Modular programming

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Modular programming is a software design technique that emphasizes separating the functionality of a program into independent, interchangeable modules, such that each contains everything necessary to execute only one aspect of the desired functionality.[1] Conceptually, modules represent a separation of concerns, and improve maintainability by enforcing logical boundaries between components. Modules are typically incorporated into the program through interfaces.[2] A module interface expresses the elements that are provided and required by the module. The elements defined in the interface are detectable by other modules. The implementation contains the working code that corresponds to the elements declared in the interface.

Language support[edit]

Languages that formally support the module concept include Ada, Algol, BlitzMax, COBOL, Component Pascal, D, Erlang, F, Fortran, Haskell, IBM/360 Assembler, IBM RPG, Java (packages are considered modules in the JLS[3]—the package chapter does not mention modules and "superpackages", meant for Java 7 were meant to provide Java with module support. Also Project Jigsaw is now scheduled to provide modules for Java 9 ), MATLAB, ML, Modula-2, Modula-3, Morpho, Oberon, NEWP, Node.js, Object Pascal, OCaml, Pascal, Perl, PL/I, Python, PureBasic, and Ruby.[1] The IBM System i also uses Modules in CL, COBOL, and RPG when programming in the Integrated Language Environment (ILE). Modular programming can be performed even where the programming language lacks explicit syntactic features to support named modules. OSGI adds a module layer to the Java language.

Software tools can create modular code units from groups of components. Libraries of components built from separately compiled modules can be combined into a whole by using a linker.

Key aspects[edit]

With modular programming, concerns are separated such that modules perform logically discrete functions. No (or few) modules interact with other modules of the system; except in the sense that one module may use another module, to achieve its purpose. The desired module goal is to have no interaction between modules [other than that already stated].

Each module (which can contain a number of separate processes) works independently from another module. At the lowest module hierarchy, no other module is used; at the highest module hierarchy, there may be several layers of other modules used, before the top module achieves its purpose.

When creating a modular system, instead of creating a monolithic application (where the smallest component is the whole), several smaller modules are built (and usually compiled) separately so that, when composed together, they construct the executable application program. A just-in-time compiler may perform some of this construction "on-the-fly" at run time.

This makes modular designed systems, if built correctly, far more reusable than a traditional monolithic design, since all (or many) of these modules may then be reused (without change) in other projects. This also facilitates the "breaking down" of projects into several smaller projects. Theoretically, a modularized software project will be more easily assembled by large teams, since no team members are creating the whole system, or even need to know about the system as a whole. They can focus just on the assigned smaller task (this, it is claimed, counters the key assumption of The Mythical Man Month—making it actually possible to add more developers to a late software project—without making it later still).


Traditional programming languages have been used to support modular programming since at least the 1960s. Modular programming is a loosely defined concept with no official definition. It is, in essence, simply a programming technique[dubious ]. Exactly where "modularized" programming ends, and dynamically linked libraries or object-oriented programming starts in this context is subjective. It might be defined as the natural predecessor of OOP, or an evolutionary step beyond it, depending upon viewpoint.[citation needed][clarification needed]

See also[edit]


  1. ^ Jürgen Haas. "Modular programming". "Modular programming is a programming style that breaks down program functions into modules, each of which accomplishes one function and contains all the source code and variables needed to accomplish that function. Modular programming is a solution to the problem of very large programs that are difficult to debug and maintain. By segmenting the program into modules that perform clearly defined functions, you can determine the source of program errors more easily. Object-orientated programming languages, such as SmallTalk and HyperTalk, incorporate modular programming principles." 
  2. ^ Seif Haridi; Nils Franzén. "7. Modules and Interfaces". Mozart Documentation. "Modules, also known as packages, are collection of procedures and other values1 that are constructed together to provide certain related functionality. A module typically has a number of private procedures that are not visible outside the module and a number of interface procedures that provide the external services of the module." 
  3. ^ James Gosling, Bill Joy, Guy Steele, Gilad Bracha, The Java Language Specification, Third Edition, ISBN 0-321-24678-0, 2005. In the Introduction, it is stated "Chapter 7 describes the structure of a program, which is organized into packages similar to the modules of Modula." The word "module" has no special meaning in Java.