Measure execution time for a Java method [duplicat

Question

This question already has answers here:

How do I time a method's execution in Java? (38 answers)

Closed 6 years ago.

How do I calculate the time taken for the execution of a method in Java?

Answer 1

You can take timestamp snapshots before and after, then repeat the experiments several times to average to results. There are also profilers that can do this for you.

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From "Java Platform Performance: Strategies and Tactics" book:

With System.currentTimeMillis()

class TimeTest1 {
   public static void main(String[] args) {

      long startTime = System.currentTimeMillis();

      long total = 0;
      for (int i = 0; i < 10000000; i++) {
         total += i;
      }

      long stopTime = System.currentTimeMillis();
      long elapsedTime = stopTime - startTime;
      System.out.println(elapsedTime);
   }
}

With a StopWatch class

You can use this StopWatch class, and call start() and stop before and after the method.

class TimeTest2 {
   public static void main(String[] args) {

      Stopwatch timer = new Stopwatch().start();

      long total = 0;
      for (int i = 0; i < 10000000; i++) {
         total += i;
      }

      timer.stop();
      System.out.println(timer.getElapsedTime());
   }
}

See here.

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NetBeans Profiler:

Application Performance Application

Performance profiles method-level CPU performance (execution time). You can choose to profile the entire application or a part of the application.

See here.

Answer 2

As proposed nanoTime () is very precise on short time scales. When this precision is required you need to take care about what you really measure. Especially not to measure the nanotime call itself

long start1 = System.nanoTime();
// maybe add here a call to a return to remove call up time, too.
// Avoid optimization 
long start2 = System.nanoTime();
myCall(); 
long stop = System.nanoTime();
long diff = stop - 2*start2 + start1;

System.out.println(diff + " ns");

By the way, you will measure different values for the same call due to

• other load on your computer (background, network, mouse movement, interrupts, task switching, threads)
• cache fillings (cold, warm)
• jit compiling (no optimization, performance hit due to running the compiler, performance boost due to compiler (but sometimes code with jit is slower than without!))