The package specification is the first item in the file and is declared using the 'package' keyword. By default, this is set to the name of the ASN.1 module that is being compiled. However, this can be modified by using the –pkgpfx and – pkgname command line options. The –pkgpfx option adds the specified prefix before the module name. For example, if an ASN.1 module named 'Employee' is being compiled and '-pkgpfx test.' is specified on the command line, the package name in the generated source files would be 'test.Employee'. The –pkgname switch takes this a step further. It allows specification of the full package name. In the sample specification above, '-pkgpfx sample_ber.' was specified on the compiler command line.

Standard import statements are added for the ASN1C Java run-time classes and Java utility classes. Import statements may also be added for items imported from other ASN.1 modules if they don't exist within the package being generated.