Why does Eclipse warn about Java "unused variables" but javac does not?

Question

For the same code, Eclipse shows warnings about unused variables, but compiling with "javac" (v1.6) does not. Does Eclipse use a different compiler or parser? How can I get javac to show the same warnings?

Answer 1

Quote from JDT core (Eclipse's editor infrastructure)

JDT Core is the Java infrastructure of the Java IDE. It includes:

An incremental Java compiler. Implemented as an Eclipse builder, it is based on technology evolved from VisualAge for Java compiler. In particular, it allows to run and debug code which still contains unresolved errors.

It is the incremental Java compiler that shows the warning.

There are no ways to enable that warning in Sun/Oracle javac

Answer 2

From javadoc:

-Xlint Enable all recommended warnings. In this release, all available warnings are recommended.

And yes, eclispe use own compiler

Answer 3

This is part of the validation in eclipse. If you wanted your own rules similar to what eclipse does, you could use something like PMD.

http://pmd.sourceforge.net/rules/unusedcode.html

Answer 4

Eclipse uses its own compiler. You can enable/disable various messages by going to Window->Preferences->Java->Compiler->Errors/Warnings.

Answer 5

This is Eclipse own functionality.