Why Java’s Date isn’t deprecated, even though it might look like it

This shouldn’t be news at this point (JDK 1.5 was released 5 years ago), but in Java 5 Sun decided to deprecate large swaths of java.util.Date’s methods and constructors and introduce the Calendar class, which can handle locale-specific conversions and manipulations of the units of time we humans are used to seeing. This has created some confusion here and there about whether to represent datetimes as Dates or as Calendars, as it looks at a casual glance like Date has been more or less completely deprecated. It remains, however, as the preferred way of representing datetimes in Java. An explanation is after the jump.

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Running Standard Deviations

Update, 7/13/2013: I’m amazed at the continued staying power of this post, considering that I had originally worked the math out for this 14 years ago. People are still commenting on this and suggesting fixes. I’m also amazed that I’ve peppered enough errors in the math and code for people to still be finding errors 5 years after the fact.

My friend Dan at Invisible Blocks came up with a great way to compute a long-running mean from the count and mean:

count += 1
mean += (x - mean) / count

I remembered that I had come up with a similar thing for standard deviation back when I was developing clustering algorithms that could use that value. It uses a power sum average, where you track the power sum as an average (divide the power sum by n) in a similar way.

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