Lets you specify the Java platform compliance level. This setting currently only affects the handling of reserved keywords.

Choosing "J2SE 5.0" means that assert and enum will be recognized as reserved keywords.

Choosing "J2SE 1.4" means that only assert will be recognized as a reserved keyword.

Choosing "J2SE 1.3" means that the above mentioned strings are valid identifiers that can be used for variable and/or method names.

It is highly recommended to avoid strings that have become reserved keywords when targeting older Java releases, so you might always want to choose the most recent Java version here to enable future compatibility with recent releases.