java中继承的理解

class A{
double f(double x,double y){
return x+y;
}
}

class B extends A{
double f(int x,int y){
return x*y;
}
}
public class extend_1 {

public static void main(String[] args) {
// TODO Auto-generated method stub
B b=new B();
System.out.println(b.f(3, 5));
System.out.println(b.f(3.0, 5.0));
}

}

class C{
double f(double x,double y){
return x+y;
}
static int g(int n){
return n*n;
}
}

class D extends C{
double f(double x,double y){
double m=super.f(x,y);
return m+x*y;
}
static int g(int n){
int m=C.g(n);
return m+n;
}
}
public class extends_2 {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
D b=new D();
System.out.println(b.f(10.0, 8.0));
System.out.println(b.g(3));

}

}