TweetFollow Us on Twitter

Oct 01 Cover Story

Volume Number: 17 (2001)
Issue Number: 10
Column Tag: Software Engineering


by Paul E. Sevinc, Switzerland


Reuse is a key objective of software engineering. In our January 2001 article [15], we discussed how reuse is achieved by the use of patterns. To recap, we saw that patterns promote analysis, architecture, or design reuse, but never implementation reuse. A framework supplies the mechanisms that enforce a policy for interaction between software entities with open implementations [2]. As we shall see, frameworks always promote analysis, design, and implementation reuse, but not always architecture reuse.

In this article, we briefly review libraries and toolkits as a point of comparison for frameworks. Then we discuss in more detail object-oriented frameworks. Finally, we touch on the issue of black-box vs. white-box reuse.

Libraries and Toolkits

Szyperski [17, p. 134] notes that "[e]arly programming languages attempted to provide all functions that would ever be used in multiple programs. An explosion of built-in functions was the result. [...] Since then, there has been a clear tendency to take specific functionality out of languages, in favor of abstractional and structural features." The specific functionality that was taken out, as well as additional functionality, was put in libraries. (As explained at the end of this section, toolkits are just special types of libraries.) The evolution of Pascal over Modula-2 to Oberon [11] is but one witness of this tendency.

The primary purpose of software libraries is to provide software engineers with reusable pieces of code (i.e., implementation). The most common kinds of libraries are procedure libraries (also called function libraries) and class libraries.

The Mac Toolbox/Carbon [1] is an example of a procedure/function library. It is designed and implemented in a procedural fashion to be used with a procedural programming language such as Pascal or C. Note that it not only defines procedures/functions, but also data structures (i.e., RECORDs and structs).

The C++ Standard Library [16] is an example of a class library. It is designed and implemented in an object-oriented fashion to be used with an object-oriented programming language, namely C++. Just like C++ is not a purely object-oriented programming language (as opposed to Java for instance), but a hybrid programming language, the C++ Standard Library is not a pure class library. Rather, it is a library of libraries, some of which are class libraries.

Toolkits are simply class libraries whose classes are related [5]. An example is the Java Abstract Window Toolkit (AWT), a library of classes for graphical user interfaces (GUIs) [6].

Libraries vs. Frameworks

First of all, let us dispel a common misconception: frameworks are not exclusive to the realm of object orientation. Oberon microsystems, for instance, have an amazing component framework in their product line [10]. And numerous frameworks have been realized in a procedural programming language such as C. However, we have to add that in the latter case, procedure variables/function pointers are typically used to mimic polymorphism. That said, we nevertheless confine ourselves to object-oriented frameworks, nowadays the most typical kind of frameworks, in the next section.

Whatever the paradigm used, the key difference between libraries and frameworks lies in whether the client is in charge or not:

Figure 1: Library vs. Framework [9].

In procedural programming, the client of a procedure library develops the main procedure and calls library procedures at her own discretion (see Figure 1 left). In a similar manner, when using a class library, the user-defined classes are in control and determine the overall architecture of the system.

The opposite is the case when development is based on frameworks; the framework decides when the user's methods are invoked. Thus, there is an inversion of control; the framework incorporates the control logic [5, 12] (see Figure 1 right). (The way this is realized in object-oriented frameworks is explained in the next section.) This is called the Hollywood principle: "Don't call us, we'll call you!" [9] or the Greyhound principle: "Leave the driving to us." [2].

Examples: The Java Platform Math Class and Model-View-Controller in Swing

The Java Math class [6] defines mathematical functions (e.g., sin) as well constants (e.g., e) and as a whole is obviously a function library. Client code that invokes one of Math's methods relinquishes control only for a split second and does not have to worry about any side effects.

The Model-View-Controller (MVC) pattern [5, 9] depicted in Figure 2 underlies Java's Swing GUI elements [6]. In the case of a text field, for instance, the model manages the actual text in memory, the view displays the text on screen, and the controller determines the text's editability.

