Tom Ball's Blog

Get Medieval On Your Code

In the past few years, Java has finally started to catch up with C on this front. Third-party static checkers like FindBugs and PMD are now freely available and are easily integrated into a build. In Java 5 the javac compiler added the -Xlint option with several types of checks, which were significantly expanded in Java 6. The Jikes compiler has a similar option called pedantic compilation (+P). All of these tools allow you to enable/disable different types of tests, and unless you strongly disagree with certain tests I recommend that you turn on all the warnings you can.

Sometimes you need to suppress one or more warnings for a specific block of code. Java 5 introduced the SuppressWarnings annotation to enable you to do this, but javac ignored it in that release; happily, it is now recognized in Java 5, update 6 (1.5_06). One big advantage of globally checking for a type of potential error and suppressing it in specific places is that the SuppressWarnings annotation serves as documentation that you really intended to do this questionable practice. For example, Jackpot's parser outputs a big switch statement for a rule set, which is optimized using case statement fall-through. Since fall-though can be a frequent source of bugs, Jackpot is tested with javac's fall-through checking and with a @SuppressWarnings("fallthrough") for this specific method -- that way if there are fall-through bugs elsewhere they will be flagged. Turning warnings into build-stopping errors has also been enabled in Java 6 via javac's hidden -Werror flag (just like the C compiler's). Jikes has the +Z2 flag to do this, and recently it added a -Werror equivalent to be command-compatible with javac.

For NetBeans projects, it is easy to set these flags by right-clicking on the project, selecting its properties, clicking on the Compiling panel and putting them in the "Additional Compiler Options" field. It can be a pain changing all of your Ant build files to do this, however. You can set this property globally, however, because NetBeans projects have a javac.compilerargs property hiding in the nbproject/build-impl.xml file we can use. To set this for all projects which have this property, add this line to $HOME/.antrc (which probably doesn't exist):

ANT_ARGS='-Djavac.compilerargs="-Xlint:all -Werror"'

Separate static checker tools can be integrated into your build as well. Ant tasks are available for both FindBugs and PMD. Both tools have a failOnError parameter which can be set true so the build stops if a warning is issued. Both of these tools support the SuppressWarnings annotation, too.

Now, those of you who are really hard-core will point out there are many other ways you can stop coddling your build and make it cough up its bugs. You are right, and in future blog postings I'll investigate other ways to get medieval on your code.

Comments

• @SuppressWarnings has worked in Sun's 1.5 for about a year now (update 6, IIRC).

  Posted by: tackline on November 20, 2006 at 03:33 PM

• Just wanted to mention - the latest FindBugs-Plugin for NetBeans can be download from here - https://sqe.dev.java.net/updatecenters/nbheaven-updatecenter.xml

  A even better integration is already underway - sqe.dev.java.net - will be the succesor, with integration of a lot of tools.

  Posted by: sven on November 20, 2006 at 04:06 PM

• The SQE project looks very cool, thanks for the link.

  Posted by: tball on November 20, 2006 at 04:20 PM

• Tips and comments:

  If you do not use Java serialization, you will be better off with

  
  -Xlint -Xlint:-serial

  
  In NB 6.0 builds with the new javac (i.e. daily builds and M5+), set in your netbeans.conf:

  
  -J-Dorg.netbeans.api.java.source.JavaSource.USE_COMPILER_LINT=true

  
  This will show warnings in the editor stripe, which is really nice. Hopefully soon the IDE will pick up background compiler flags from your project settings, so this will not be necessary.

  @SuppressWarnings("deprecation") may not yet work correctly on fields of deprecated type. A filed bug.

  NetBeans module projects do honor javac.compilerargs, since 5.0u1/5.5.

  Posted by: jglick on November 21, 2006 at 09:30 AM

• I edited the entry to fix the noted errors. Thanks for the feedback.

  Posted by: tball on November 21, 2006 at 11:48 AM

• I can't agree with you more on all this. I've been using NetBeans 5.5 lately and use the -Xlint:all -Werror, plus PMD, plus findbugs,, plus Junit tests, NetBeans Code formatting, NetBeans Fix Imports, and the NetBeans Auto Comment feature to make sure the javadoc comments are correct too. Although sometimes I wish there was one button that would do everything, on all files.

  Once the source is clean of warnings, it's easy to keep that way, and when anything goes wrong it's pretty obvious. I highly recommend using this kind of warning free approach.

  Findbugs in particular has found some very non-obvious bugs for me.

  -kto

  Posted by: kellyohair on December 01, 2006 at 10:59 AM

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