JetBrains's IntelliJ IDEA uses a wrapper around the Java compiler, named javac2, to provide additional support for compiling .form files produced by the IDE, and for processing @Nullable and @NotNull annotations. It is naturally supported inside IDEA itself, and also by Apache Ant. However, other build systems like Gradle do not support it out of the box. Supporting it is useful - e.g. if you wanted to run a continuous integration server, which means you cannot use IDEA for building, and want it to compile your forms. Also, it could be useful if other developers on the same project used a different IDE.