If you can’t inspect a method argument (or local variable) object using Expressions/Watch/Inspect … Be creative and try Eclipse debug view -> Variables. It’s possible that local vars are not visible, but class fields are. Many fields of “this” are objects, so their fields are visible. Using a combination of fields you can often deduce the values of those local vars. Simple example — if a local var is set to someStaticMap.get( this.age%10 ), you can deduce that value.
Here’s the original context of this blog — During remote debugging one day, it turned out all these variables are non-viewable because we had built the project without including “debug information”. If your build-master allows, then the best solution is —
javac -g:vars # Local variable debugging information added to byte code in generated *.class files
Other eclipse users had the same issue — http://dev.eclipse.org/newslists/news.eclipse.tools.jdt/msg08356.html