For each ASN.1 production defined in the ASN.1 source file, a Java decode method may be generated. This method will decode an ASN.1 message into public member variables within the Java object.

As was the case for encode methods, a decode method is only generated if it is required to alter the default method in the base class. The Java model is built on inheritance from a set of common run-time base classes. These run-time classes contain default implementations of encode/decode methods that handle the encoding/decoding of the basic types. These default implementations include support for handling the universal tags associated with the types as defined in the X.680 standard.