The Cafes

Happy 20th Birthday Java! Next year I’ll buy you a drink. InfoWorld has published some of my thoughts on the occasion, “Java at 20: How it changed programming forever”.

java.util.Arrays uses quicksort (actually dual pivot quicksort in the most recent version) for primitive types such as int and mergesort for objects that implement Comparable or use a Comparator. Why the difference? Why not pick one and use it for all cases? Robert Sedgewick suggests that “the designer’s assessment of the idea that if a programmer’s using objects maybe space is not a critically important consideration and so the extra space used by mergesort maybe’s not a problem and if the programmer’s using primitive types maybe performance is the most important thing so we use the quicksort”, but I think there’s a much more obvious reason.
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In my day job I work with a lot of very smart developers who graduated from top university CS programs such as MIT, CMU, and Chicago. They cut their teeth on languages like Haskell, Scheme, and Lisp. They find functional programming to be a natural, intuitive, beautiful, and efficient style of programming. They’re only wrong about one of those.
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Something I realized in the middle of an introductory course on cryptography when the instructor said the word “commutative” for the first time: N-bit strings with the operation XOR are an abelian group.
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Memo to self: when attempting to prove a theorem, and it just doesn’t seem to be working; don’t forget to search for counterexamples. The theorem may not actually be true.
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