第9章ソフトウェア工学

As has been stated earlier, refactoring is the process of restructuring source code without changing its functionality. It is not specific to reuse, though refactoring can involve reuse. Typically, refactoring consists of making a series of elementary changes called micro-refactorings, such as:

• Rename an attribute, which changes the name of an attribute to a new one that better corresponds to its purpose.

• Rename a method, which changes the name of a method to a new one that better corresponds to its purpose.

• Extract a class, which moves a part of an existing class into a new class.

• Extract a method, which moves a fragment of code into a new method.

• Inline a method, which replaces a method call by its body. This is typically used only for very short methods.

• Move a method, which moves a method to a more appropriate class.

• Move a field, which moves a field to a more appropriate class.

• Remove dead code, which removes code that never executes.

• Replace a literal with a symbolic constant, which replaces a magic value with a named constant.

• Change method parameters, which adds or removes method parameters.

• Substitute an algorithm, which replaces one algorithm with another. This is typically done to improve performance of the software system.

You can apply these micro-refactorings manually, but it is more common to perform them in an IDE. Modern IDEs provide support for some refactoring, and you can often apply a selected refactoring by activating an appropriate menu item, as shown in Figure 9.26.

Returning to the concept of reuse, one of the benefits of refactoring is that functions, classes, and other chunks of code can be extracted from other parts of the code. These can then be reused by placing them in libraries, by incorporating them into a framework to be used by other developers, or by constructing an interface to access them.

When software engineers design and develop software for an organization, that software and all its code generally belong to the organization. This means the source code and functionality cannot be used by others without permission. This permission is typically controlled by a software license. The type of license can be determined by those who created the software or commissioned its creation. Two of the most common categories for defining software reuse are closed source and open source. Proprietary, or closed-source software, is a form of licensing that prohibits access to underlying source code. This type of software is typically developed for organizations or as software to be sold. It can be used to protect software that might contain proprietary information or intellectual property within the code. Free and open-source (FOSS), or open-source software, is a form of software licensing that provides access to the underlying code and generally allows the code to be reused and modified It is important to read the license terms of any software code used. It is also important to make sure that, if software is to be shared, it is clear as to what license will be applied to both the use of the software and its code. If a license is not provided with code, then the code is generally protected under copyright rules.

Free software (sometimes called libre software) is software distributed under the terms that provide users with the following four freedoms:

1. the freedom to run the software for any purpose

2. the freedom to study how the software works and modify it

3. the freedom to redistribute the software

4. the freedom to improve the software and release the improvements to the public

The freedom to study how the software works and modify it and the freedom to improve the software can hardly be fulfilled without source code, and so these freedoms more or less imply that source code of the software must be available.

Free here refers to liberty, not price (you may be required to pay for free software). Software that is distributed gratis is referred to as freeware, and it rarely comes with source code. Open-source software is software distributed under a license that grants users the right to use, study, modify, and distribute the software and its source code. It does not mean that software must be gratis, although in many cases it is the case. Today, it is common that open-source projects provide their source code via a public repository on the Internet that allows anybody to contribute.

The benefits of FOSS are as follows:

• Improved quality and reliability: Community involvement in open-source projects can lead to better quality and more reliable software due to a wider range of users and developers identifying and fixing bugs.

• Lower development costs: Open-source software can benefit from community contributions, reducing development costs for companies and organizations.

• Innovation: Openness and collaboration can accelerate innovation as developers can build upon existing open-source code.

Some projects that were developed as free and/or open-source software can be categorized as follows:

• Operating systems

◦ Linux: An open-source operating system, which is distributed in so-called distributions. The distributions are referred to by name such as Debian, Fedora, Ubuntu, RedHat, and SUSE, and they can be commercial (paid) or community-driven (gratis). The Linux kernel is licensed under GNU General Public License, version 2, which makes it a free and open-source software.

◦ Android: A free and open-source operating system developed by a consortium sponsored by Google. It is based on the Linux kernel and other open-source software, and it aims primarily to touchscreen mobile devices, such as smartphones and tablets. Android is the most common operating system (not only on mobile phones).

• Development tools

◦ NetBeans IDE: An open-source IDE that started as a student project with the goal of creating an IDE for the Java programming language. Now it belongs to Apache Software Foundation and also supports other programming languages, such as PHP, C, C++, and JavaScript.

◦ Eclipse IDE: An open-source integrated development environment that started at IBM and is now managed by the Eclipse Foundation.

◦ GNU Compiler Collection (GCC): A free and open-source compiler (or more precisely a suite of compilers) that supports various programming languages, hardware platforms, and operating systems. It is the standard compiler included in many Linux distributions.

• Web browsers

◦ Google Chrome: A no-cost web browser developed by Google. Although most source code of Google Chrome comes from free and open-source software, it is licensed as proprietary freeware. It is available on Windows, Linux, Android, macOS, and iOS.

◦ Mozilla Firefox: A free and open-source web browser developed by Mozilla Foundation. It is available on Windows, Linux, macOS, and Android.

• Programming languages

◦ OpenJDK: A free and open-source implementation of the Java Platform, Standard Edition. Many other distributions of the Java Platform, such as Amazon Corretto, are based on OpenJDK.

◦ C#: A modern cross-platform programming language initially developed by Microsoft. Both the C# language and the current (as of 2014) Microsoft C# compiler are open source.

◦ Python: A modern programming language is that is completely open source, freely usable and distributable, even for commercial use, making it extremely popular with businesses around the world.

• Application servers

◦ Payara Server: An open-source application server, with paid support options.

While some open-source software is entirely free, FOSS projects can have successful business models. It may seem that open-source software development does not bring any benefits to software publishing companies, but community involvement leads to better quality and higher reliability of the software and lower cost of development. Many software companies that moved to open-source development adequately modified their business model and instead of selling software, they charge the customer for providing additional services. For example, Payara Server is an open-source application server for Jakarta Enterprise Edition applications. The server is gratis, but companies that use Payara Server for mission-critical applications can pay for support, which allows them to consult a team of software engineers at any time. In addition, they receive monthly releases with bug fixes and security alerts. Many companies that embrace open-source development focus on providing value-added services, such as technical support, training, or custom development, around the core open-source product.

It is important for companies and developers to pay attention to the following:

• Software licensing considerations: Understanding software licenses is crucial for both software users and developers. While many people accept End User Licensing Agreements (EULAs) when installing software on their personal computers and devices, it is important that software engineers understand that these are legal agreements. As such, when using software to build solutions, it is important to understand what the licensing allows.

• Using open-source software: Software developers should be aware of the license terms associated with any FOSS they use to ensure compliance.

• Distributing software: Additionally, when distributing software, it is important to make sure that an included license defines how you or the organization that owns the software wants it used and protected. Choose a license that aligns with your project’s goals and how you want your software to be used and distributed.

FOSS is a powerful development model that fosters collaboration, innovation, and cost-effective software creation. While security considerations should also be factored in, open-source software plays a vital role in the tech industry.