Paul Werbicki Supervisor: Dr. Robert C. Kremer Developing Applications with Multiple Programming Languages – an Investigation using C++ and Java Paul Werbicki Supervisor: Dr. Robert C. Kremer Department of Computer Science University of Calgary

Agenda Problem Statement Problem Scope Integration Approaches A Hybrid Approach The Java/C++ Class Library Investigation Results and Current Limitations Contributions and Future Work

Problem Statement How can a single object-oriented application written in one programming language integrate code from another language? What approaches have been used to integrate multiple programming languages? What requirements should an approach meet in order to provide benefit to a developer? To what level is it possible to integrate separate languages, and what limitations currently exist?

Problem Scope Programming languages used include: C++, Java and Visual Basic (.NET) Integration occurs between native and virtual programming languages C++ integrating Java Java integrating C++ Visual Basic integrating Java Integration occurs between programming languages contained in a single application running within a single process Process App Java C++

Integration Approaches Library JNI Enhancement Libraries (MIIK Ltd., 2005; Trewhella, 2002; Gabrilovich & Finkelstein, 2001) Simplifies use of the Java Native Interface (JNI) Reduces developer effort by encapsulating common functionality Proxy Classes (Gamma, Helm, Johnson, & Vlissides, 1995) Transforms code from one programming language to another, providing a level of seamless integration Proxy Class

Integration Approaches Remote Procedure Calls (Intrinsyc Software International Inc., 2005; JNBridge LLC, 2005) Uses Inter-Process Communication and Wire Protocols such as Distributed Component Object Model (DCOM) and Common Object Request Broker Architecture (CORBA) “Out-of-process” only solution, not usable within the context of a single application running within a single process Requires additional resources such as an RPC server App RPC

Microsoft JVM JVM Microsoft directly modified the Java Virtual Machine (JVM) to support programming language integration (Gilbert, 2004) Raw Native Interface and J/Direct Java and Component Object Model (COM) Callable Wrappers Sun vs. Microsoft Microsoft’s JVM enhancements failed to deliver a Java-compatible product Sun’s litigation forced Microsoft to remove the JVM from the market, to be replaced by their .NET framework

A Hybrid Approach Combines the benefits of the Microsoft approach without modifying the JVM Uses COM as an intermediate interface between C++ and Java Implements as an Enhancement Library Provides a Proxy Compiler Tool for greater level of programming language syntax integration COM Library JNI Proxy

Java/C++ Class Library Written in C++ and Java (using the JNI) Based on the object-oriented programming paradigm Uses standard COM interfaces as the contract between programming languages Performs marshalling of all scalar types and most complex types Proxy Compiler Tool allows secondary programming language code to conform to the syntax of the primary language Code A Code B COM Library

Investigation The Collaborative Agent System Architecture (CASA), A Multi Agent System (MAS) written in Java, was integrated with specialized devices using C++ and Visual Basic in an intelligent environment X10 Physical Device Agent Voice-Activated Light Switch Web-Based Device Console Accesses SMARTHOME API to control X10 devices (Section 5.3.1) Sends voice- based commands using CASA (Section 5.3.2) Java Queries physical devices using CASA to display in web-based interface (Section 5.3.3) C++ Visual Basic

Results The Java/C++ Class Library successfully integrated multiple programming languages in most scenarios Allowed the reuse of existing code without modification Existing software with well-defined interfaces provided the highest level of integration Inheritance across the native/virtual boundary required the use of a delegate class Interface Sub- system

Inheritance Across the Native/Virtual Boundary CMyAgent inherits from casa.Agent, overrides handleMessage() Java CMyAgent casa.Agent (C++ Proxy) JavaCOM casa.Agent CASA Agent() CreateObject() AllocObject() regsiterWithLAC() joinCD() sendMessage() sendCDMessage() handleMessage() ~Agent() Release() Message is received from another agent Message is received by casa.Agent::handleMessage, should be received by CMyAgent::handleMessage. Message does not propagate across the Native/Virtual Boundary.

Contributions The Java/C++ Class Library is a combination of multiple integration approaches that is advantageous in many development scenarios Provides a similar level of integration by containing the JVM, interfacing with it through the JNI The complete source code is available to help with research projects that require applications written in multiple languages Provides a basis on which further research into fully supporting the object-oriented programming paradigm may occur

Future Work To fully support native/virtual inheritance an object-oriented interface is required, as the JNI provides only a procedural approach Sun’s Java Research License offers the possibility of modifying the JVM to support such an interface without using COM This interface could then be submitted to the Java Community Process (JCP) as a next generation interface of the JNI

References Gabrilovich, E., & Finkelstein, L. (2001, January). JNI - C++ Integration Made Easy. C/C++ Users Journal, 10-21. Gilbert, H. (2004). The Tragedy of Microsoft and Java. New Haven, CT, USA: Yale University. MIIK Ltd. (2005). JNIWrapper. Kharkov, Ukraine: MIIK Ltd. Trewhella, P. E. (2002). JNI++: SourceForge.net.

Additional Slides Java Native Interface (2.1.2.2, pg. 11) Component Object Model (4.1, pg. 38) Class Diagram (4.2, pg. 45) Ambient Intelligent Environment Diagram Inheritance Expected (5.3.3, pg. 77) vs. Actual (5.4.2, pg. 83) Delegate Class (5.3.2, Pg. 75)

Java Native Interface (2.1.2.2, pg. 11) Based on the Netscape Java Runtime Interface (JRI) Unlike Microsoft RNI and COM, it is not vendor specific Standard native interface to the JVM Used for embedding JVM into other applications Avoids restrictions on JVM implementations Binary compatibility between Java Virtual Machines Exposes JVM internals Remains open to future development

Java Native Interface (2.1.2.2, pg. 11) cont’d Procedural-based library: Invocation functions Type and method mapping functions Object and scalar array manipulation functions Fields and methods are accessed by ID Provides access to object references, garbage collection and exception handling

Component Object Model (4.1, pg. 38) Component-based approach to software development Allows components from independent vendors to work together Allows components to be upgraded without recompiling the entire project Programming language independence Host environment independence

Component Object Model (4.1, pg. 38) cont’d Procedural/interface-based library Component/interface discovery functions Standard interfaces for component/interface/method discovery Dynamic interfaces for late-binding to interfaces/methods at run-time vs. early-binding during compile-time Provides binary-compatibility Methods are grouped into interfaces which are then grouped into components Components and interfaces are uniquely identified Dynamic discovery of interfaces and invocation of methods

Java/C++ Class Library (4.2, pg. 45)

Ambient Intelligent Environment

Inheritance Expected (5.3.3, pg. 77) vs. Actual (5.4.2, pg. 83)

Delegate Class (5.3.2, pg. 75)