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Comment by cirrus3 | Hacker News Reader

Why are you using the Calendar API in Java? It is full of issues like this.

I never really understood why not simply use milliseconds since the epoch and keep track of a time zone separately if needed... This allows fairly easy conversion to most native systems i have worked with, easy sorting and diff operations as well as final display control. Also don't have a need to be thinking about daylight savings then, or do other conversions for say timesheets.

It depends on what you need to do. If you just need to say when something happened (e.g. some log event) then milliseconds since the epoch is fine. If want a user to schedule a reoccurring meeting at 8am on the first Thursday of every month, you can also keep a set of timestamps as milliseconds since the epoch, but you are going to need to do some work to figure out the right numbers correctly.

> If want a user to schedule a reoccurring meeting at 8am on the first Thursday of every month, you can also keep a set of timestamps as milliseconds since the epoch

No, you can't really, especially if the recurring meetings go on more than a few years into the future. If the time zone rules themselves change (e.g. if the user's country abolishes or introduces DST), then the timestamps you stored will become wrong in light of the change.

Because a calendar date and a point in time are entirely different things.

Timezone rules change. If you want to be fully robust, you need to store the intent of the time

I didn't write the code originally; this was like 15 years ago. If the API still exists people will misuse it.

I don’t know anything about calendar pitfalls or Java, but I would have loved to see a better alternative suggested here.

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