Reading in Program Output at command line...?!?

[Mike Smike]

Hi guys

Is there a way to Buffer in the output from a program which writes to the command line? At the moment, I am using

 BufferedReader keyboardInput = new BufferedReader(new InputStreamReader(System.in)); 

But that doesn't seem to read any of the output from my program.

My program asks for input at the command line. I have a GUI running simultaneously which uses System.out.print("...") to print coordinates from the clicked sqare to the command line. I want the program to read in the coordinates that appear at the command line as if they were text from the keyboard. I don't know if I've explained that very well?
Here's the method

  public void readIn() throws IOException
    {
        BufferedReader keyboardInput = new BufferedReader(new InputStreamReader(System.in));
        System.out.flush();
        System.out.println("Enter the coordinates:");
        System.out.flush();
        String coordString = keyboardInput.readLine();
        System.out.println("hello" + coordString);
    }

After clicking squares in the GUI, the coordinates appear in the right place, but they are not read by the BufferedReader?

Please help

Thanks muchos amigos.

Mike

[Paul Santa Maria]

Hi -

1. Your code seems to work fine: to accept keyboard input from
a console mode Java application, you must indeed read from System.in,
just as you're doing. I cut/pasted your code; here's the output:

/**
 * Trying to read from stdin
 *
 * EXAMPLE COMPILE/RUN:
 *
 * C:\temp>java hello2 =>
 *   calling readIn()...
 *   Enter the coordinates:
 *   1.3 2.5
 *   hello: 1.3 2.5
 *   done.
 */
import java.io.*;
 
class hello2 {
  public void readIn() throws IOException {
    BufferedReader keyboardInput = 
      new BufferedReader(
        new InputStreamReader(System.in) );
    System.out.flush();        
    System.out.println("Enter the coordinates:");        
    System.out.flush();        
    String coordString = keyboardInput.readLine();        
    System.out.println("hello: " + coordString); 
  }
 
  public static void main (String[] args) {
    System.out.println ("calling readIn()...");
    hello2 h = new hello2();
    try {
      h.readIn ();
    }
    catch (Exception e) {
      System.out.println ("readIn failed: " + e.getMessage ());
    }
    System.out.println ("done.");
  }
} 

2. Perhaps you're confusing reading command line arguments with reading
text from stdin. Here's how you can read command line arguments:

/**
 * hello: minimal cmd-line program
 *
 * EXAMPLE 1: Read parameters from the program's command line
 *
 * C:\temp>java hello a b c =>
 *   #/args= 3
 *   arg[0]= a
 *   arg[1]= b
 *   arg[2]= c
 */
class hello {
  public static void main (String[] args) {
    System.out.println ("#/args= " + args.length);
    for (int i = 0; i< args.length; i++) {
      System.out.println ("arg[" + i + "]= " + args[i]);
    }
  }
}

3. I'm not sure I've completely understood your question, howevever.

In general, what you're doing *should* work.

One final suggestion: you might want to consider accepting arguments from a Swing GUI. It's really quite easy: certainly not too much more difficult trying to read and parse from System.in!

'Hope that helps .. PSM
[ October 23, 2004: Message edited by: Paul Santa Maria ]

[Mike Smike]

Hi, thanks for the reply! It doesn't really solve my problem though. If you run the program, and then type in the coordinates (like you did - 1.3 2.5) then it does read them in. However, I am not typing in the co-ordinates. I have a GUI running independently. It is a grid of squares each with their own co-ordinate. When you click on the square, the listener uses System.out.print(...) to print the coordinates to the command line. So the co-ordinates are not typed in using the keyboard, they just appear when you click on a square.

Because of this, the System Reader doens't seem to read them in. The output looks like

 
Enter the coordinates:
[I] (so I click the squares (1,3) (2,9) and (7,6) for example) [/I]
(1,3) (2,9) (7,6)
[I](then I press enter)[/I]
hello
 

So only "hello" is printing out, which means the coordinates are not being read in.

Hope you can help

Thanks!

[Paul Santa Maria]

Hi, again -

1. I think your original question is answered:
a) Yes, "System.in" is the correct way to read with "standard input" from a Java program and

b) Yes, you seem to be doing it correctly.

2. Not certain what exactly you were trying to do, I took a couple guesses that I thought might help:
a) Q: Are you clear about the distinction between command-line arguments (which are read from "args[]") and standard input (which you read from "System.in")?
A: The answer appears to be "Yes" - you're definitely trying to read from standard input.


b) Q: would you be inclined to using a GUI instead of stdin/stdout?
A: The answer also appears to be "Yes"; you're definitely using a GUI, but I'm not clear if it's Swing ... or Something Else...

3. I've still got many questions (what platform are you on? Are we dealing with one program, or multiple concurrent programs? If so, are both written in Java? Does one invoke the other, or are they both started independently? Etc etc etc). But I really don't think it would be helpful for us to go there.

I've got three suggestions (which may or may not be of help):

a) You might want to modify my (working) test program to try to reproduce the problem. This, in turn, might give you the solution.

b) You might want to consider another way to communicate between your two programs (assuming there *are* two programs). For example: a disk file, a TCP/IP socket or perhaps even JMS.

c) Bear in mind that "communications" involves both:

- The *transport* (standard I/O, file I/O, socket I/O, etc)

- Some form of *synchronization* (is the listener actually ready to
receive before the sender transmits?

Again, I hope that helps!

And please: let us know how you ultimately resolve the problem!