C++PKJava的动态绑定与静态绑定

banxi1988

在我前面的一篇文章中,有写到C++的静态绑定和动态绑定.期间遇到了很多问题.
而用Java的话,可以很轻松的实现所要的需求.
但是...
/** * @time 上午10:23:34 * @fileName TestStaticDynamicBinding.java * @package  me.banxi.oo */package me.banxi.oo;class Figure{public static final String name = "Figure";public Figure(){}public double area(){return 0.0;}}class Circle extends Figure{public static final String name = "Circle";private double _radius;public Circle() {}public Circle(double radius){_radius = radius;}public double area(){return Math.PI*_radius*_radius;}}class Rectangle extends Figure{public static final String name = "Rectangle";private double _length;private double _width;public Rectangle(){}public Rectangle(double length,double width){_length = length;_width = width;}public double area(){return _length*_width;}}/** * @author banxi1988 */public class TestStaticDynamicBinding {static void printArea(Figure figure){System.out.println(figure.name+"的面积是:"+figure.area());}public static void main(String[] args) {Figure figure = new Figure();printArea(figure);Circle circle = new Circle(2.0);printArea(circle);Rectangle rect = new Rectangle(3.0,4.0);printArea(rect);}}/** *banxi1988@banxi:~/cppworkspace/C++_pk_Java/bin$ java me.banxi.oo.TestStaticDynamicBindingFigure的面积是:0.0Figure的面积是:12.566370614359172Figure的面积是:12.0banxi1988@banxi:~/cppworkspace/C++_pk_Java/bin$  ***/
由此可见Java中类成员方法都是动态绑定的.
但是类中静态成员还是静态绑定的.
经过测试发现,对于类的中字段属性,也是静态绑定的..
所以就算我把name声明改成下面的,最后结果输出的还是Figure.
public  final String name = "Circle";

修改后如下,完成,静态绑定:
/** * @time 上午10:23:34 * @fileName TestStaticDynamicBinding.java * @package  me.banxi.oo */package me.banxi.oo;class Figure{private static final String name = "Figure";public Figure(){}public String getName(){return name;}public double area(){return 0.0;}}class Circle extends Figure{private static  final String name = "Circle";private double _radius;public Circle() {}public Circle(double radius){_radius = radius;}public String getName(){return name;}public double area(){return Math.PI*_radius*_radius;}}class Rectangle extends Figure{private static final String name = "Rectangle";private double _length;private double _width;public Rectangle(){}public Rectangle(double length,double width){_length = length;_width = width;}public String getName(){return name;}public double area(){return _length*_width;}}/** * @author banxi1988 */public class TestStaticDynamicBinding {static void printArea(Figure figure){System.out.println(figure.getName()+"的面积是:"+figure.area());}public static void main(String[] args) {Figure figure = new Figure();printArea(figure);Circle circle = new Circle(2.0);printArea(circle);Rectangle rect = new Rectangle(3.0,4.0);printArea(rect);}}/** *banxi1988@banxi:~/cppworkspace/C++_pk_Java/bin$ java me.banxi.oo.TestStaticDynamicBindingFigure的面积是:0.0Circle的面积是:12.566370614359172Rectangle的面积是:12.0banxi1988@banxi:~/cppworkspace/C++_pk_Java/bin$  ***/
下面测试一下Java中同类中构造函数的调用.
如下,将Rectangle类的name属性.写成下面的形式:
private static final String name;//errorprivate double _length;private double _width;public Rectangle(){name = "Rectangle";}public Rectangle(double length,double width){this();_length = length;_width = width;}public String getName(){return name;}
上面有一句语句是有错的,就是static final同时修改的字段.name没有直接初始化.
就违反了Java中上述两个修饰的属性了.
支持任意一个都可以.
修改后如下:
class Rectangle extends Figure{private  static String name;private double _length;private double _width;public Rectangle(){name = "Rectangle";}public Rectangle(double length,double width){this();_length = length;_width = width;}public String getName(){return name;}public double area(){return _length*_width;}}
总结Java中的方法是动态绑定的.而字段则是静态绑定.
在Java中可以直接对字段,进行初始化.
而C++中则静态属性字段要在类外部初始化.实例属性字段要在构造函数中初始化.
而且在C++中调用同一类中构造函数好像没有java中的this()机制.
如果在C++中直接调用另一个构造函数的话,生成了另一个隐藏的对象.