Figure 2: Components of the MVC [9].

We are not restricted to using the text field as is. Any of its three constituent parts can be replaced independent of the others by a subclass (e.g., the default controller in order to accept numerical characters only). That and the fact that the methods our subclass overrides are—or in a good design at least should be—invoked only by non-client code make the text field a framework.

Object-Oriented Frameworks

An object-oriented framework is a customizable implementation of software. It consists of a set of cooperating classes and has hot spots [9] (also called plug points [4]), which make the customization possible (see Figure 3).

Figure 3: Framework [9].

Hot spots are abstract, or at least non-final, classes. Through factory, template and hook methods [5], the framework invokes the methods on the subclasses of the hot spots (see Figure 4). But it maintains overall control and makes sure that certain core tasks are fulfilled.

Figure 4: HotSpot [9].

Example: JUnit

JUnit is a framework for unit testing in Java [7]. Its original authors are Kent Beck and Erich Gamma, but it is maintained by an open community of software engineers. JUnit's four core types are partially depicted in Figure 5.

Clients of the framework subclass TestCase to add one or more methods that actually conduct tests. That is, TestCase is a hot spot. The three TestCase methods shown in italic are not really abstract: setUp and tearDown are empty hook methods invoked by the template method run before and after runTest, respectively. And runTest's default implementation invokes the client-added test method designated by the fName field using reflection.

Figure 5: JUnit Extract (adapted from [3]).

Let us discuss the use of the fName field a little bit more. As we already mentioned, a TestCase subclass can define more than one test method to test different aspects of a class or a set of classes. Typically, runTest invokes only one client-added test method (because setUp and tearDown should be invoked before and after every test method, but only by run in order to keep the design clean). Therefore, the TestCase subclass has to be further subclassed to override runTest for each test method. Alternatively, the TestCase subclass is not subclassed further. Instead, fName is defined to contain the name of different test methods for different instances. The latter approach is obviously simpler (albeit less type safe). (Using reflection in this way within an object-oriented framework allows for what could be considered "run-time parameterizable hot-spots".)

Beck and Gamma [3] treat the core design of the JUnit framework (using the language of design patterns) in more detail.

Application and Domain-Specific Frameworks

Frameworks can be domain-specific. FEMO, for instance, is a framework for multiobjective optimization with genetic algorithms [13]. Applications that make use of FEMO relinquish control during optimization runs, but FEMO does not impose any architecture on the application as a whole. Therefore, FEMO promotes analysis, design, and implementation reuse: analysis of the domain, and design and implementation of the classes.

An application framework is a standard program that takes care of window management, menu handling, opening & saving documents, etc., but that has to be extended by the programmer to give them content. Mössenböck [9] calls this programming by difference. Metrowerks' PowerPlant [8] is a typical application framework and as such defines the overall architecture of every PowerPlant-based application.

Black-Box vs. White-Box Reuse

A black-box framework hides its implementation from its clients whereas the implementation of a white-box framework is visible to—and possibly modifiable by—its clients. A glass-box framework is a white-box framework whose implementation is not modifiable. [18] (Note that, rather confusingly, frameworks are sometimes designated as white-box as soon as they emphasize implementation inheritance over object composition [17], whether the implementation is actually visible to the client or not.)

Black-box reuse is preferable over white-box reuse. With the former, when (part of) the framework is replaced by a new release whose interface and specification have not changed, client code should not break. With the latter, the implementation may have to be studied anew, since at least informally it was part of the contract.

Listing 1

method( Type parameter )
   throws IllegalArgumentException
   if ( parameter == null || !inRange( parameter ) ) {
      throw new IllegalArgumentException();

For example, after studying its source code, some clients of the white-box method method in Listing 1 might rely on NullPointerExceptions (which are unchecked exceptions in Java and thus need not be declared in the exception specification) never being thrown. In a future version, method no longer checks for null references (see Listing 2), which—let us assume—it never advertised to do anywhere in its formal documentation in the first place. At compile time, all of the existing clients will compile just fine. At run time, however, some might now behave erroneously.

