/**
* @author mljinbo
* 在面向对象的继承方面，我们应尽量地继承于抽象类，而不是具体类,(如果是基于具体类的继承，很容易使对象在定义equals方法时出问题-----如传递性上；
* 抽象类的存在，就是用来继承的从来达到复用的目的，具体类的存在，是为了实现的）但有时是不得已要继承一个具体类，此时基类（父类）、派生类（子类）它们的方法和变量，
* 在调用时如何呢？
*/
class Father{
String name="father";
public void who(){
System.out.println("I am "+ name ) ;
say();
}
public void bye(){
System.out.println(name+ ": GoodBye" ) ;
}
public void say(){
System.out.println("Father :hello" ) ;
}
}
class Son extends Father{
String name="son";
public void who(){
System.out.println("Son :I am "+ name ) ;
say( ) ;
}
public void say(){
System.out.println("Son :hello" ) ;
}
}
public class Demo {
public static void main(String[] args){
/*当父类句柄变量变量f指向父类时，此时父类方法调用的全是自已的内容，如
* f.who()调用的name 是Father.name；who调用的方法也是Father
* 的方法是Father.say();此时该句柄变量所指的变量亦是Father.name即字符串"father"
*
*/
Father f=new Father();
f.who();
System.out.println(f.name);
f.bye();
System.out.println("\n\n" ) ;
/* 输出结果为：
* I am father
* Father :hello
* father
* father: GoodBye
*/
/*当子类句柄变量变量向子类时，此时子类方法调用的全是自已的内容，如
* s.who()调用的name 是Son.name；s.who调用的方法也是Son
* 的方法Son.say();s.name所指的变量亦是Son自己的变量Son.name即字符串"son"
* 字类句柄变量所指的子类对象的没有对应的方法，则子类会调用从父类继承的方法。父类的方法会自动调用父类的变量Father.name
* 而不是子类的变量Son.name;
*
*/
Son s=new Son( ) ;
s.who();
System.out.println(s.name);
s.bye();
System.out.println("\n\n" ) ;
/*输出结果为：
* Son :I am son
* Son :hello
* son
* father: GoodBye
*/
/*当父类句柄变量指向子类时，
* 此时句柄变量所指的方法调用的全是它实际所指对象的自已的内容，如
* s.who()调用的name 是Son.name；s.who调用的方法也是Son
* 的方法Son.say();但若用f.name ,则它指的是父类的内容Father.name
*/
Father fs= s;
// f.who();
fs.who();
System.out.println(fs.name);
fs.bye();
/* 输出结果:
* Son :I am son
* Son :hello
* father
* father: GoodBye
*/
}
}
关于为什么会这样，大家可从下面这段话里面找到启示
Since there are now two classes involved—the base class and the derived class—instead of just one, it can be a bit confusing to try to imagine the resulting object produced by a derived class. From the outside, it looks like the new class has the same interface as the base class and maybe some additional methods and fields. But inheritance doesn’t just copy the interface of the base class. When you create an object of the derived class, it contains within it a subobject of the base class. This subobject is the same as if you had created an object of the base class by itself. It’s just that from the outside, the subobject of the base class is wrapped within the derived-class object.---------------<<think in java>> 第三版Resuing classes
有不当的地方，还望更正......
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Last edited by mljinbo on 2005-6-30 at 19:36 ]
