使用Class对象调用newInstance()实例化一个className类的对象时，className必须有无参数的构造方法
import java.lang.reflect.*;
class Rect
{
double width,height,area;
Rect(double w,double h)
{
width=w;
height=h;
}
public double getArea()
{
area=width*height;
return area;
}
}
public class hello {
public static void main(String[] args)
{
try
{
Class cs=Class.forName("Rect");
Rect rect=(Rect)cs.newInstance();
rect.width=100;
rect.height=10;
System.out.println(rect.getArea());
}
catch(Exception e)
{
System.out.println(e.toString());
}
}
}
