com.google.common.base

Class Stopwatch


  • @Beta
 @GwtCompatible(emulated=true)
public final class Stopwatch
extends Object
    An object that measures elapsed time in nanoseconds. It is useful to measure elapsed time using this class instead of direct calls to System.nanoTime() for a few reasons:
    • An alternate time source can be substituted, for testing or performance reasons.
    • As documented by nanoTime, the value returned has no absolute meaning, and can only be interpreted as relative to another timestamp returned by nanoTime at a different time. Stopwatch is a more effective abstraction because it exposes only these relative values, not the absolute ones.

    Basic usage: 

       Stopwatch stopwatch = Stopwatch.createStarted();
   doSomething();
   stopwatch.stop(); // optional

   long millis = stopwatch.elapsed(MILLISECONDS);

   log.info("time: " + stopwatch); // formatted string like "12.3 ms"

    Stopwatch methods are not idempotent; it is an error to start or stop a stopwatch that is already in the desired state.

    When testing code that uses this class, use createUnstarted(Ticker) or createStarted(Ticker) to supply a fake or mock ticker. This allows you to simulate any valid behavior of the stopwatch.

    Note: This class is not thread-safe.

    Since:
    10.0

    • Method Detail

      • createUnstarted

        public static Stopwatch createUnstarted()
        Creates (but does not start) a new stopwatch using System.nanoTime() as its time source.
        Since:
        15.0

      • createUnstarted

        public static Stopwatch createUnstarted(Ticker ticker)
        Creates (but does not start) a new stopwatch, using the specified time source.
        Since:
        15.0

      • createStarted

        public static Stopwatch createStarted()
        Creates (and starts) a new stopwatch using System.nanoTime() as its time source.
        Since:
        15.0

      • createStarted

        public static Stopwatch createStarted(Ticker ticker)
        Creates (and starts) a new stopwatch, using the specified time source.
        Since:
        15.0

      • isRunning

        public boolean isRunning()
        Returns true if start() has been called on this stopwatch, and stop() has not been called since the last call to start().

      • start

        public Stopwatch start()
        Starts the stopwatch.
        Returns:
        this Stopwatch instance
        Throws:
        IllegalStateException - if the stopwatch is already running.

      • stop

        public Stopwatch stop()
        Stops the stopwatch. Future reads will return the fixed duration that had elapsed up to this point.
        Returns:
        this Stopwatch instance
        Throws:
        IllegalStateException - if the stopwatch is already stopped.

      • reset

        public Stopwatch reset()
        Sets the elapsed time for this stopwatch to zero, and places it in a stopped state.
        Returns:
        this Stopwatch instance

      • elapsed

        public long elapsed(TimeUnit desiredUnit)
        Returns the current elapsed time shown on this stopwatch, expressed in the desired time unit, with any fraction rounded down.

        Note that the overhead of measurement can be more than a microsecond, so it is generally not useful to specify TimeUnit.NANOSECONDS precision here.

        Since:
        14.0 (since 10.0 as elapsedTime())

      • toString

        @GwtIncompatible(value="String.format()")
public String toString()
        Returns a string representation of the current elapsed time.