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POJava superclass inheritance
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copied!<p>I have a superclass (SimpleGeometricObject) which is extended to two subclasses (CircleFromSimpleGeometricObject and RectangleFromSimpleGeometricObject), and a class that invokes CircleFromSimpleGeometricObject and RectangleFromSimpleGeometricObject called TestCircleRectangle. Following the debugger, for subclass CircleFromSumpleGeometricObject, this line of code: </p> <pre><code>public CircleFromSimpleGeometricObject(double radius){ this.radius = radius; } </code></pre> <p>somehow invokes the superclass SimpleGeometricObject: </p> <pre><code> /** Construct a default geometric object */ public SimpleGeometricObject() { dateCreated = new java.util.Date(); } </code></pre> <p>I am a bit confused about how this happens and why, can someone help me understand why this happens? Below are the codes to all the classes.</p> <pre><code>public class SimpleGeometricObject { private String color = "white"; private boolean filled; private java.util.Date dateCreated; /** Construct a default geometric object */ public SimpleGeometricObject() { dateCreated = new java.util.Date(); } /** Construct a geometric object with the specified color * and filled value */ public SimpleGeometricObject(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, its 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; } /** Return a string representation of this object */ public String toString() { return "created on " + dateCreated + "\ncolor: " + color + " and filled: " + filled; } } public class CircleFromSimpleGeometricObject extends SimpleGeometricObject { private double radius; public CircleFromSimpleGeometricObject() { } public CircleFromSimpleGeometricObject(double radius){ this.radius = radius; } public CircleFromSimpleGeometricObject(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; } /** Return area */ public double getArea() { return radius * radius * Math.PI; } /** Return diameter */ public double getDiameter() { return 2 * radius; } /** Return perimeter */ public double getPerimeter() { return 2 * radius * Math.PI; } /** Print the circle info */ public void printCircle() { System.out.println("The circle is created " + getDateCreated() + " and the radius is " + radius); } } public class RectangleFromSimpleGeometricObject extends SimpleGeometricObject { private double width; private double height; public RectangleFromSimpleGeometricObject() { } public RectangleFromSimpleGeometricObject( double width, double height) { this.width = width; this.height = height; } public RectangleFromSimpleGeometricObject( 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; } /** Return area */ public double getArea() { return width * height; } /** Return perimeter */ public double getPerimeter() { return 2 * (width * height); } } public class TestCircleRectangle { public static void main(String[] args) { CircleFromSimpleGeometricObject circle = new CircleFromSimpleGeometricObject(1); System.out.println("A circle " + circle.toString()); System.out.println("The color is " + circle.getColor()); System.out.println("The radius is " + circle.getRadius()); System.out.println("The area is " + circle.getArea()); System.out.println("The diamter is " + circle.getDiameter()); RectangleFromSimpleGeometricObject rectangle = new RectangleFromSimpleGeometricObject(2, 4); System.out.println("\nA rectangle " + rectangle.toString()); System.out.println("The area is " + rectangle.getArea()); System.out.println("The perimeter is " + rectangle.getPerimeter()); } } </code></pre>

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