In this assigment you will write an object oriented program using Java that will consist of a class hierarchy of shapes (e.g., square, triangle, circle) that implement a shape interface.  The shape interface requires that a shape provides instance methods to reveal its name, and its perimeter and area measurements.

To be handed in:  a diskette labeled with your name, containing the subdirectories comprising your JBuilder project subtree (your .jpr project file should be in the root of the subtree) and printouts of your Java source files (*.java).  Please place your diskette and printouts in a large envelope also labeled with your name.

The project will consist of the following interface and classes:

• Interface name:

Shape

• Instance attributes:
 
by definition, interfaces don't have instance attributes

• Constructor:
 
by definition, interfaces don't have constructors

• Instance methods:

String name()

    returns the name of the shape (e.g., "Triangle")

double area()

    returns the area measurement of the shape

double perimeter()

    returns the perimeter measurement of the shape

• Abstract class name:
 
AbstractShape implements Shape
• Instance attributes:
 
none
• Constructor:
 
none
• Instance methods:
 
//must have these, since this class implements Shape interface;
//but leave abstract...
abstract String name();
abstract double area();
abstract double perimeter();

//Using methods from Shape interface, override toString() method

//--that's the whole reason for this abstract class!
String toString()
returns a reference to an object of class String that contains a string representation of what the shape looks like, e.g., "Rectangle with perimeter 14 and area 12" -- this method should use the Shape interface methods to construct such a string...

• Class name:

Circle extends AbstractShape  // inherits from abstract class AbstractShape

• Instance attributes:
 
double radius;  // the length of the circle's radius

• Constructor:
 
Circle(double r)
            constructs a new Circle object with the specified radius
        Sample invocation:
            Circle aCircle = new Circle(3.0);

• Instance methods:
 
must implement the three methods left abstract by abstract class AbstractShape.  Recall the formulae to calculate the area and circumference of a circle (where an approximation of pi is available from Math.PI):
area = pi * r * r
circumference = 2 * pi * r

• Class name:
 
Triangle extends AbstractShape  // inherits from abstract class AbstractShape
• Instance attributes:
 
double sideA, sideB, sideC;  // the lengths of the three sides of the triangle
• Constructor:
 
Triangle(double a, double b, double c)
   constructs a new Triangle object with the three specified side lengths
Sample invocation:
   Triangle aTriangle = new Triangle(3.0, 4.0, 5.0);

• Instance methods:
 
must implement the three methods left abstract by abstract class AbstractShape.  Use Heron's formula to calculate the area of a triangle given the lengths of its three sides:
   area = Math.sqrt( s * (s - sideA) * (s - sideB) * (s - sideC) ),
where
   s = (sideA + sideB + sideC) / 2

• Abstract class name:
 
AbstractRectangle extends AbstractShape  // inherits from abstract class AbstractShape
• Instance attributes:
 
double length, width;  // the length and width of a rectangle
• Constructor:
 
by definition, abstract classes don't have constructors
• Instance methods:
 
must implement the three methods left abstract by abstract class AbstractShape.  Recall the formulae to calculate the area and perimeter of a rectangle:
 
area = length * width
perimeter = (2 * length) + (2 * width)

• Class name:
 
MyRectangle extends AbstractRectangle
• Instance attributes:
 
// inherited from AbstractRectangle
• Constructor:
 
// constructor takes two parameters to initialize
// corresponding inherited instance attributes
MyRectangle(double l, double w)
Sample invocation:
MyRectangle aRectangle = new MyRectangle(4.0, 6.0);

• Instance methods:
 
// inherits area and perimeter instance methods from abstract class AbstractRectangle
// overload the interface method for shape name to return string "Rectangle"
String name();

• Class name:
 
Square extends AbstractRectangle
• Instance attributes:
 
// inherited from AbstractRectangle
• Constructor:

// constructor takes one parameter (length) with
// which to initialize both inherited instance attributes
Square(double l)
Sample invocation:
Square aSquare = new Square(5.0);

• Instance methods:

 
// inherits area and perimeter instance methods from abstract class AbstractRectangle
// overload the interface method for shape name to return string "Square"
String name();

• Class name:
 
ShapeApplet extends JApplet  // once again, your user interface Is-a JApplet!
• Instance attributes:
 
Vector shapes;  // a collection of shapes
Notice how your ShapeApplet JApplet uses (contains) shape objects instantiated from the previous classes.

• Instance methods:
 
You'll define methods corresponding to the instances of JButtons on your JApplet panel.  The buttons will add circles, triangles, rectangles, and squares to the shapes vector.  The parameters
for these new shapes will be taken from the corresponding JTextFields on the applet panel.  Similar to the previous programming assignment, you'll need to parse the double values from the strings returned by getText().

You'll find the following static (class) method helpful:
     Double.parseDouble(s) -- returns a double value parsed from its String parameter.
 

A "List Shapes" button will use an object of class Iterator to iterate through the shapes vector, and use System.out.println() to list the stored shapes.

Unlike the previous assignment, the objects stored in the shapes vector can be instances of different shape classes -- but all the shape classes extend class AbstractShape, which implements the Shape interface.  Since AbstractShape overrides the toString() method for shape objects, we can cast references from our iterator's .next() method to be (AbstractShape) references, and printing our shapes is as simple as:  System.out.println( aShape );  !!!

The output from the System.out.println()'s should look something like this:

Shape Rectangle with area = 20.0 and perimeter = 18.0
Shape Square with area = 36.0 and perimeter = 24.0
Shape Triangle with area = 6.0 and perimeter = 12.0
Shape Circle with area = 113.09733552923255 and perimeter = 37.69911184307752