Stopwatch

java.lang.Object
- com.google.common.base.Stopwatch

```
@GwtCompatible
public final class Stopwatch
extends java.lang.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.
Warning for Android users: a stopwatch with default behavior may not continue to keep time while the device is asleep. Instead, create one like this:
```
   

    Stopwatch.createStarted(
         new Ticker() {
           public long read() {
             return android.os.SystemClock.elapsedRealtime();
           }
         });
```
Since:

10.0

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`static Stopwatch`	`createStarted()`	Creates (and starts) a new stopwatch using `System.nanoTime()` as its time source.
`static Stopwatch`	`createStarted(Ticker ticker)`	Creates (and starts) a new stopwatch, using the specified time source.
`static Stopwatch`	`createUnstarted()`	Creates (but does not start) a new stopwatch using `System.nanoTime()` as its time source.
`static Stopwatch`	`createUnstarted(Ticker ticker)`	Creates (but does not start) a new stopwatch, using the specified time source.
`long`	`elapsed(java.util.concurrent.TimeUnit desiredUnit)`	Returns the current elapsed time shown on this stopwatch, expressed in the desired time unit, with any fraction rounded down.
`boolean`	`isRunning()`	Returns `true` if `start()` has been called on this stopwatch, and `stop()` has not been called since the last call to `start()`.
`Stopwatch`	`reset()`	Sets the elapsed time for this stopwatch to zero, and places it in a stopped state.
`Stopwatch`	`start()`	Starts the stopwatch.
`Stopwatch`	`stop()`	Stops the stopwatch.
`java.lang.String`	`toString()`	Returns a string representation of the current elapsed time.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- 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:
    
    java.lang.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:
    
    java.lang.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(java.util.concurrent.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
```
public java.lang.String toString()
```
    Returns a string representation of the current elapsed time.
    
    Overrides:
    
    toString in class java.lang.Object

Class Stopwatch

Method Summary

Methods inherited from class java.lang.Object

Method Detail

createUnstarted

createUnstarted

createStarted

createStarted

isRunning

start

stop

reset

elapsed

toString