()
    {
        return topSpeed;
    }

}

public class TestConsumption
{
    public static void main(String[] args)
    {
        SportCar SportCar1 = new SportCar(200,1500,220);
        SportCar SportCar2 = new SportCar(100,1000,170);
        SportCar SportCar3 = new SportCar(135, 1100.2, 173);
     
    }

}

So what do you think?

and what I am trying to do now is that
I want to implement this formula for fuel consumption under the TestConsumption class
(1000+(weight/5))*(topspeed/100)*(aerodynamics*horsepower)/1000

for those 3 new sportcars I created.

How do I pass the values of each sportcar; sportcar1,2,3
into this formula

thanks

[Campbell Ritchie]

ashlan cooper wrote: . . .

public class Vehicle
{
    . . .
    
    public void getAerodynamics(double setAerodynamics)
    {
        setAerodynamics = aerodynamics;
    }   
    . . .
}

. . .

That method will most definitely not do what you want.