Thread: 'BufferedReader' problem...

hi every1...
i am new on this site...
i need help...
here is the program...

/*Program with class name 'Volume' using function overloading to compute the volume of cube, a sphere and a cuboid.Let the user input the values and his choice*/
import java.io.*;
class Volume
{
public void main() throws IOException
{
BufferedReader ob=new BufferedReader(new InputStreamReader(System.in));
System.out.println("A.Volume of cube\nB.Volume of sphere\nC.Volume of cuboid\nEnter choice according to the menu.");
char ch=(char)ob.read();
final double P=3.14;
Volume ob1=new Volume();
if(ch=='A')
{
System.out.println("Enter the side of the cube...");
double s=Double.parseDouble(ob.readLine());
ob1.volu(s);
}
if(ch=='B')
{
System.out.println("Enter the radius of the sphere...");
double r=Double.parseDouble(ob.readLine());
ob1.volu(r,P);
}
if(ch=='C')
{
System.out.println("Enter the length, breadth and height of the cuboid...");
double l=Double.parseDouble(ob.readLine());
double b=Double.parseDouble(ob.readLine());
double h=Double.parseDouble(ob.readLine());
ob1.volu(l,b,h);
}
}
public void volu(double side)
{
System.out.println("Volume of cube:");
double vol=side*side*side;
System.out.println(vol);
}
public void volu(double radius,double pi)
{
System.out.println("Volume of sphere:");
double vol=(4/3)*pi*radius*radius*radius;
System.out.println(vol);
}
public void volu(double length,double breadth,double height)
{
System.out.println("Volume of cuboid:");
double vol=length*breadth*height;
System.out.println(vol);
}
}


Output

A.Volume of cube
B.Volume of sphere
C.Volume of cuboid
Enter choice according to the menu.
A
Enter the side of the cube...

[after this the following error is observed]

java.lang.NumberFormatException: empty String
at sun.misc.FloatingDecimal.readJavaFormatString(Floa tingDecimal.java:994)
at java.lang.Double.parseDouble(Double.java:510)
at Volume.main(Volume.java:15)

so, this is the program...

i hv also found a solution to this...
the solution is that if a make a new object inside every if block, then the number can be inputted and the error is not observed(for example)

if(ch=='A')
{
BufferedReader ob2=new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter the side of the cube...");
double s=Double.parseDouble(ob2.readLine());
ob1.volu(s);
}

but, my question is that why cant we input a number using BufferedReader inside the if block, 'if' is not a function that we have to declare a variable again and again...

so this is it...
plz HELP...

Looks like BufferedReader does not have any method to read doubles, i have eclipse and that one shows me all methods of this class. I am not that experienced and i think that the keyboard is the input for your program, and if you want to read from keyboard using this constructor

Scanner tastatura = new Scanner(System.in);

, Scanner class has method to read double from keyboard. And Scanner can also read from files with this one

Scanner in = new Scanner(new File(url));

and there url is the path to the file.

NumberFormatException: empty String

With just a bit more programming you can prevent this.
Read the user's input into a String and test if the String is empty. If it is ask the user to enter again.
If you want to force the user to enter good data, you could write a method to prompt the user for the data, test for good data and ask again if it is bad. Otherwise convert it to a double and return the double.
Another thing to consider is to put the parseDouble call in try{}catch block to catch bad data.

And another consideration: Use the Scanner class. It has methods to test if the next data is a double before you read it.