Is there a stopwatch in Java?

java

performance

best-practices

tools

byNikita Barsukov·Feb 25, 2025

Use System.nanoTime() for precise timing in Java. Here's a simplified example of a stopwatch:

public class Stopwatch {
    private long start = System.nanoTime();

    public long elapsedMillis() {
        return (System.nanoTime() - start) / 1_000_000;
    }

    public static void main(String[] args) {
        Stopwatch sw = new Stopwatch();
        // Code to time goes here, like making coffee or saving the world. You decide.
        System.out.println("Execution Time: " + sw.elapsedMillis() + " ms"); // Wow, that was fast!
    }
}

You spark the stopwatch immediately with object creation and then gauge the elapsed time in milliseconds with elapsedMillis(). The mission to be timed must kick-off right after you create the Stopwatch object.

Precision and Performance — Between a Rock and a Hard Place

When timing in Java, be careful to find the right balance between value precision and avoiding any potential performance penalties. System.nanoTime() is optimized for precision, but beware of the costs, particularly in high-frequency scenarios where the frequent calling can affect performance.

Harnessing the Power of Libraries for Stopwatch

But wait, there's more! If you're after more functionality, try Apache Commons' StopWatch or Guava's Stopwatch. They bring more to the table, allowing you to have formatted outputs and they also allow you to settle for alternative time sources for testing. Now that's a sweet deal!

// Let's start with Guava Stopwatch
Stopwatch stopwatch = Stopwatch.createStarted();

// Code to save the world again goes here

long elapsedMillis = stopwatch.elapsed(TimeUnit.MILLISECONDS);
stopwatch.stop(); // Stop right there, stopwatch!
System.out.println("Execution Time: " + elapsedMillis + " ms"); // You did it again, hero!

Working with Spring? Then the Spring fam's StopWatch, from the spring-core module, got you covered. It will blend right into the ecosystem, like milk in your coffee.

The Java Epoch — `Instant` and `Duration`

Java's modern Date-Time API brought in Instant and Duration for precise handling of time. Think of them as superheroes who can handle time-travel like it's a piece of cake. It can even output the result in a universally recognized format, ISO 8601.

Instant start = Instant.now();

// Yes, you guessed right, world-saving code goes here again

Instant end = Instant.now();
Duration timeElapsed = Duration.between(start, end);
System.out.println("Execution Time: " + timeElapsed.toMillis() + " ms"); // That was close, almost ran out of time!

Who'd have thought that being thread-safe and immutable would be so crucial! It's like having a secret base or a fortress.

Pitfalls in Time Measurements — Avoid Getting Stuck in the Quantum Realm

If your stopwatch often reads zero, maybe your time-machine is broken. You might need to take a step back and check for accuracy problems in your time-calculation methods. Remember, nanoTime is relative — it's perfect for measuring intervals, but not ideal for current timestamps.

Choosing a Stopwatch — Like Choosing a Superpower

Each stopwatch method comes with its perks and quirks. For simplicity, System.nanoTime() is the way to go. But for complex needs, libraries like Guava or Spring pack a powerful punch and come with additional features. It's like choosing your superpower — pick wisely!

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