Interface (computing)

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In computing, an interface is a shared boundary across which two or more separate components of a computer system exchange information. The exchange can be between software, computer hardware, peripheral devices, humans, and combinations of these. [1] Some computer hardware devices, such as a touchscreen, can both send and receive data through the interface, while others such as a mouse or microphone may only provide an interface to send data to a given system. [2]

Contents

Hardware interfaces

Hardware interfaces exist in many of the components, such as the various buses, storage devices, other I/O devices, etc. A hardware interface is described by the mechanical, electrical and logical signals at the interface and the protocol for sequencing them (sometimes called signaling). [3] A standard interface, such as SCSI, decouples the design and introduction of computing hardware, such as I/O devices, from the design and introduction of other components of a computing system, thereby allowing users and manufacturers great flexibility in the implementation of computing systems. [3] Hardware interfaces can be parallel with several electrical connections carrying parts of the data simultaneously, or serial where data are sent one bit at a time. [4]

Software interfaces

A software interface may refer to a wide range of different types of interface at different "levels": an operating system may interface with pieces of hardware. Applications or programs running on the operating system may need to interact via data streams, filters, and pipelines; [5] and in object oriented programs, objects within an application may need to interact via methods. [6]

In practice

A key principle of design is to prohibit access to all resources by default, allowing access only through well-defined entry points, i.e., interfaces. [7] Software interfaces provide access to computer resources (such as memory, CPU, storage, etc.) of the underlying computer system; direct access (i.e., not through well-designed interfaces) to such resources by software can have major ramifications—sometimes disastrous ones—for functionality and stability.[ citation needed ]

Interfaces between software components can provide constants, data types, types of procedures, exception specifications, and method signatures. Sometimes, public variables are also defined as part of an interface. [8]

The interface of a software module A is deliberately defined separately from the implementation of that module. The latter contains the actual code of the procedures and methods described in the interface, as well as other "private" variables, procedures, etc. Another software module B, for example the client to A, that interacts with A is forced to do so only through the published interface. One practical advantage of this arrangement is that replacing the implementation of A by another implementation of the same interface should not cause B to fail—how A internally meets the requirements of the interface is not relevant to B, which is only concerned with the specifications of the interface. (See also Liskov substitution principle.)[ citation needed ]

In object-oriented languages

In some object-oriented languages, especially those without full multiple inheritance, the term interface is used to define an abstract type that contains no data but defines behaviours as method signatures. A class having code and data for all the methods corresponding to that interface and declaring so is said to implement that interface. [9] Furthermore, even in single-inheritance-languages, one can implement multiple interfaces, and hence can be of different types at the same time. [10]

An interface is thus a type definition; anywhere an object can be exchanged (for example, in a function or method call) the type of the object to be exchanged can be defined in terms of one of its implemented interfaces or base-classes rather than specifying the specific class. This approach means that any class that implements that interface can be used.[ citation needed ] For example, a dummy implementation may be used to allow development to progress before the final implementation is available. In another case, a fake or mock implementation may be substituted during testing. Such stub implementations are replaced by real code later in the development process.

Usually a method defined in an interface contains no code and thus cannot itself be called; it must be implemented by non-abstract code to be run when it is invoked.[ citation needed ] An interface called " Stack " might define two methods: push() and pop(). It can be implemented in different ways, for example, FastStack and GenericStack—the first being fast, working with a data structure of fixed size, and the second using a data structure that can be resized, but at the cost of somewhat lower speed.

Though interfaces can contain many methods they may contain only one or even none at all. For example, the Java language defines the interface Readable that has the single read() method; various implementations are used for different purposes, including BufferedReader, FileReader, InputStreamReader, PipedReader, and StringReader. Marker interfaces like Serializable contain no methods at all and serve to provide run-time information to generic processing using Reflection. [11]

Programming to the interface

The use of interfaces allows for a programming style called programming to the interface. The idea behind this approach is to base programming logic on the interfaces of the objects used, rather than on internal implementation details. Programming to the interface reduces dependency on implementation specifics and makes code more reusable. [12]

Pushing this idea to the extreme, inversion of control leaves the context to inject the code with the specific implementations of the interface that will be used to perform the work.

