5-2：编写一个抽象类，给出三个子类，用上转型对象调用方法f()，g()，h()。

abstract class Operation5_2_1{
    public abstract void f(int x);
    public abstract void g(int x,int y);
    public abstract double h(double x);
}
class O1 extends Operation5_2_1{
    public void f(int x){
        System.out.println("O1.f"+x);
    }
    public void g(int x,int y){
        System.out.println("O1.g"+x+","+y);
    }
    public double h(double x){
        System.out.println("O1.h");
        return 0;
    }
}
class O2 extends Operation5_2_1{
    public void f(int x){
        System.out.println("O2.f"+x);
    }
    public void g(int x,int y){
        System.out.println("O2.g"+x+","+y);
    }
    public double h(double x){
        System.out.println("O2.h");
        return 0;
    }
}
class O3 extends Operation5_2_1{
    public void f(int x){
        System.out.println("O3.f"+x);
    }
    public void g(int x,int y){
        System.out.println("O3.g"+x+","+y);
    }
    public double h(double x){
        System.out.println("O3.h");
        return 0;
    }
}
public class Operation5_2_2{
    public static void main(String args[]){
        Operation5_2_1 Onew=new O1();
        Onew.f(1);
        Onew.g(1,1);
        Onew.h(1);
        Onew=new O2();
        Onew.f(2);
        Onew.g(2,2);
        Onew.h(2);
        Onew=new O3();
        Onew.f(3);
        Onew.g(3,3);
        Onew.h(3);    
    }
}