Listing 2

method( Type parameter )
   throws IllegalArgumentException
   if ( !inRange( parameter ) ) {
      throw new IllegalArgumentException();

To Probe Further

Mössenböck's Objektorientierte Programmierung in Oberon-2 [9] is an excellent book on object orientation in general. The latest edition features a chapter on frameworks. Unfortunately, this edition has never been translated to English.

Gamma et al.'s Design Patterns [5] is first and foremost a book on, well, design patterns. Nevertheless, it also quickly introduces frameworks and discusses the important relationship between patterns and frameworks.

Szyperski's Component Software [17] is a seminal work on component orientation. It features a chapter discussing reuse in general, including a concise treatment of frameworks.


This article is partly based on a chapter in my M.S. thesis [14] that was proofread and commented on by Prof. Dr. Rachid Guerraoui, Dr. Jean-Philippe Martin-Flatin, Luc Girardin, and Dani Seelhofer.

I would like to thank the contributing reviewers for this article, Nate Little and Peter "Primetime" Taylor from Trilogy Software, Inc.


  • [1] Apple Computer, Inc. Carbon Developer Documentation. Home Page. Located at
  • [2] B. Appleton. "Patterns and Software: Essential Concepts and Terminology". Available at
  • [3] K. Beck and E. Gamma. "JUnit: A Cook's Tour". Java Report, Vol. 4, No. 5, May 1999.
  • [4] D.F. D'Souza and A.C. Wills. Objects, Components, and Frameworks with UML: The Catalysis Approach. Addison-Wesley, Reading (Massachusetts), 1999.
  • [5] E. Gamma, R. Helm, R. Johnson, and J. Vlissides. Design Patterns: Elements of Reusable Object-Oriented Software. Addison-Wesley, Reading (Massachusetts), 1995.
  • [6] C.S. Horstmann and G. Cornell. Core Java: Fundamentals. Sun Microsystems Press, Palo Alto, 5th edition 2001.
  • [7] JUnit, Testing Resources for Extreme Programming. Home Page. Located at
  • [8] A. Montgomery. "First Steps". MacTech Magazine, Vol. 17, No. 4, April 2001.
  • [9] H. Mössenböck. Objektorientierte Programmierung in Oberon-2. Springer, Heidelberg, 3rd edition 1998.
  • [10] Oberon microsystems, Inc. BlackBox Component Builder. Home Page. Located at
  • [11] M. Reiser and N. Wirth. Programming in Oberon: Steps beyond Pascal and Modula. Addison-Wesley, Reading (Massachusetts), 1992.
  • [12] S.R. Schoch. Classical and Object-Oriented Software Engineering: With UML and Java. McGraw-Hill, Boston, 4th edition 1999.
  • [13] P.E. Sevinç. Ein C++-Framework für die Mehrzieloptimierung mit genetischen Algorithmen. Semester Thesis, Swiss Federal Institute of Technology Zurich, January 1999.
  • [14] P.E. Sevinç. Design Patterns for the Management of IP Networks. M.S. Thesis, Swiss Federal Institute of Technology Zurich, February 2000.
  • [15] P.E. Sevinç. "Patterns". MacTech Magazine, Vol. 17, No. 1, January 2001.
  • [16] B. Stroustrup. The C++ Programming Language. Addison-Wesley, Reading (Massachusetts), 3rd edition 1997.
  • [17] C. Szyperski. Component Software: Beyond Object-Oriented Programming. Addison-Wesley, Reading (Massachusetts), 1998.
  • [18] C. Szyperski. "Components and Objects Together". Software Development, Vol. 7, No. 5, May 1999. Available at

Paul E. Sevinç is back in Europe after spending three fantastic months in Austin, Texas going through Trilogy University, the corporate boot camp of Trilogy Software, Inc. You can reach him at


Community Search:
MacTech Search:

