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Thread: Little help with "extends" please

  1. #1
    Junior Member uzisuicide's Avatar
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    Default Little help with "extends" please

    I have to extend a class from squareDemo in this assignment. All i need to do is add depth to the compute surface area arithmetic. It wont allow me to print in the extended class. I also cant grab height, width from the parent class which I "thought" was the purpose of inheritance. Please help with code and explain how my logic is flawed. I'm a new programmer so please go easy on me heh...

    package square;
     
    /**
     *
     * @author Michael
     * Chapter 9 exercise 2
     */
    public class SquareDemo
    {
        public static void main(String[] args)
        {
            int height = 6;
            int width = 6;
            int surfaceAreaSQ = height * width;
     
            System.out.println("The surface area of the square is: " + surfaceAreaSQ);
        }
     
        public class CubeDemo extends SquareDemo
        {
            int height = 6;
            int width = 6;
            int depth = 6;
            int surfaceAreaCU = height * width * depth;
     
            System.out.println("The surface area of the cube is: " + surfaceAreaCU);
     
     
        }
     
    }
    Last edited by Json; April 27th, 2010 at 09:43 AM. Reason: Please use code tags.


  2. #2
    Super Moderator Json's Avatar
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    Default Re: Little help with "extends" please

    Hello there,

    The problem you have is that you've not actually declared any instance members in the SquareDemo class, therefore your CubeDemo will not be able to see any.

    You also need to take into account the access modifiers, if you mark members as private thats what they will be. If you want an inheriting class to have direct access to the superclass members you need to make the members protected.

    If you had protected instance members in the SquareDemo class your CubeDemo class would then be able to see them.

    I will see if I can dig up some sort of inheritance snippet, we should have something available.

    // Json

  3. #3
    Junior Member uzisuicide's Avatar
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    Default Re: Little help with "extends" please

    Okay scratch the last code. This code actually looks like it's going to work. I'm getting one error in the main. non-static variable cannot be used in static context. It's odd because the few lines above the error is basically doing the same thing without error. Check this out please.
    /**
     *
     * @author Michael Bowers
     * Chapter 9 - Assignment 2
     */
    public class Square
    {
        int height;
        int width;
        int surfaceArea;
     
    //********** CONSTRUCTOR Square **********
        public Square(int h, int w)
        {
            height = h;
            width = w;
        }//___________ END Constructor ________
     
        public void DisplaySquare()
        {
            System.out.println("The surface area of the square is: " + surfaceArea);
        }
     
        public void computeSurfaceArea()
        {
           surfaceArea = height*width;
        }
     
    //********** Extends Square **********
        public class Cube extends Square
        {
            int depth;
     
     //********** CONSTRUCTOR Cube **********       
            public Cube( int h, int w, int d)
            {
              super(h, w);
              depth = d;
            }//_______ END Constructor _______
     
            public void computeSurfaceArea()
            {
                super.computeSurfaceArea();
                surfaceArea = surfaceArea * depth;
            }
     
        }//_____ END Class Cube ______
     
        public void DisplayCube()
        {
            System.out.println("The surface area of the cube is: " + surfaceArea);
        }
     
     
        public static void main(String[] args)
        {
            Square square1 = new Square(6, 6);
            square1.computeSurfaceArea();
            square1.DisplaySquare();
     
            Cube cube1 = new Cube(6, 6, 6);
            cube1.computeSurfaceArea();
            cube1.DisplayCube();
        }
     
    }
    Last edited by helloworld922; April 28th, 2010 at 09:32 PM.

  4. #4
    Junior Member uzisuicide's Avatar
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    Default Re: Little help with "extends" please

    Fixed - disregard

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    Super Moderator helloworld922's Avatar
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    Default Re: Little help with "extends" please

    please surround your code with [code] tags please

    Also, if your problem is solved please mark the thread as [solved]

  6. #6
    Junior Member uzisuicide's Avatar
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    Default Re: Little help with "extends" please

    if (problem == solved)
         select Solved;
    else
         don't;
     
    // I don't know where the solved button resides.
    Fear is the mind killer.

  7. #7
    mmm.. coffee JavaPF's Avatar
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    Default Re: Little help with "extends" please

    Quote Originally Posted by uzisuicide View Post
    if (problem == solved)
         select Solved;
    else
         don't;
     
    // I don't know where the solved button resides.
    The 'Mark Thread As Solved' button is in Thread Tools at the top of the forums.

    I have done it for you this time
    Please use [highlight=Java] code [/highlight] tags when posting your code.
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