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PODoubles with constraints in Java?
 

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  1. PODoubles with constraints in Java?
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    <p>I am porting a legacy Python system to Java. I'm a python developer primarily so this question concerns how I might take an unsatisfactory pattern in the original Python system but do it better in my Java version. </p> <p>A system I'm working on deals with prices of products. All products have prices > 0.0.</p> <p>In the orginal system all prices are represented as Python float objects (roughly like a Java Double). Functions which operate on these prices typically begin with a bunch of asserts to check that the range of the prices are sensible. Since there are a lot of functions there are a lot of assertions which become very repetitive after a while. </p> <p>These assertions are better than nothing but it would be far better to throw an error the instant that something tried to create a negative price, since that's where the fault lies.</p> <p>It occurred to me that I might do better in my re-implementation by inventing a new type of numberish thing which behaves exactly like a Double in all ways except that it cannot be constructed with a negative value. If I had such an object then I could rely on Java's type system and not need to write so many asserts.</p> <p>Other than that (to begin with) it will obey all the normal rules of arethmatic - it will be a subclass of Double. </p> <p>Later on I might extend this class by adding features that embrace more features of real-world money, e.g. preventing fractions of pennies. That's not actually needed in my initial version, but I'd like any pattern I adopt to accomodate this sort of development over the next few months.</p> <p>Is this kind of pattern considered acceptable to a Java developer? Is there a better way to preserve the flexibility of having number-like objects but constraints on their possible values?</p>
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    1. USSalim Fadhley
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    1. COWell it is surely not a good idea to store prices in a `float` or `double` type fields. What you should always use is decimal type like `BigDecimal` in Java.
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      1. USJagger
    2. COHave you considered using BigDecimal or BigInteger? Look at [this](http://stackoverflow.com/questions/5411637/bigdecimal-check-value-is-within-double-range) question to see it it fits your needs.
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      1. PODoubles with constraints in Java?
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    3. COAdding from gpeche: Double cannot be extended because it is final.
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      1. USThorsten S.
 

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