Locally declared variables can not be inspected

Question

Sometimes when I am debugging code in Eclipse it happens that although I can see and inspect class member variables without any difficulty I am unable to inspect the values of variables declared locally within functions. As an aside, any parameters to the current function lose their 'real' names and instead one sees their values listed in the Variables window as arg0, arg1, arg2, etc but at least the values are visible.

This is occurring at present in relation to classes defined within the core JDK. I have verified that the installed and current JRE is a JDK.

Is anybody able to shed some light on this behaviour?

Answer 1

Apparently, the answer is:

the rt.jar that ships with the JDK (where the core Java classes live) is not compiled with full debug information included in the .class files, so the debugger does not have local variable info.

Unfortunately, this is not something that Eclipse can do anything about - all debuggers will have the same problem with JDK core classes.

The release note of eclipse3.4 specify:

Missing debug attributes
The debugger requires that class files be compiled with debug attributes if it is to be able to display line numbers and local variables. Quite often, class libraries (for example, "rt.jar") are compiled without complete debug attributes, and thus local variables and method arguments for those classes are not visible in the debugger.

Answer 2

It used to be that you can get debug rt.jar from http: //download.java.net/jdk6/binaries/, but not any more.

So building your own rt.jar with -g seems to be the only option now. It's very simple: just use javac and jar from your JDK.

• mkdir \tmp; mkdir \tmp\out
• Extract src.zip in JDK installation directory to tmp\src
• cd src
• find -name *.java > files.txt
• javac -verbose -g -d \tmp\out -J-Xmx512m -cp "<jdk>\jre\lib\rt.jar";"<jdk>\lib\tools.jar" @files.txt
• cd \tmp\out; jar cvf rt.jar *

If you use Eclipse, you don't need -Xbootclasspath/p:, instead just put your debug jar to Bootstrap Entries before JRE in launch configuration.