第7章高水準プログラミング言語

By the end of this section, you will be able to:

• Describe what HLLs are

• Summarize choosing appropriate HLLs

• Outline the history of HLLs

• Describe the implementation of HLLs

A high-level programming language is designed to be easy for humans to read, write, and understand. It abstracts away most of the complexities of the underlying hardware and machine code, allowing programmers to focus on solving problems and designing software without needing to manage the low-level details of the computer’s architecture.

High-level programming languages give humans the ability to direct computers to perform tasks and applications. There are many HLLs to choose from. Java is a popular choice for its ability to run on various operating systems (i.e., Windows, macOS, Linux) and mobile platforms (Android). This is called cross-platform compatibility. For development specifically targeting Windows systems, C# is another strong option. Additionally, to create the visual elements of a website, programmers can utilize HTML and CSS. HTML provides the structure and content of the web page, while CSS controls how web pages are styled and presented. Over time, many HLLs have evolved into a mature set of tools that are used to create modern applications (Figure 7.2).

There is a possibility that the widespread use of a variety of HLLs to develop networked and mobile applications at a global scale creates potential cybersecurity issues. Some HLLs are considered more secure than others. Read this article on the most secure programming languages (https://openstax.org/r/ 76ProgLanguages) for further information about the security—or lack thereof—of these languages.

Studying the fundamental concepts provided by various HLLs is necessary to choose them correctly, employ them effectively, and program efficiently. From a user point of view, examining HLL concepts helps the user get better at thinking and expressing algorithms. From an implementor’s point of view, understanding HLL concepts helps programmers abstract away from (virtual) machines and become better at specifying what they want the hardware to do without getting down into the bits. In the end, studying HLL concepts helps programmers make better use of whatever HLL they use.

One way to relate to abstraction is as a way of thinking and expressing algorithms to indicate what the programmer wants the hardware to do. For example, the following statement represents one form of abstraction in the Java programming language:

It tells the computer’s operating system at a high-level of abstraction to output a string of characters, which practically consists of moving the pixels that form characters one by one to a hardware device.

Implementing a high level of tasks would be impossible without abstraction. For example, you would not want to program an invoicing application in 1s and 0s (machine language); abstraction allows a programmer to build it in an English-like syntax.

Abstraction may be taken to much higher levels. It is one of three central principles (along with encapsulation and inheritance) in such object-oriented HLLs as C++, Java, C#, and Python. Various programming paradigms were introduced in Chapter 4 Linguistic Realization of Algorithms: Low-Level Programming Languages, particularly the mechanisms of object-oriented programming (OOP) and its standards, perspectives, or sets of ideas that may be used to describe the structure and methodologies of an HLL. Object-oriented HLLs help organize software design around data, or objects, rather than functions and logic, as we will discuss in Alternative Programming Models.

Studying and understanding HLL concepts allows us to make most efficient use of them by becoming familiar with various criteria that may be used to evaluate them, which helps us choose the most appropriate language for a project. Some of these criteria are listed in Table 7.1, which also shows how they are related to the characteristics of an HLL. These criteria are as follows:

• readability: measures how easily an HLL can be read and understood

• writability: measures how easily an HLL can be used to create and modify programs

• reliability: measures conformance to specifications

There are many other criteria including scalability, cost, flexibility, efficiency, portability, and maintainability. These can be used to identify which HLL is best suited for a given task.