Timer.java

// $Id$
//
// Cassowary Incremental Constraint Solver
// Original Smalltalk Implementation by Alan Borning
// This Java Implementation by Greg J. Badros, <gjb@cs.washington.edu>
// http://www.cs.washington.edu/homes/gjb
// (C) 1998, 1999 Greg J. Badros and Alan Borning
// See ../LICENSE for legal details regarding this software
//
// Timer, adapted from John P. Russo's C++ Timer class

package EDU.Washington.grad.gjb.cassowary;

public class Timer
{
  public Timer() {
    TimerIsRunning = false;         // Start not yet called.
    ElapsedMs   = 0;             // No time on timer object yet.
  }
  

  public void Start() {
    //  Stopwatch is now running
    TimerIsRunning = true;
    //  Look at internal clock and remember reading
    StartReading   = System.currentTimeMillis();
  }

  public void Stop() {
    TimerIsRunning = false;                       //  Stop timer object.
    ElapsedMs += System.currentTimeMillis() - StartReading;
  }

  //  Clears a Timer of previous elapsed times, so that a new event
  //  can be timed.
  public void Reset() {
    TimerIsRunning = false;             // Start not yet called.
    ElapsedMs   = 0;             // No time on timer object yet.
  }

  // The data member, "TimerIsRunning" is used to keep track of
  // whether a timer is active, i.e. whether an event is being
  // timed. While we want those using the timer class to know when a
  // timer is active, we do NOT want them to directly access the
  // TimerIsRunning variable. We solve this problem, by making
  // TimerIsRunning private and providing the public "access function"
  // below.

  public boolean IsRunning() {
    return TimerIsRunning;
  }
  
  // This function allows a client to determine the amount of time that has
  // elapsed on a timer object. Note that there are two possibilities:

  // 1)  A timer object has been started and stopped. We can detect this
  //     case, because the variable "TimerIsRunning" is false.

  // 2)  A timer object is "running", i.e. is still in the process of timing
  //     an event. It is not expected that this case will occur as frequently
  //     as case 1).

  // In either case, this function converts ticks to seconds. Note that
  // since the function TicksPerSecond() returns a value of type double,
  // an implicit type conversion takes place before doing the division
  // required in either case.

  public double ElapsedTime() {
    if ( !TimerIsRunning )                            // Normal case
      return (double) ElapsedMs/1000;
    else
      return (double) (ElapsedMs + System.currentTimeMillis() - StartReading)/1000;
  }

  private boolean TimerIsRunning;
  private long ElapsedMs;
  private long StartReading;
}