Console clue ..

[berner2]

hi !
<newbie mode on priority=-10 >

I'm learning j2se and i'm trying to write a
simple console programm and I'm stuck with this :

i want the user to have 5 seconds to answer the question,
after 5 seconds system says ::bzzzzzzzzz time up :::::::
and next question starts ....
but i have a problem that I can't do anything
when system is waiting for user input

BufferedReader br ... ;
br.readLine();

if any one could give me a clue how to do this ..

I came up with an idea to do this in 2 threads
timer, and question .. something like that ...
is it the way ? ... but still it would hang on
readLine() i think ....

<newbie mode off>

Thanks !

 

[Andrew T.]

berner2 wrote:
....

I'm learning j2se and i'm trying to write a
simple console programm ....

Are you referring to the command line? Note that Java
is not a language well suited to interacting with the
command line, though a few more methods were added
in 1.5 (mostly for parsing input and output).

Andrew T.

 

[berner2]

berner2 wrote:
...

Are you referring to the command line? Note that Java
is not a language well suited to interacting with the
command line, though a few more methods were added
in 1.5 (mostly for parsing input and output).

Andrew T.

yes - the command line.
I think I'm gonna give up this one...
thanks anyway

 

[Christopher Benson-Manica]

i want the user to have 5 seconds to answer the question,
after 5 seconds system says ::bzzzzzzzzz time up :::::::
and next question starts ....
but i have a problem that I can't do anything
when system is waiting for user input

BufferedReader br ... ;
br.readLine();

This should be pretty simple:

Thread.sleep(5000);
if( System.in.available() > 0 ) {
// User entered some data, read and handle it
} else {
// Not
}

Note, of course, that the user will be waiting for 5 seconds whether
or not anything is entered, but that may be good enough for your
purposes.

(Disclaimer: I don't pretend to understand all the complexities that
you're likely to encounter by doing this, but it hopefully will be
something for you to explore.)

 

[Chris Uppal]

Thread.sleep(5000);
if( System.in.available() > 0 ) {
// User entered some data, read and handle it
} else {
// Not
}

Never use available().

That won't work (besides the problem you have already pointed out).

Available() will only answer how many bytes can be read without blocking (or,
more accurately, an unreliable and pessimistic estimate of how many bytes --
InputStream itself, for instance, is documented always to return 0). All it
can do is check its own buffers to see how much data is in them. That's
checking /its own/ buffers, not the OS's. In Unix whatever the user has typed
will still be in the TTY driver's buffers in the kernel, Java won't know
anything about it until it issues a read() -- at which time it will block
unless the user has already entered <carriage return> or <eof>. Roughly the
same is true on Windows.

Never use available().

-- chris

P.S. I don't think there is any way to do this which doesn't involve either
executing an external program or using JNI.

 

[Simon]

I came up with an idea to do this in 2 threads
timer, and question .. something like that ...
is it the way ? ... but still it would hang on
readLine() i think ....

I don't see a way to do it without threads. What about the following one?

Cheers,
Simon


import java.io.*;

public class ReadConsole {

private String input;

private void inputArrived(String input) {
// overwriting old value
// could also append it instead
this.input = input;
this.notify();
}

public void waitForInput() {

System.out.println("Question: What is 6x7?");

Thread inputThread = new Thread() {
public void run() {
try {
BufferedReader console = new BufferedReader(new InputStreamReader(System.in));
String line = console.readLine();
synchronized (ReadConsole.this) {
inputArrived(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
};
inputThread.setDaemon(true);
inputThread.start();

try {
synchronized (this) {
wait(5000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}

if (input == null) {
System.out.println("::bzzzzzzzzz time up :::::::");
} else {
System.out.println("Your answer: '" + input + "'");
}
}

public static void main(String[] argv) throws Exception {
new ReadConsole().waitForInput();

}

}

 

[Rogan Dawes]

Never use available().

That won't work (besides the problem you have already pointed out).

Available() will only answer how many bytes can be read without blocking (or,
more accurately, an unreliable and pessimistic estimate of how many bytes --
InputStream itself, for instance, is documented always to return 0). All it
can do is check its own buffers to see how much data is in them. That's
checking /its own/ buffers, not the OS's. In Unix whatever the user has typed
will still be in the TTY driver's buffers in the kernel, Java won't know
anything about it until it issues a read() -- at which time it will block
unless the user has already entered <carriage return> or <eof>. Roughly the
same is true on Windows.

Never use available().

-- chris

P.S. I don't think there is any way to do this which doesn't involve either
executing an external program or using JNI.

As you mentioned in another thread, there IS a solution to this, using a
thread dedicated to reading from System.in:

import java.io.InputStream;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.util.List;
import java.util.LinkedList;

public class ConsoleReader extends Thread {

private List<String> lines = new LinkedList<String>();
private BufferedReader reader;

public ConsoleReader(InputStream is) {
setDaemon(true);
reader = new BufferedReader(new InputStreamReader(is));
}

public void run() {
String line;
try {
while ((line = reader.readLine()) != null) {
synchronized(lines) {
lines.add(line);
lines.notifyAll();
}
}
} catch (IOException ioe) {
}
}

public String readLine(long timeout) {
synchronized(lines) {
lines.clear();
try {
lines.wait(timeout);
if (lines.size()>0)
return lines.get(0);
return null;
} catch (InterruptedException ie) {
return null;
}
}
}

public static void main(String[] args) {
ConsoleReader reader = new ConsoleReader(System.in);
reader.start();
System.out.println("Enter a line: ");
String line = reader.readLine(5000);
if (line == null) {
System.out.println("Timeout!");
} else {
System.out.println("You entered : '" + line + "'");
}
}

}