Force the creation of a new file

The point is to avoid contamination between must-be-compiled-separately files

Property definitions

nitc $ JavaCompiler :: new_file
	# Force the creation of a new file
	# The point is to avoid contamination between must-be-compiled-separately files
	fun new_file(name: String): JavaCodeFile do
		var file = new JavaCodeFile(name)
		files.add(file)
		return file
	end
src/compiler/java_compiler.nit:257,2--263,4