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Major Bug!! Java or android itself?

Discussion in 'Android Apps & Games' started by karimamin, Sep 3, 2010.

  1. karimamin

    karimamin Lurker
    Thread Starter

    If you run the following expression
    102 * 0.0254
    you will get 2.59079999999998

    but the answer is 2.5908
    But yet, multiple 102 * 0.0253 or 102*0.0255 or 102*0.0256 and you get the right answer!! Just with this number. This fails on both the emulator for eclipse and on my actual htc phone.:mad:

    Help! Can anyone help me solve this problem?
     



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  2. meackerman

    meackerman Newbie

    Welcome to the world of Java and double precision numbers. Same thing happens in Windows and everywhere else. Its not a "bug" but the way Java double precision numbers are implemented.
     
  3. karimamin

    karimamin Lurker
    Thread Starter

    I'm basically trying to make a simple calculator and found this number totally at random. The calculator on my phone calculates this properly so why can't my app? I guess i'm trying to get is what are the workarounds for this as I take it there must be for the calculator software to work properly.
     
  4. dCoder

    dCoder Newbie

    Try using BigDecimal instead of Double.
     
  5. Doug Simmons

    Doug Simmons Newbie

    I love this thread. Thanks. :)
     
  6. meackerman

    meackerman Newbie

    even BigDecimal isn't perfect, but it works much better. We typically don't worry about the rounding error too much since we usually round to a particular level of precision when we display a number to the user, but that doesn't work so well with a calculator app.

    I've written write code that'll take a number like 2.59079999999998 and figure out its really 2.5908 for the cases where we don't know the level of precision beforehand.
     
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