User interfaces

A user interface is a point of interaction between a computer and humans; it includes any number of modalities of interaction (such as graphics, sound, position, movement, etc.) where data is transferred between the user and the computer system.

See also

Related Research Articles

Software Non-tangible executable component of a computer

Computer software, or simply software, is a collection of data or computer instructions that tell the computer how to work. This is in contrast to physical hardware, from which the system is built and actually performs the work. In computer science and software engineering, computer software is all information processed by computer systems, programs and data. Computer software includes computer programs, libraries and related non-executable data, such as online documentation or digital media. Computer hardware and software require each other and neither can be realistically used on its own.

In object-oriented programming, a class is an extensible program-code-template for creating objects, providing initial values for state and implementations of behavior. In many languages, the class name is used as the name for the class, the name for the default constructor of the class, and as the type of objects generated by instantiating the class; these distinct concepts are easily conflated.

In computing, serialization is the process of translating data structures or object state into a format that can be stored or transmitted and reconstructed later. When the resulting series of bits is reread according to the serialization format, it can be used to create a semantically identical clone of the original object. For many complex objects, such as those that make extensive use of references, this process is not straightforward. Serialization of object-oriented objects does not include any of their associated methods with which they were previously linked.

Java Platform, Standard Edition is a computing platform for development and deployment of portable code for desktop and server environments. Java SE was formerly known as Java 2 Platform, Standard Edition (J2SE).

The Common Object Request Broker Architecture (CORBA) is a standard defined by the Object Management Group (OMG) designed to facilitate the communication of systems that are deployed on diverse platforms. CORBA enables collaboration between systems on different operating systems, programming languages, and computing hardware. CORBA uses an object-oriented model although the systems that use the CORBA do not have to be object-oriented. CORBA is an example of the distributed object paradigm.

In software engineering and computer science, abstraction is:

In computer science, an object can be a variable, a data structure, a function, or a method, and as such, is a value in memory referenced by an identifier.

In computer science, separation of concerns (SoC) is a design principle for separating a computer program into distinct sections such that each section addresses a separate concern. A concern is a set of information that affects the code of a computer program. A concern can be as general as "the details of the hardware for an application", or as specific as "the name of which class to instantiate". A program that embodies SoC well is called a modular program. Modularity, and hence separation of concerns, is achieved by encapsulating information inside a section of code that has a well-defined interface. Encapsulation is a means of information hiding. Layered designs in information systems are another embodiment of separation of concerns.

ABAP is a high-level programming language created by the German software company SAP SE. It is extracted from the base computing languages Java, C, C++ and Python. It is currently positioned, alongside Java, as the language for programming the SAP NetWeaver Application Server, which is part of the SAP NetWeaver platform for building business applications.

In software engineering, inversion of control (IoC) is a programming principle. IoC inverts the flow of control as compared to traditional control flow. In IoC, custom-written portions of a computer program receive the flow of control from a generic framework. A software architecture with this design inverts control as compared to traditional procedural programming: in traditional programming, the custom code that expresses the purpose of the program calls into reusable libraries to take care of generic tasks, but with inversion of control, it is the framework that calls into the custom, or task-specific, code.

In object-oriented programming, inheritance is the mechanism of basing an object or class upon another object or class, retaining similar implementation. Also defined as deriving new classes from existing ones such as super class or base class and then forming them into a hierarchy of classes. In most class-based object-oriented languages, an object created through inheritance, a "child object", acquires all the properties and behaviors of the "parent object", with the exception of: constructors, destructor, overloaded operators and friend functions of the base class. Inheritance allows programmers to create classes that are built upon existing classes, to specify a new implementation while maintaining the same behaviors, to reuse code and to independently extend original software via public classes and interfaces. The relationships of objects or classes through inheritance give rise to a directed graph.

