从实现的类向数组添加对象

Question

Good morning, my apologies if this question is complex/confusing. I am in an intro java course and I am having some difficulties with one of my assignments! You guys on here seem to have an answer for everything so I know you can help!

This assignment is to create specifications for some shapes (rectangles and triangles), but it must be implemeneted as such:

All shapes must implement a calculated interface which calculates their area/perimeter. A shapemanger class stores the calculated shapes in an array capable of storing up to 10 objects...

public class App
{
    public static void main(String[] args)
    {

        ShapeManager sm      =    new ShapeManager();

        Rectangle       r1  =   new Rectangle(100,120,10,13);
        sm.addShape(r1);

        sm.dump();
      }
}

public interface Calculated
{
     public double calculateArea();

     public double calculatePerimeter();

     public void dump();
}

public class Rectangle implements Calculated
{
    private int xCoord, yCoord, length, width, rectangleArea, rectanglePerimeter;
    public Calculated rectangleShape;

    public Rectangle(int XCoord, int YCoord, int Length, int Width)
    {
        XCoord = xCoord;
        YCoord = yCoord;
        Length = length;
        Width = width;
    }

    public double calculateArea()
    {
        rectangleArea = length * width;
        return rectangleArea;
    }

    public double calculatePerimeter()
    {
        rectanglePerimeter = (length *2) + (width * 2);
        return rectanglePerimeter;
    }

    public void dump()
    {
        System.out.println("The Area of the rectangle = " + rectangleArea);
        System.out.println("The Perimeter of the rectangle =" + rectanglePerimeter);
    }

}


public class ShapeManager
{
    private Calculated[] calcArray;
    private Calculated rectangle;
    public Calculated shape;

    public ShapeManager()
    {
        calcArray = new Calculated[10];
    }

    public void addShape(Calculated s)
    {
        int address = 0;
        while (calcArray[address] != null)
        {
            address++;
        }

        calcArray[address] = s;
    }

    public void dump()
    {
        for (int x = 0; x <= 9; x++)
        {

            if (calcArray[x] !=null)
            {
                calcArray[x].dump();
            }
        }
    }
    }

Currently my output is:

The Area of the rectangle = 0 The Perimeter of the rectangle =0

I am really stuck on what I am doing wrong, and why the output isnt calculated properly. Any assistance on this is really appreciated, thank you very much for your help and your patience!

Allyso

Answer 1

Change your dump method to:

public void dump()
{
    System.out.println("The Area of the rectangle = " + calculateArea());
    System.out.println("The Perimeter of the rectangle =" + calculatePerimeter());
}

You can improve it further by removing the two fields: rectangleArea and rectanglePerimeter and make the calculate functions like this:

public double calculateArea()
{  
    return length * width;
}

Now you save some memory as well. I would then rename the methods to getArea and getPerimeter .

Answer 2

You design needs some pruning of poor design choices, like caching the area etc:

public interface Shape {
    public double getArea();
    public double getPerimeter();
    public void dump();
}

public class Rectangle implements Shape {
    private int xCoord, yCoord, length, width;

    public Rectangle(int XCoord, int YCoord, int Length, int Width) {
        XCoord = xCoord;
        YCoord = yCoord;
        Length = length;
        Width = width;
    }

    public double getArea() {
        return length * width;
    }

    public double getPerimeter() {
        return (length + width) * 2;
    }

    public void dump() {
        System.out.println("The Area of the rectangle = " + getArea());
        System.out.println("The Perimeter of the rectangle =" + getPerimeter());
    }
}

Answer 3

Replace the function 'dump' in 'Rectangle' class as below:

public void dump()
{
    this.calculateArea();
    this.calculatePerimeter();
    System.out.println("The Area of the rectangle = " + rectangleArea);
    System.out.println("The Perimeter of the rectangle =" + rectanglePerimeter);
}

You could also do it in the loop inside 'dump' function in ShapeManager.