Java-Hate on Insignificant Bits

Mavened.

Thu, 13 Dec 2012 17:03:51 +0000

So, I’m applying a one line patch to a Java package, and oh yes, it needs maven. Hooray!

$ apt-cache depends --recurse maven | grep Depends |
     grep -v '<' | egrep lib.*java | sort | uniq | wc -l
203
[... start build and watch maven download another pile ...]
$ find ~/.m2 -name *pom | wc -l
851

I find it hard to believe that there are that many useful libraries in the world.

Orders of magnitude

Fri, 30 Mar 2012 11:53:47 +0000

I had a Hadoop map-reduce job that kept timing out, which led to this interesting discovery:

$ time ./json-parser-test.py

real	0m0.205s
user	0m0.152s
sys	0m0.032s

$ time ./json-parser-test-no-speedups.py

real	0m2.069s
user	0m2.044s
sys	0m0.024s

$ time jython ./json-parser-test-no-speedups.py

real	79m59.785s
user	80m23.709s
sys	0m14.441s

Moral: use Java-based JSON libraries if you have to use Jython and JSON. Also, Java sucks.

On static in Java

Sun, 30 Jan 2011 00:52:06 +0000

In C, scoping rules aside, the following are pretty much the same:

static int x[] = { /* ... */ };
int foo()
{
    /* do something with x */
}

and

int bar()
{
    static int x[] = { /* ... */ };
    /* do something with x */
}

The static array x will go into the .data section of the executable. When the OS loads the executable into memory, it will ensure that the values for x are set in the appropriate place (e.g. by mapping its disk page to the virtual address in the ELF headers). In the second case, x is given some alias to avoid symbol conflicts.

JNIs and ABIs

Wed, 11 Aug 2010 03:16:11 +0000

For a recent task at work, I had a compelling reason to break out of the Java jail and do some “real programming” in C. Unfortunately, said C-language bits were to be run on the Windows platform. I had a stripped DLL (no source) for manipulating USB cameras and an API document to work with, and a plan to duct tape this all together with JNI.

I’m not about to touch MSVC if I can help it, so I grabbed mingw packages for my platform and wrote up a small wrapper DLL to do the necessary JNI bridge. Here’s my attempt to archive the working recipe for the Google bots.

JBoss Hash

Mon, 04 Jan 2010 22:21:26 +0000

Here’s how to figure out the hashes of method names used by JBoss’ RMI invoker from the shell. The first two numbers in the method signature form the length of the string. Maybe there’s a better way to do the backrefs in sed, but you do need to swap them around.

$ echo $[`printf "0031ping(Ljava/lang/String;)V" |
    sha1sum |
    sed -e "s/(..)(..)(..)(..)(..)(..)(..)(..).*/0x87654321/g"`]

Don’t ask me why I figured that out.

sizeof()

Tue, 17 Feb 2009 21:50:00 +0000

Renaming your class variables to shorter names reduces your EJB network footprint. Finally, those people who said that removing vowels from variable names improved performance are vindicated! Ok, well they were correct already in Javascript, but that doesn’t count.

is-not-a

Tue, 17 Feb 2009 03:18:00 +0000

Let’s dump the last useful feature in Java. What castles in the sky are people building these days?

swing rant

Mon, 07 Jul 2008 14:56:00 +0000

Never ever write a Java gui application with the requirement that you check fields before letting the user tab off of them. What a nightmare! Your only two tools, without rewriting large parts of Swing yourself, are FocusListener and InputVerifier. FocusListener is great for the case when you have two such fields. Set up bad data in each field, then watch the focus traversal war as a focusLost() method reclaims the focus for one component, causing focusLost() in the other component to fire. Fun. Then you have InputVerifier, ostensibly designed for this very purpose. Ignoring the fact that buttons still fire without the verifier getting called, now you have the awesomeness of not knowing what the target component would be. Want to build a view with multiple fields that get validated as one? Good luck with that.

Meh

Tue, 13 May 2008 13:48:00 +0000

I’m playing with date conversions today, and again I’m struck by how much the Java Calendar should be held up as an example of the over-engineered API. Has anyone ever used anything besides the Gregorian calendar? They were so proud of it when it hit 1.1.

I should have two patches hitting kernel 2.6.26, one entirely cosmetic and one that fixes a real bug on Atheros wireless cards. Akpm did pick up the OMFS patchset so hopefully that will go in .27 timeframe, though the jury is still out on whether it hits mainline.

javac sucks

Thu, 10 Apr 2008 14:39:00 +0000

More evidence that javac is one of the dumbest compilers ever: public class Foo extends java.lang.Object{ public Foo(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."":()V 4: return public static void main(java.lang.String[]); Code: 0: aconst_null 1: instanceof #2; //class Foo 4: ifeq 15 7: getstatic #3; //Field java/lang/System.out:Ljava/io/PrintStream; 10: ldc #4; //String never! 12: invokevirtual #5; //Method java/io/PrintStream.println:(Ljava/lang/String;)V 15: return } Ok, I’ll give them a break – this probably never comes up in a real application.

Why I hate ant

Thu, 28 Feb 2008 20:04:00 +0000

$ strace -f ant > out.txt 2>&1
$ grep "stat.*java" out.txt  | wc -l
32933

WTF? No wonder our build times suck. I still have yet to hear a rationale for the existence of ant that had any more substance than “but make uses tabs!”

I hate you, Sun.

Thu, 24 Jan 2008 22:04:00 +0000

Is it too much to ask of a compiler that if it decides to blare warnings at you for no reason at all, that you can turn the !@#$ thing off? In a move that rivals the stupidity of certain gcc warnings, we have this:

[javac] file: java:519: warning: com.sun.rowset.CachedRowSetImpl is Sun proprietary API and may be removed in a future release

Well, hey that’s a nice heads-up to give me 600 times when compiling our tree. Let me go find the non-com.sun equivalent of that. Oh wait, there isn’t one! And, the freaking javadoc even tells you to do it that way. Okay, well, maybe @SuppressWarnings({"deprecation"}) will work? Nope, haha! Sigh. Time for a wrapper script.

I dislike Java.

Wed, 25 Oct 2006 19:00:00 +0000

Dear lazy web,

It would be nice if you could tell me a non-hacky way to do progress dialogs from within the event-dispatch thread in Swing, where all of our application logic happens to reside.

This doesn’t work: display modal dialog start worker thread (won’t run because event thread is blocked)

Nor does this: start worker thread display modal dialog (race condition hiding the dialog)

Joining in the event thread won’t work because it blocks updates. Using a non-modal dialog and passing the bottom-half of the rest of the event thread to the worker thread to execute at completion will work, but is obscenely messy. Or, one can spin in the beginning of the thread waiting for the modal dialog to appear to avoid the race condition, but that is still gross. One could subclass Dialog and have it also signal a condition variable once it blocks… ugh.