How can I count the time it takes a function to complete in Java?

Here is how can compute the elapsed time.

// Get current time
long start = System.currentTimeMillis();

// Do something ...

// Get elapsed time in milliseconds
long elapsedTimeMillis = System.currentTimeMillis()-start;

// Get elapsed time in seconds
float elapsedTimeSec = elapsedTimeMillis/1000F;

// Get elapsed time in minutes
float elapsedTimeMin = elapsedTimeMillis/(60*1000F);

// Get elapsed time in hours
float elapsedTimeHour = elapsedTimeMillis/(60*60*1000F);

// Get elapsed time in days
float elapsedTimeDay = elapsedTimeMillis/(24*60*60*1000F);

long start = System.nanoTime();    
methodToBeTimed();
long elapsedTime = System.nanoTime() - start;