Why java.util.Arrays uses Two Sorting Algorithms

Saturday, March 30th, 2013

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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Why Functional Programming in Java is Dangerous

Sunday, January 20th, 2013

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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1% Problems

Sunday, July 22nd, 2012

I hate 1% problems. No this isn’t an OWS slogan. I’m thinking of those code issues that really aren’t a problem 99% of the time, but when they bite, they’re really hard to debug and they cause real pain. Several common cases in Java:

  1. Using java.util.Date or java.util.Calendar instead of JodaTime.
  2. Not specifying a Locale when doing language sensitive operations such as toLowerCase() and toUpperCase().
  3. Not escaping strings passed to SQL, XML, HTML or other external formats.

What I hate most is that it’s really, really hard to convince other developers that these are problems they should take seriously. (more…)

Could not load a dependent class com/jcraft/jsch/Logger

Friday, June 25th, 2010

Have you ever seen an Ant error message like this?

BUILD FAILED
/Users/elharo/Projects/XOM/build.xml:545: Problem: failed to create task or type scp
Cause: Could not load a dependent class com/jcraft/jsch/Logger
       It is not enough to have Ant's optional JARs
       you need the JAR files that the optional tasks depend upon.
       Ant's optional task dependencies are listed in the manual.
Action: Determine what extra JAR files are needed, and place them in one of:
        -/opt/ant/lib
        -/Users/elharo/.ant/lib
        -a directory added on the command line with the -lib argument

Do not panic, this is a common problem.
The commonest cause is a missing JAR.

This is not a bug; it is a configuration problem

As usual, the ant error message is completely unhelpful, though for once it’s at least technically correct. (Most of the time when ant says, “This is not a bug; it is a configuration problem”, it is in fact a bug and not a configuration problem.) Here’s what’s really happening.
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Internal and External Exceptions

Saturday, July 21st, 2007

Perhaps the continuing confusion over the difference between checked and runtime exceptions in Java is because we haven’t named them properly. Mosts texts and teachers, including myself, have traditionally focused on how and when you handle the exceptions (compile time or runtime) rather than on what causes each. I propose a modification, not in code, but in terminology and teaching. Specifically I think we should should start calling checked exceptions “external exceptions” and runtime exceptions “internal exceptions”.
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