用接口编求长方形面积的Java程序

interface Figure{
public int area(int a,int b);
}

class Rectangle implements Figure{
public int area(int a,int b){
return a*b;
}

public static void main (String[] args) {
Rectangle r=new Rectangle();
System.out.println("面积是："+r.area(2,3));
}
}

------接口
public interface IS {
public int mianji(int l,int w);
}
-------实现类
public class changfang implements IS {

public int mianji(int l,int w) {
return l*w;
}

}
-------main函数
public class Test
{
public static void main(String args[])
{
int l=3;
int w=2;
IS is=new changfang();
int s=is.mianji(l, w);
System.out.println(s);
}

}