Software Updates via MacUpdate

Spotify - Stream music, creat...
Spotify is a streaming music service that gives you on-demand access to millions of songs. Whether you like driving rock, silky R&B, or grandiose classical music, Spotify's massive catalogue puts... Read more
Google Chrome 54.0.2840.71 - Modern and...
Google Chrome is a Web browser by Google, created to be a modern platform for Web pages and applications. It utilizes very fast loading of Web pages and has a V8 engine, which is a custom built... Read more
HoudahSpot 4.2.6 - Advanced file-search...
HoudahSpot is a powerful file search tool. Use HoudahSpot to locate hard-to-find files and keep frequently used files within reach. HoudahSpot will immediately feel familiar. It works just the way... Read more
Yummy FTP Pro 1.11.11 - $29.99
Yummy FTP Pro is an advanced Mac file transfer app which provides a full-featured professional toolkit combined with blazing speeds and impeccable reliability, so whether you want to transfer a few... Read more
Shimo - VPN client – for everyon...
Shimo is the most versatile VPN client for OS X and it enables really everybody to master secure network. It supports more protocols than any other VPN application out there! CiscoVPN, AnyConnect,... Read more
Dash 3.4.0 - Instant search and offline...
Dash is an API documentation browser and code snippet manager. Dash helps you store snippets of code, as well as instantly search and browse documentation for almost any API you might use (for a full... Read more
AirRadar 3.1.9 - $9.95
With AirRadar, scanning for wireless networks is now easier and more personalized! It allows you to scan for open networks and tag them as favourites or filter them out. View detailed network... Read more
Printopia 2.1.22 - Share Mac printers wi...
Run Printopia on your Mac to share its printers to any capable iPhone, iPad or iPod Touch. Printopia will also add virtual printers, allowing you to save print-outs to your Mac and send to apps.... Read more
SteerMouse 5.0 - Powerful third-party mo...
SteerMouse is an advanced driver for USB and Bluetooth mice. It also supports Apple Mighty Mouse very well. SteerMouse can assign various functions to buttons that Apple's software does not allow,... Read more
Alarm Clock Pro 10.2.5 - $19.95
Alarm Clock Pro isn't just an ordinary alarm clock. Use it to wake you up in the morning, send and compose e-mails, remind you of appointments, randomize the iTunes selection, control an internet... Read more

Latest Forum Discussions

See All

Game of Dice is now available on Faceboo...
After celebrating its anniversary in style with a brand new update, there’s even more excitement in store for Game of Dice has after just being launched on Facebook Gameroom. A relatively new platform, Facebook Gameroom has been designed for PC... | Read more »
4 addictive clicker games like Best Fien...
Clickers are passive games that take advantage of basic human psychology to suck you in, and they're totally unashamed of that. As long as you're aware that this game has been created to take hold of your brain and leave you perfectly content to... | Read more »
Smile Inc. Guide: How not to die on the...
As if Mondays weren't bad enough, at Smile Inc. you have to deal with giant killer donuts, massive hungry staplers, and blasting zones. It's not exactly a happy, thriving work environment. In fact, you'll be lucky to survive the nine to five.... | Read more »
Oh...Sir! The Insult Simulator (Games)
Oh...Sir! The Insult Simulator 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: | Read more »
WitchSpring2 (Games)
WitchSpring2 1.27 Device: iOS Universal Category: Games Price: $3.99, Version: 1.27 (iTunes) Description: This is the story of Luna, the Moonlight Witch as she sets out into the world. This is a sequel to Witch Spring. Witch Spring 2... | Read more »
4 popular apps getting a Halloween makeo...
'Tis the season for all things spooky. So much, so, in fact, that even apps are getting into the spirt of things, dressing up in costume and spreading jack o' lanterns all about the place. These updates bring frightening new character skins, scary... | Read more »
Pokémon GO celebrates Halloween with can...
The folks behind Pokémon GO have some exciting things planned for their Halloween celebration, the first in-game event since it launched back in July. Starting October 26 and ending on November 1, trainers will be running into large numbers of... | Read more »
Best Fiends Forever Guide: How to collec...
The fiendship in Seriously's hit Best Fiends has been upgraded this time around in Best Fiends Forever. It’s a fast-paced clicker with lots of color and style--kind of reminiscent of a ‘90s animal mascot game like Crash Bandicoot. The game... | Read more »
5 apps for the budding mixologist
Creating your own cocktails is something of an art form, requiring a knack for unique tastes and devising interesting combinations. It's easy to get started right in your own kitchen, though, even if you're a complete beginner. Try using one of... | Read more »
5 mobile strategy games to try when you...
Strategy enthusiasts everywhere are celebrating the release of Civilization VI this week, and so far everyone seems pretty satisfied with the first full release in the series since 2010. The series has always been about ultra-addictive gameplay... | Read more »

