Thread: How do i limit the input time

From where? The console? A GUI textbox?

hmmm, that's tricky...

I came up with a rudimentary solution which reads in from System.in in a separate thread and puts it into a StringBuilder buffer which can then be read externally. While someone else isn't actively trying to read from the reader, the buffer is emptied. Note that there needs to be synchronization between the two threads on the buffer otherwise bad things will happen.

This may be good enough to work with most user inputs, but you may want to improve on it. There are still a few issues (both those I have thought of and those I didn't think about).

import java.util.Scanner;
 
public class TimedScanner implements Runnable
{
	public static void main(String[] args)
	{
		TimedScanner scanner = new TimedScanner();
		System.out.print("Enter your name in 10 second: ");
		String name = scanner.nextLine(10000);
		if (name == null)
		{
			System.out.println("you were too slow.");
		}
		else
		{
			System.out.println("Hello, " + name);
		}
	}
 
	private Scanner scanner;
	private StringBuilder buffer;
	private boolean reading;
	private Thread t;
 
	public TimedScanner()
	{
		scanner = new Scanner(System.in);
		buffer = new StringBuilder();
		reading = false;
		t = new Thread(this);
		t.setDaemon(true);
		t.start();
	}
 
	public String nextLine(long time)
	{
		reading = true;
		String result = null;
		long startTime = System.currentTimeMillis();
		while (System.currentTimeMillis() - startTime < time && result == null)
		{
			try
			{
				Thread.sleep(30);
			}
			catch (InterruptedException e)
			{
			}
			synchronized (buffer)
			{
				if (buffer.length() > 0)
				{
					Scanner temp = new Scanner(buffer.toString());
					result = temp.nextLine();
				}
			}
		}
		reading = false;
		return result;
	}
 
	@Override
	public void run()
	{
		while (scanner.hasNextLine())
		{
			String line = scanner.nextLine();
			synchronized (buffer)
			{
				if (reading)
				{
 
					buffer.append(line);
					buffer.append("\n");
 
				}
				else
				{
					// flush the buffer
					if (buffer.length() != 0)
					{
						buffer.delete(0, buffer.length());
					}
				}
			}
		}
	}
}

isn't reading from InputStream e.g. System.in is a blocking call ?

Yes it is, which is what makes this task tricky. The code I had puts the blocking call in a separate thread and passes the data to a buffer, but it's hardly ideal.