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Asked: 2026-06-17T14:00:53+00:00

I’m realizing a cache with java, but I have the last problem to solve:

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I’m realizing a cache with java, but I have the last problem to solve: how to deal with elements’ deletion?

Elements are stored on the disk, each element has a validity period (then an expiration date) and also a size, my cache has obviously a maximum size and a maximum number of elements which may be stored.

I imagined three ways for performing elements’ deletion:

  1. When inserting a new element into the cache a scheduled thread (one for each element) is configured for starting at expiration time (in order to delete the element itself)
  2. Execute a thread each X minutes in order to check which elements may be deleted (and delete them)
  3. When a limit (size or number) is reached the oldest elements are deleted (or delete elements randomly (faster))

About the third point, using this policy the cache will continue to store also expired elements. Obviously when one of these is required a control is performed to check if the element is still valid.

What do you think about? What’s the common behavior when managing a cache? Are there other solutions?

P.S. I’m developing this cache for Android, but I think this is not so important.

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  1. Editorial Team

    Basically you have to know how often your cached elements will be used, and in which order. A cache has to do the same as an OS in order to keep the best data in memory.

    Hava a look at these strategies and take the one you need: http://en.wikipedia.org/wiki/Page_replacement_algorithm

    A good tip would be LRU (Least-Recently-Used). But like all these strategies it has some faults. Which may not be suitable for your case of usage.

    Implementation tips for LRU:

    use a PriorityQueue to store the elements in addition to your map. Keep it being updated with a global counter that gets incremented every time you use one of your elements and reinsert the corresponding element in the PriorityQueue with the current value of the global counter.

    If you need to remove an item from the queue, you just have to remove the first or last element from the queue (depending on your implementation of the compareTo(…) method). And remove it from the map as well.

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