Price Scanner via

Macs’ Superior Enterprise Deployment Cost Eco...
IBM’s debunking of conventional wisdom and popular mythology about the relative cost of using Apple Mac computers as opposed to PCs running Microsoft Windows at the sixth annual Jamf Nation User... Read more
12-inch WiFi Apple iPad Pros on sale for $50-...
B&H Photo has 12″ WiFi Apple iPad Pros on sale for $50-$70 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 12″ Space Gray 32GB WiFi iPad Pro: $749 $50 off MSRP -... Read more
Apple refurbished 12-inch 128GB iPad Pros ava...
Apple has Certified Refurbished 12″ Apple iPad Pros available for up to $160 off the cost of new iPads. An Apple one-year warranty is included with each model, and shipping is free: - 32GB 12″ iPad... Read more
Apple refurbished iPad minis and iPad Air 2s...
Apple recently dropped prices on several Certified Refurbished iPad mini 4s and 2s as well as iPad Air 2s. An Apple one-year warranty is included with each model, and shipping is free: - 16GB iPad... Read more
MacHTTP-js Preview Full-featured Web Server f...
MacHTTP.Org has released MacHTTP-js Preview for macOS, a full-featured Web server for 21st Century desktops and servers. MacHTTP-js is a modern take on the classic stand-alone, desktop computer Web... Read more
Samsung Galaxy Tab A 10.1 with S Pen Makes US...
Samsung Electronics America, Inc. has announced the release of the Galaxy Tab A 10.1 with S Pen in a highly mobile, lightweight tablet. “With an embedded S Pen, consumers can discover more ways to... Read more
13-inch 2.5GHz MacBook Pro (Apple refurbished...
Apple has Certified Refurbished 13″ 2.5GHz MacBook Pros available for $829, or $270 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz MacBook Pros... Read more
27-inch iMacs on sale for up to $220 off MSRP
B&H Photo has 27″ Apple iMacs on sale for up to $200 off MSRP including free shipping plus NY sales tax only: - 27″ 3.3GHz iMac 5K: $2099 $200 off MSRP - 27″ 3.2GHz/1TB Fusion iMac 5K: $1899.99 $... Read more
13-inch 2.5GHz MacBook Pro available for $927...
Overstock has the 13″ 2.5GHz MacBook Pro available for $926.99 including free shipping. Their price is $172 off MSRP. Read more
Apple refurbished 2015 13-inch MacBook Airs a...
Apple has Certified Refurbished 2015 13″ MacBook Airs available starting at $759. An Apple one-year warranty is included with each MacBook, and shipping is free: - 2015 13″ 1.6GHz/4GB/128GB MacBook... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Software Engineering Intern: UI Applications...
Job Summary Apple is currently seeking enthusiastic interns who can work full-time for a minimum of 12-weeks between Fall 2015 and Summer 2016. Our software Read more
Security Data Analyst - *Apple* Information...
…data sources need to be collected to allow Information Security to better protect Apple employees and customers from a wide range of threats.Act as the subject Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 52812872 Houston, Texas, United States Posted: Oct. 18, 2016 Weekly Hours: 40.00 **Job Summary** As an Apple Solutions Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.