CODEWITHSUNDEEP
javavariablessubclasssuperclass
JavaPeasant
JavaPeasant

Reputation: 41

Cannot find variable from subclass in main class

I am trying to use the Volume method from my sub class in my testing class super class by using v.Volume(volume); but it is saying it can't find the symbol volume. I am setting the radius in the testing class, and it is supposed to output the volume from it. I feel like I am over looking something very obvious. I know that it is trying to use a variable named volume from the super class but I am not sure what to put.

testing class code

//balloon testing
    Balloon r = new Balloon();
    Balloon v = new Balloon();

    System.out.println("Radius " + r.getRadius());
    System.out.println("Volume " + v.getVolume());

    r.inflate(5);
    v.Volume(volume);

    System.out.println("Radius " + r.getRadius());
    System.out.println("Volume " + r.getVolume());

sub class code

public class Balloon {
//declare
public double radius;
public double volume;

//constructor
public Balloon(){
    radius = 0;
    volume = 0;
}

//setters
public void inflate(double r){
    radius = r;
}

//accessors
public double getRadius(){
    return radius;
}

public double getVolume(){
    return volume;
}

public void Volume(double volume){
    volume = ((4/3)* Math.PI * (radius*radius*radius));
}

}

Upvotes: 0

Views: 186

Answers (2)

Jeremy Barnes
Jeremy Barnes

Reputation: 677

Its not clear what you're asking here, but I'll try to answer anyways.

You don't have a subclass or a superclass here, those are very specific terms which you are welcome to read more about.

To your question, though, I think your problem is that in your Volume method you pass in a parameter (volume) which you do not use at all. Instead, you set a member variable (Balloon.volume) based on the radius. Balloon.volume is very different from the parameter double volume that is passed. I have annotated your classes to try to clarify what's going on here.

public class Balloon {
    //declare
    public double radius; //this is the member variable which is a property of each member of the Balloon class. I refer to it above as Balloon.volume
    public double volume;

    public Balloon(){
        radius = 0;
        volume = 0;
    }

    public void inflate(double r){
        radius = r;
    }


    public double getRadius(){
        return radius;
    }

    public double getVolume(){
        return volume;
    }

    public void Volume(double volume){ //this is an external, unused parameter
        volume = ((4/3)* Math.PI * (radius*radius*radius)); //this sets Balloon.volume and ignores the parameter volume
    }

}

Perhaps it would be clearer what was going on if you renamed your variables:

    public void Volume(double someOtherVolume){ //this is an external, unused parameter
        volume = ((4/3)* Math.PI * (radius*radius*radius)); //this sets Balloon.volume and ignores the parameter volume
    }

This should make it clear that the parameter and the member variable are different. Your symbol exception comes from this line:

v.Volume(volume);

The variable there in parens is never defined. You must first declare and define a variable before using it.

double volume = 8;

Since in your testing class you are outside the balloon class, you cannot simply refer to Balloon.volume. You must create a new variable.

Upvotes: 2

waxtah
waxtah

Reputation: 306

change Volume method body to (and rename it):

public void calculateVolume(){
    volume = ((4/3)* Math.PI * (radius*radius*radius));
}

and before invoke this method - set radius value by setter.

Upvotes: 1

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