InterfaceMayBeAnnotatedFunctional

Reports interfaces that can be annotated with @FunctionalInterface.

Annotating an interface with @FunctionalInterface indicates that the interface is functional and no more abstract methods can be added to it.

Example:

interface FileProcessor {
    void execute(File file);
  }

After the quick-fix is applied:

@FunctionalInterface
  interface FileProcessor {
    void execute(File file);
  }