用java求圆的面积(自己输入数字)

import java.io.*;
public class bj {
public static void main(String[] args) throws IOException {
BufferedReader buf = new BufferedReader(
new InputStreamReader(System.in));
System.out.print("请输入半径: ");
String banjing = buf.readLine();
int bj=new Integer(banjing);
double s;
final float PI=3.14f;
s=PI*bj*bj;
System.out.println("半径为:" + s);
}
}

import java.io.*;
class test
{
public static void main(String []args)
{
int a;
a=MyInput.readInt();
System.out.println(a*a*3.14);
}
}

class MyInput
{
public static String readString()
{
BufferedReader br
=new BufferedReader(new InputStreamReader(System.in),1);
String string=" ";
try
{
string=br.readLine();
}
catch (IOException ex)
{
System.out.println(ex);
}