Reuse is a major theme in software engineering practices. By reusing tried-and-tested components, the robustness of a new software system can be enhanced while reducing the manpower and time requirement. Reusable components come in many forms; it can be reusing a piece of code, a subsystem, or a whole software.
While you may be tempted to use many libraries/frameworks/platforms that seem to crop up on a regular basis and promise to bring great benefits, note that there are costs associated with reuse. Here are some:
An Application Programming Interface (API) specifies the interface through which other programs can interact with a software component. It is a contract between the component and its clients.
The GitHub API is a collection of web request formats that the GitHub server accepts and their corresponding responses. You can write a program that interacts with GitHub through that API.
When developing large systems, if you define the API of each component early, the development team can develop the components in parallel because the future behavior of the other components are now more predictable.
A library is a collection of modular code that is general and can be used by other programs.
Java classes you get with the JDK (such as
HashMap, etc.) are library classes that are provided in the default Java distribution.
Natty is a Java library that can be used for parsing strings that represent dates e.g.
The 31st of April in the year 2008
built-in modules you get with Python (such as
sys, etc.) are libraries that are provided in the default Python distribution. Classes such as
dict are built-in library classes that you get with Python.
Colorama is a Python library that can be used for colorizing text in a CLI.
These are the typical steps required to use a library:
The overall structure and execution flow of a specific category of software systems can be very similar. The similarity is an opportunity to reuse at a high scale.
IDEs for different programming languages are similar in how they support editing code, organizing project files, debugging, etc.
A software framework is a reusable implementation of a software (or part thereof) providing generic functionality that can be selectively customized to produce a specific application.
Eclipse is an IDE framework that can be used to create IDEs for different programming languages.
Some frameworks provide a complete implementation of a default behavior which makes them immediately usable.
Eclipse is a fully functional Java IDE out-of-the-box.
A framework facilitates the adaptation and customization of some desired functionality.
The Eclipse plugin system can be used to create an IDE for different programming languages while reusing most of the existing IDE features of Eclipse.
Some frameworks cover only a specific component or an aspect.
JavaFX is a framework for creating Java GUIs. Tkinter is a GUI framework for Python.
More examples of frameworks
Although both frameworks and libraries are reuse mechanisms, there are notable differences:
Libraries are meant to be used ‘as is’ while frameworks are meant to be customized/extended. e.g., writing plugins for Eclipse so that it can be used as an IDE for different languages (C++, PHP, etc.), adding modules and themes to Drupal, and adding test cases to JUnit.
Your code calls the library code while the framework code calls your code. Frameworks use a technique called inversion of control, aka the “Hollywood principle” (i.e. don’t call us, we’ll call you!). That is, you write code that will be called by the framework, e.g. writing test methods that will be called by the JUnit framework. In the case of libraries, your code calls libraries.
A platform provides a runtime environment for applications. A platform is often bundled with various libraries, tools, frameworks, and technologies in addition to a runtime environment but the defining characteristic of a software platform is the presence of a runtime environment.
Technically, an operating system can be called a platform. For example, Windows PC is a platform for desktop applications while iOS is a platform for mobile applications.
Two well-known examples of platforms are JavaEE and .NET, both of which sit above the operating systems layer, and are used to develop enterprise applications. Infrastructure services such as connection pooling, load balancing, remote code execution, transaction management, authentication, security, messaging etc. are done similarly in most enterprise applications. Both JavaEE and .NET provide these services to applications in a customizable way without developers having to implement them from scratch every time.