(Sum the areas of geometric objects) Write a method that sums the areas of all the geometric objects in an array. The method signature is

/*********************************************************************************
* (Sum the areas of geometric objects) Write a method that sums the areas of all *
* the geometric objects in an array. The method signature is:                    *
*                                                                                *
* public static double sumArea(GeometricObject[] a)                              *
*                                                                                *
* Write a test program that creates an array of four objects (two circles and    *
* two rectangles) and computes their total area using the sumArea method.        *
*********************************************************************************/
public class Exercise_13_12 {
	/** Method main */
	public static void main(String[] args) {
		// Create an array of four objects
		GeometricObject[] array = {new Circle(5), new Circle(8),
			new Rectangle(3, 4), new Rectangle(4, 2)};

		// Display results
		System.out.println("Total area of elements in array: " + sumArea(array));
	}

	/** Returns the sum of the areas of all 
	 *  the geometric objects in an array */
	public static double sumArea(GeometricObject[] a) {
		double sum = 0;
		for (int i = 0; i < a.length; i++) {
			sum += a[i].getArea();
		}
		return sum;
	}
}

Circle.java

public class Circle
		extends GeometricObject implements Comparable<Circle> {
	private double radius;

	public Circle() {
	}

	public Circle(double radius) {
		this.radius = radius;
	}

	public Circle(double radius, 
		String color, boolean filled) {
		this.radius = radius;
		setColor(color);
		setFilled(filled);
	}

	/** Return radius */
	public double getRadius() {
		return radius;
	}

	/** Set a new radius */
	public void setRadius(double radius) {
		this.radius = radius;
	}

	@Override /** Return area */
	public double getArea() {
		return radius * radius * Math.PI;
	}

	/** Return diameter */
	public double getDiameter() {
		return 2 * radius;
	}

	@Override /** Return perimeter */
	public double getPerimeter() {
		return 2 * radius * Math.PI;
	}

	@Override /** Return true if objects radii are the same */
	public boolean equals(Object o) {
		return this.compareTo((Circle)o) == 0;
	}

	@Override /** Implement compareTo method */
	public int compareTo(Circle o) {
		if (this.radius > o.radius)
			return 1;
		else if (this.radius < o.radius)
			return -1;
		else
			return 0;
	}

	@Override /** Implement the toString method in GeometricObject */
	public String toString() {
		return super.toString() + "\nDate created: " + getDateCreated() +
			"\nRadius: " + radius;
	}
}

GeometricObject.java 

public abstract class GeometricObject {
	private String color = "while";
	private boolean filled;
	private java.util.Date dateCreated;

	/** Construct a default geometric object */
	protected GeometricObject() {
		dateCreated = new java.util.Date();
	}

	/** Construct a geometric object with color and filled value */
	protected GeometricObject(String color, boolean filled) {
		dateCreated = new java.util.Date();
		this.color = color;
		this.filled = filled;
	}

	/** Return color */
	public String getColor() {
		return color;
	}

	/** Set a new color */
	public void setColor(String color) {
		this.color = color;
	}

	/** Return filled. Since filled is boolean,
	 *  the get method is named isFilled */
	public boolean isFilled() {
		return filled;
	}

	/** Set a new filled */
	public void setFilled(boolean filled) {
		this.filled = filled;
	}

	/** Get dateCreated */
	public java.util.Date getDateCreated() {
		return dateCreated;
	}

	@Override
	public String toString() {
		return "created on " + dateCreated + "\ncolor: " + color +
			" and filled: " + filled;
	}

	/** Abstract method getArea */
	public abstract double getArea();

	/** Abstract method getPerimeter */
	public abstract double getPerimeter();

}

Rectangle.java

public class Rectangle
		extends GeometricObject implements Comparable<Rectangle> {
	private double width;
	private double height;

	public Rectangle() {
	}

	public Rectangle(
		double width, double height) {
		this.width = width;
		this.height = height;
	}

	public Rectangle(
		double width, double height, String color, boolean filled) {
		this.width = width;
		this.height = height;
		setColor(color);
		setFilled(filled);
	}

	/** Return width */
	public double getWidth() {
		return width;
	}

	/** Set a new width */
	public void setWidth(double width) {
		this. width = width;
	}

	/** Return height */
	public double getheight() {
		return height;
	}

	/** Set a new height */
	public void setheight(double height) {
		this.height = height;
	}

	@Override /** Return area */
	public double getArea() {
		return width * height;
	}

	@Override /** Return perimeter */
	public double getPerimeter() {
		return 2 * (width * height);
	}

	@Override /** Implement compareTo method */
	public int compareTo(Rectangle o) {
		if (getArea() > o.getArea())
			return 1;
		else if (getArea() < o.getArea())
			return -1;
		else
			return 0;
	}

	@Override /** Return true if both objects are equal */
	public boolean equals(Object o) {
		return this.compareTo((Rectangle)o) == 0;
	}

	@Override /** Return String discription of this rectangle */
	public String toString() {
		return super.toString() + "\nWidth: " + width + "\nHeight: " + height
			+ "\nArea: " + getArea() + "\nPerimeter: " + getPerimeter();
	}
}