Reading files

So here we go, hope this is an alright place to post this.

It's very much a personal project, just something I've set myself to try and further my knowledge of java. I only started studying it this year so I'm pretty useless so far.

Basically, the end aim is to develop a piece of code that will go through a file, copy all the lines that begin with a number and then insert them into a new file.

I've started off with a piece of code that will read through a file and display the letter "Y" when the line begins with an 'A' and display the letter "N" when it begins with anything else. The only way I know how to go through an entire file is to use:

while(MyFile.readLine()!=null)

However, I want it to be able to process lines that have nothing on them.

The code I've got so far is:

Quote:

---

import java.io.*;

class test1
{
public static void main(String[] args) throws IOException
{
FileReader file = new FileReader("body.txt");
BufferedReader MyFile = new BufferedReader(file);

String text = MyFile.readLine();

while(text!=null)
{
if(text.charAt(0)=='A')
{
System.out.println("Y");
}

else
{
System.out.println("N");
}
text = MyFile.readLine();
}

MyFile.close();
}
}

---

body.txt is simply

Quote:

---

A
B
B
A
B
B
A
A
A

---

However, if there is an empty line in the middle of body.txt, it obviously won't work. Any help would be greatly appreciated!

Many thanks.

I actually think what you have should work. No reason why a blank line should stop the loop. It will read the entire file. So for instance, if you have a file with 7 lines:
A
B
C

D
E
F

It will evaluate all the way to the F. Heres a sample of the File reader, but it's very similar to what you have. What output are you seeing?

Code:

---

      try{
  // Open the file that is the first
  // command line parameter
  FileInputStream fstream = new FileInputStream("testing.txt");
  // Get the object of DataInputStream
  DataInputStream in = new DataInputStream(fstream);
  BufferedReader br = new BufferedReader(new InputStreamReader(in));
  String strLine;
  //Read File Line By Line
  while ((strLine = br.readLine()) != null)  {
  System.out.println(strLine);
  }
  //Close the input stream
  in.close();
    }catch (Exception e){//Catch exception if any
  System.err.println("Error: " + e.getMessage());
  }

---

That should produce the following output:

Code:

---

A
B
C

D
E
F

---

Quote:

---

it obviously won't work

---

Please explain the reason it won't work.

Quote:

---

I want it to be able to process lines that have nothing on them.

---

You can test the contents of the String that you read into to see if it is empty. See the String API for methods to use.

It won't work because a blank line does not have a char at index 0. Op will need to add a separate test for a blank line, such as testing the length of the String read in.

Yes, I saw that. I was wondering if that was the reason for the message the OP posted. You never know what a student thinks his code does or does not do. So I ask to be sure we are on the same page.
You'll note I recommended that the String be tested to see if it is empty which I thought would be a solution for the OPs problem.

Oops. I really have to read entire posts. ;)

The blank line will result in a zero length String so charAt( 0 ) will bomb.

I would test to see if the length of the text string is greater than 0 before seeing what the first character is.

Refer to the String class.

Another pointless post. Why do you bother when the problem has already been identified and a solution provided