This blog will provide some code which allows you to determine multiple clicks in Java. The current version is using System.in as input (and thereby requires the user to press enter), but could easily be extend to work in a Swing setting (use KeyListener class).

The base code was developed as part of an internal “Java festival” at my company Bouvet. The assignment this time was to develop the behaviour for a tank, which would battle against other people’s tanks. We were allowed one key for input, which originally was intended to be used for strategy changing, but instead we used this one key to control the entire tank. By pressing once on the enter key, it would turn 90 degree clockwise, by pressing twice, it would turn 90 degrees anti-clockwise, by pressing three times, it would fire, and by pressing four times it would release a mine.

The provided solution consist of four class:

• IMultipleClickHandler: Interface to be implemented by the class which wants to receive a call when the click is performed (not each individual, only the last one)
• Engine: Class which sets up the MultipleClickThread and receives the event when it is performed
• MultipleClickThread: The core of the solution. Reads from System.in and creates a MultipleClickTimeoutThread with details of how many clicks have been performed so far. If a new click is received before the timeout, it aborts the current thread and creates a new one
• MultipleClickTimeoutThread: A simple thread which sleeps for certain time period, and if it has not been aborted in the meantime, it sends an event to the provided IMultipleClickHandler

Code:

package org.elsewhat.multipleclick;

public interface IMultipleClickHandler {
	/**
	 * Method called when the provided number of clicks have occured
	 * 
	 * @param nrOfClicks 
	 */
	public void clickOccured(int nrOfClicks);
}

package org.elsewhat.multipleclick;

public class Engine implements IMultipleClickHandler {

	public static void main(String[] args) {
		Engine eng= new Engine();
	}

	public Engine(){
		System.out.println("MultipleClick handler by Dagfinn Parnas. Please click enter multiple times for input");
		MultipleClickThread clickThread= new MultipleClickThread(this);
		clickThread.start();
	}

	public void run(){

		//do other Threadstuff

	}

	/**
	 * Method called when the provided number of clicks have occured
	 * in the MultipleClickThread
	 * 
	 * @param nrOfClicks 
	 */
	public void clickOccured(int nrOfClicks) {
		System.out.println("Engine received a "+ nrOfClicks + "-click");

	}
}

package org.elsewhat.multipleclick;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class MultipleClickThread extends Thread {
	private IMultipleClickHandler handler;
	public MultipleClickThread(IMultipleClickHandler handler){
		this.handler=handler;
	}

	/* How long should we allow between clicks */
	private long msMaxBetweenClicks = 300;

	public void run() {
		MultipleClickTimeoutThread clickTimeoutThread=null;
		// read from System.in
		BufferedReader input = new BufferedReader(new InputStreamReader(
				System.in));
		long msLastClick = 0;
		int nrClicks = 0;
		char character=0;
		// run forever till canceled by creator
		while (true) {

			//read from the input
			try {
				character =(char) input.read();
			}catch (IOException e) {
				e.printStackTrace();
			}
			// here we only process enter, i.e. CR (13) characters
			if (character == 13) {
				// if we have a click within the timeout period of the last
				// click
				if (System.currentTimeMillis() - msLastClick < msMaxBetweenClicks) {
					// abort old thread if it is not null
					if(clickTimeoutThread!=null){
						clickTimeoutThread.abort();
						clickTimeoutThread = null;
					}
				} else {
					nrClicks = 0;
				}
				nrClicks++;
				// System.out.println("Pressed once");
				clickTimeoutThread = new MultipleClickTimeoutThread(handler,msMaxBetweenClicks, nrClicks);
				clickTimeoutThread.start();
				msLastClick = System.currentTimeMillis();
			}
		}
	}

}

package org.elsewhat.multipleclick;

public class MultipleClickTimeoutThread extends Thread  {
	private long waitms;
	private boolean aborted=false;
	private IMultipleClickHandler handler;
	private int nrOfClicks;

	public MultipleClickTimeoutThread(IMultipleClickHandler handler, long waitms, int nrOfClicks){
		this.handler=handler;
		this.waitms=waitms;
		this.nrOfClicks=nrOfClicks;

	}

	public void abort(){
		aborted=true;
	}

	public void run() {
		try {
			sleep(waitms);
		} catch (Throwable t){

		}
		//if we're not aborted, then no extra clicks occured. Therefore, call handler
		if (!aborted){
			handler.clickOccured(nrOfClicks);
		}
	}
}