我有一个超类（SimpleGeometricObject），它扩展到两个子类（CircleFromSimpleGeometricObject 和 RectangleFromSimpleGeometricObject），还有一个调用 CircleFromSimpleGeometricObject 和 RectangleFromSimpleGeometricObject 的类，称为 TestCircleRectangle。在调试器之后，对于子类 CircleFromSumpleGeometricObject，这行代码：
public CircleFromSimpleGeometricObject(double radius){
this.radius = radius;
}
以某种方式调用超类 SimpleGeometricObject：
/** Construct a default geometric object */
public SimpleGeometricObject() {
dateCreated = new java.util.Date();
}
我对这是如何发生的以及为什么会发生有些困惑，有人可以帮我理解为什么会发生这种情况吗？以下是所有类的代码。
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());
}
}