java中转型(upcasting)与动态绑定(dynamic binding)或者后期(late binding)细节

from: http://blog.csdn.net/kaiming2008/archive/2007/04/27/1587843.aspx
在Java中,父类与子类之间的类型转换有两种,一种是子类向上转型父类(这永远是安全的),另一种是父类向下转型为子类(这得由相应的instanceof来判断数据类型,同时这也是一种不安全的转换)

Base class 与derived
class 之间,为了达到从一个特定类型转为一个通用类型(有点多态的味道),可以借助向上]转型这一工具(即子类向上转为父类类型的),因为Java
里的对象引用都是dynamic binding或者lated bindin或者runing time
binding,缺点就是在向上转型的过程中会丢失了属于子类专用的方法
;向下转型中用得最多的就是interface的运用.

下面用一段代码讲示:

class Base

{

public void baseMethod()

{

System.out.println("into Base#baseMethod");

}

public void fuc()

{

System.out.println("into Base#fuc");

}

}

class Child extends Base

{

public void childMethod()

{

System.out.println("into Child#childMethod");

}

public void fuc()

{

System.out.println("into Child#fuc");

}

}

class CCChild extends Child

{

public void ccchildMethod()

{

System.out.println("into CCChild#ccchildMethod");

}

public void fuc()

{

System.out.println("into CCChild#fuc");

}

}

class DChild extends CCChild

{

public void dchildMethod()

{

System.out.println("into DChild#dchildMethod");

}

public void fuc()

{

System.out.println("into DChild#fuc");

}

}

public class DynamicBindingTest

{

public static void main(String[]args)

{

Base bs
=new Child();

bs.fuc();//dynamic binding derived Child so call Child#fuc

// bs.childMethod();//error:this method has been lost when upcasting to base class Base

Base cbs
=new CCChild();

cbs.fuc();

// bs.ccchildMethod();//error:this method has been lost when upcasting to base class Base

System.out.println("=================");

Child c=new Child();

CCChild ccc=new CCChild();

DChild dc=new DChild();

testCall(c);

testCall(ccc);

testCall(dc);

}

static void testCall(Base b)

{

b.fuc();

}

}

控制台打印出来的结果

into Child#fuc

into CCChild#fuc

================

into Child#fuc

into CCChild#fuc

into DChild#fuc