currentTimeMillis
First, you can use the currentTimeMillis method. It returns time in milliseconds (1/1000 second)
counted from midnight UTC on January 1, 1970. If you convert currentTimeMillis output to Date,
you can get the current date.
long start = System.currentTimeMillis();
// ... logic omitted
long end = System.currentTimeMillis();
System.out.println("Elapsed time: " + (end - start) + " ms");
In practice, currentTimeMillis may not be ideal for measuring code performance.
Because it is wall-clock time, external workload or system time changes can affect measurements.
So it is better suited for date-related calculations, while nanoTime below provides more accurate execution-time measurement.
nanoTime
nanoTime measures elapsed time from an arbitrary origin in nanoseconds.
The code structure is similar to currentTimeMillis,
but it is not tied to system clock changes or wall-clock time.
long start = System.nanoTime();
// ... logic omitted
long end = System.nanoTime();
System.out.println("Elapsed time: " + (end - start) + " ns");
One thing to note: it measures relative to the JVM (Java Virtual Machine). As a result, measurements can differ across different JVMs. In other words, measuring on the same server is generally fine, but results can vary across different servers.
Instant
The Instant class represents a point on the timeline. Its timestamp uses midnight UTC on January 1, 1970 as zero,
and represents elapsed time after that as positive or negative values.
With between in Instant, you can get the duration between two Instant objects.
The return type is Duration, which you can convert to milliseconds via toMillis.
Instant start = Instant.now();
// ... logic omitted
Instant end = Instant.now();
System.out.println("Elapsed time: " + Duration.between(start, end).toMillis() + " ms");
StopWatch
Next is a library-based approach. Apache commons-lang3 includes a StopWatch class.
StopWatch stopWatch = new StopWatch();
stopWatch.start();
// ... logic omitted
stopWatch.stop();
System.out.println("Elapsed time: " + stopWatch.getTime() + " ms");
Spring Framework also provides a StopWatch class.
Note that both Apache and Spring StopWatch classes are not thread-safe.
StopWatch stopWatch = new StopWatch();
stopWatch.start();
// ... logic omitted
stopWatch.stop();
System.out.println(stopWatch.prettyPrint());
Spring’s StopWatch class has a prettyPrint method, which prints formatted output as the name suggests.
StopWatch '': running time = 3768817 ns
---------------------------------------------
ns % Task name
---------------------------------------------
003768817 100%
Because usage is simple and it provides utility methods for execution-time measurement,
StopWatch is often the most practical choice.