jbuilder2005

				
				//lx3_7.java
				
				import java.io.*;
				public class  lx3_7{
				    public static void main(String args[ ])
				    {
				        double PI=3.141592654D;	//定义常量  
				        double r=0, area;
				        String S="";
				        System.out.println ( "圆的半径为：");
				        try{
				           BufferedReader in=new BufferedReader(new InputStreamReader(System.in));
				            S=in.readLine();
				            r= Double.parseDouble (S);
				            
				        } catch(Exception e){} 
				        area = PI * r * r;
				        System.out.println ("面积为："+area);
				    }
				}