Java – Why are some java libraries compiled without debugging information


I've noticed recently that there's a few java libs (the JDK, joda time, iText) that compile without some/all of the debugging information. Either the local variable info is missing, or the both the local variable info and line numbers are missing.

Is there any reason for this? I realise it makes compiled code larger but I don't believe that's a particular large consideration. Or is it just building with the default compile options?


Best Solution

The default compile options don't include debugging information, you must specifically tell the compiler to include it. There are several reasons why most people omit it:

  • Some libraries are used in embedded systems (like mobile phones). Until recently, every bit counted. Today, most mobiles come with more memory than all computers in 1985 had together ;)
  • When compiled with debugging active, the code runs 5% slower. Not much but again, in some cases every cycle counts.
  • Today's Senior Developers were born in a time when 64KB of RAM was enormous. Yesterday, I added another 2TB drive to my server in the cellar. That's 7 orders of magnitude in 25 years. Humans need more time to adjust.

[EDIT] As John pointed out, Java bytecode isn't optimized (much) anymore today. So the output of the class files will be the same for both cases (only the class file with debug information will be bigger). The code is optimized in the JIT at runtime which allows the runtime to optimize the code for the CPU, memory (amount and layout), etc.

The mentioned 5% penalty is when you run the code and add the command line options to allow a remote debugger to attach to the process. If you don't enable remote debugging, there is no penalty (except for class loading but that happens only once).