[java] How to calculate the running time of my program?

I wrote a program and now I want to calculate the total running time of my program from start to end.

How can I do this?

Use System.currentTimeMillis() or System.nanoTime() if you want even more precise reading. Usually, milliseconds is precise enough if you need to output the value to the user. Moreover, System.nanoTime() may return negative values, thus it may be possible that, if you're using that method, the return value is not correct.

A general and wide use would be to use milliseconds :

long start = System.currentTimeMillis();

... 


long end = System.currentTimeMillis();

NumberFormat formatter = new DecimalFormat("#0.00000");
System.out.print("Execution time is " + formatter.format((end - start) / 1000d) + " seconds");

Note that nanoseconds are usually used to calculate very short and precise program executions, such as unit testing and benchmarking. Thus, for overall program execution, milliseconds are preferable.

The general approach to this is to:

1. Get the time at the start of your benchmark, say at the start of main().
2. Run your code.
3. Get the time at the end of your benchmark, say at the end of main().
4. Subtract the start time from the end time and convert into appropriate units.

A hint: look at System.nanoTime() or System.currentTimeMillis().

You need to get the time when the application starts, and compare that to the time when the application ends.

Wen the app starts:

Calendar calendar = Calendar.getInstance();

// Get start time (this needs to be a global variable).
Date startDate = calendar.getTime();

When the application ends

Calendar calendar = Calendar.getInstance();

// Get start time (this needs to be a global variable).
Date endDate = calendar.getTime();

To get the difference (in millseconds), do this:

long sumDate = endDate.getTime() - startDate.getTime();

At the beginning of your main method, add this line of code :

final long startTime = System.nanoTime();

And then, at the last line of your main method, you can add :

final long duration = System.nanoTime() - startTime;

duration now contains the time in nanoseconds that your program ran. You can for example print this value like this:

System.out.println(duration);

If you want to show duration time in seconds, you must divide the value by 1'000'000'000. Or if you want a Date object: Date myTime = new Date(duration / 1000); You can then access the various methods of Date to print number of minutes, hours, etc.

Beside the well-known (and already mentioned) System.currentTimeMillis() and System.nanoTime() there is also a neat library called perf4j which might be useful too, depending on your purpose of course.