How do I time a method's execution in Java?

Question

How do I get a method's execution time? Is there a Timer utility class for things like timing how long a task takes, etc?

Most of the searches on Google return results for timers that schedule threads and tasks, which is not what I want.

Answer 1

Use a profiler (JProfiler, Netbeans Profiler, Visual VM, Eclipse Profiler, etc). You'll get the most accurate results and is the least intrusive. They use the built-in JVM mechanism for profiling which can also give you extra information like stack traces, execution paths, and more comprehensive results if necessary.

When using a fully integrated profiler, it's faily trivial to profile a method. Right click, Profiler -> Add to Root Methods. Then run the profiler just like you were doing a test run or debugger.

Answer 2

This probably isn't what you wanted me to say, but this is a good use of AOP. Whip an proxy interceptor around your method, and do the timing in there.

The what, why and how of AOP is rather beyond the scope of this answer, sadly, but that's how I'd likely do it.

Edit: Here's a link to Spring AOP to get you started, if you're keen. This is the most accessible implementation of AOP that Iive come across for java.

Also, given everyone else's very simple suggestions, I should add that AOP is for when you don't want stuff like timing to invade your code. But in many cases, that sort of simple and easy approach is fine.

Answer 3

new Timer(""){{
    // code to time 
}}.timeMe();



public class Timer {

    private final String timerName;
    private long started;

    public Timer(String timerName) {
        this.timerName = timerName;
        this.started = System.currentTimeMillis();
    }

    public void timeMe() {
        System.out.println(
        String.format("Execution of '%s' takes %dms.", 
                timerName, 
                started-System.currentTimeMillis()));
    }

}

Answer 4

There is always the old-fashioned way:

long startTime = System.nanoTime();
methodToTime();
long endTime = System.nanoTime();

long duration = (endTime - startTime);  //divide by 1000000 to get milliseconds.

Answer 5

Using Instant and Duration from Java 8's new API,

Instant start = Instant.now();
Thread.sleep(5000);
Instant end = Instant.now();
System.out.println(Duration.between(start, end));

outputs,

PT5S

Answer 6

As "skaffman" said, use AOP OR you can use run time bytecode weaving, just like unit test method coverage tools use to transparently add timing info to methods invoked.

You can look at code used by open source tools tools like Emma (http://downloads.sourceforge.net/emma/emma-2.0.5312-src.zip?modtime=1118607545&big_mirror=0). The other opensource coverage tool is http://prdownloads.sourceforge.net/cobertura/cobertura-1.9-src.zip?download.

If you eventually manage to do what you set out for, pls. share it back with the community here with your ant task/jars.