SimpleTimer.java

/**
 * A simple timer class that allows you to keep track of how much time
 * has passed between events.
 * 
 * You use this class by creating a timer as a member field in your actor (or whatever):
 * <pre>
 * 
 * private SimpleTimer timer = new SimpleTimer();
 * </pre>
 * 
 * Then when you want to start the timer (for example, when a shot is fired), you call the mark() method:
 * 
 * <pre>
 * 
 * timer.mark();
 * </pre>
 * 
 * Thereafter, you can use the millisElapsed() method to find out how long it's been since mark()
 * was called (in milliseconds, i.e. thousandths of a second).  So if you want to only allow the player to fire a shot every second, you
 * could write:
 * 
 * <pre>
 * 
 * if (timer.millisElapsed() > 1000 && Greenfoot.isKeyDown("space"))
 * {
 *     // Code here for firing a new shot
 *     timer.mark(); // Reset the timer
 * }
 * </pre>
 * 
 * @author Neil Brown
 * @version 1.0
 */
public class SimpleTimer
{
    private long lastMark = System.currentTimeMillis();
    
    /**
     * Marks the current time.  You can then in future call
     * millisElapsed() to find out the elapsed milliseconds
     * since this mark() call was made.
     * 
     * A second mark() call will reset the mark, and millisElapsed()
     * will start increasing from zero again.
     */
    public void mark()
    {
        lastMark = System.currentTimeMillis();
    }
    
    /**
     * Returns the amount of milliseconds that have elapsed since mark()
     * was last called.  This timer runs irrespective of Greenfoot's
     * act() cycle, so if you call it many times during the same Greenfoot frame,
     * you may well get different answers.
     */
    public int millisElapsed()
    {
        return (int) (System.currentTimeMillis() - lastMark);
    }
}