Java超類繼承

我有一個擴展到兩個子類（CircleFromSimpleGeometricObject和RectangleFromSimpleGeometricObject）的超類（SimpleGeometricObject），以及一個調用CircleFromSimpleGeometricObject和RectangleFromSimpleGeometricObject的類，名爲TestCircleRectangle。繼調試，爲子類CircleFromSumpleGeometricObject，這行代碼：Java超類繼承

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

莫名其妙地調用超SimpleGeometricObject：

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

我有點困惑如何發生以及爲什麼有人可以幫助我理解爲什麼發生這種情況以下是所有課程的代碼。

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()); 
} 

}

來源

2013-07-09 Minh Tran

我將簡化那些名字;好名字很重要。我不明白爲什麼Circle，Rectangle和AbstractShape不足夠。 – duffymo

默認情況下，子類調用超類構造函數。你可以通過調用super –

像public CircleFromSimpleGeometricObject(double radius)構造函數總是必須包括它的父類的構造函數作爲第一線的呼叫;如果你沒有明確地做，編譯器會無形的插入一個對超類的無參數構造函數的調用，如果有的話。這就是發生在這裏的事情;構造函數自動調用public SimpleGeometricObject()。

構造函數可以調用父類的構造是這樣的：