The Java programming language and Java software platform have been criticized for design choices in the language and platform, including the implementation of generics, forced object-oriented programming, the handling of unsigned numbers, the implementation of floating-point arithmetic, and a history of security vulnerabilities in the primary Java VM implementation, HotSpot. Additionally, software written in Java, especially its early versions, has been criticized for its performance compared to software written in other programming languages. Developers have also remarked that differences in various Java implementations must be taken into account when writing complex Java programs that must be used across these implementations.

In computing, object model has two related but distinct meanings:

  1. The properties of objects in general in a specific computer programming language, technology, notation or methodology that uses them. Examples are the object models of Java, the Component Object Model (COM), or Object-Modeling Technique (OMT). Such object models are usually defined using concepts such as class, generic function, message, inheritance, polymorphism, and encapsulation. There is an extensive literature on formalized object models as a subset of the formal semantics of programming languages.
  2. A collection of objects or classes through which a program can examine and manipulate some specific parts of its world. In other words, the object-oriented interface to some service or system. Such an interface is said to be the object model of the represented service or system. For example, the Document Object Model (DOM) is a collection of objects that represent a page in a web browser, used by script programs to examine and dynamically change the page. There is a Microsoft Excel object model for controlling Microsoft Excel from another program, and the ASCOM Telescope Driver is an object model for controlling an astronomical telescope.

In computer science, marshalling or marshaling is the process of transforming the memory representation of an object to a data format suitable for storage or transmission, and it is typically used when data must be moved between different parts of a computer program or from one program to another. Marshalling is similar to serialization and is used to communicate to remote objects with an object, in this case a serialized object. It simplifies complex communication, using composite objects in order to communicate instead of primitives. The inverse of marshalling is called unmarshalling.

In computer science, information hiding is the principle of segregation of the design decisions in a computer program that are most likely to change, thus protecting other parts of the program from extensive modification if the design decision is changed. The protection involves providing a stable interface which protects the remainder of the program from the implementation.

Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data, in the form of fields, and code, in the form of procedures. A feature of objects is an object's procedures that can access and often modify the data fields of the object with which they are associated. In OOP, computer programs are designed by making them out of objects that interact with one another. OOP languages are diverse, but the most popular ones are class-based, meaning that objects are instances of classes, which also determine their types.

An application programming interface (API) is a computing interface which defines interactions between multiple software intermediaries. It defines the kinds of calls or requests that can be made, how to make them, the data formats that should be used, the conventions to follow, etc. It can also provide extension mechanisms so that users can extend existing functionality in various ways and to varying degrees. An API can be entirely custom, specific to a component, or it can be designed based on an industry standard to ensure interoperability. Some APIs have to be documented, others are designed so that they can be "interrogated" to determine supported functionality. Since other components/systems rely only on the API, the system that provides the API can (ideally) change its internal details "behind" that API without affecting its users.

Telescript is an Agent-oriented programming language written by General Magic as part of the overall Magic Cap system. Telescript programs used a modified C-like syntax known as High Telescript and were compiled to a stack-based language called Low Telescript for execution. Low Telescript ran within virtual machine interpreters, or "Telescript engines", on host computers.

The composition filters model denotes a modular extension to the conventional object model. It provides a solution for a wide range of problems in the construction of large and complex applications. Most notably, one implementation of composition filters provides an abstraction layer for message-passing systems.

Most of the terms listed in Wikipedia glossaries are already defined and explained within Wikipedia itself. However, glossaries like this one are useful for looking up, comparing and reviewing large numbers of terms together. You can help enhance this page by adding new terms or writing definitions for existing ones.

References

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  2. IEEE 100 - The Authoritative Dictionary Of IEEE Standards Terms. NYC, NY, USA: IEEE Press. 2000. pp. 574–575. ISBN   9780738126012.
  3. 1 2 Blaauw, Gerritt A.; Brooks, Jr., Frederick P. (1997), "Chapter 8.6, Device Interfaces", Computer Architecture-Concepts and Evolution, Addison-Wesley, pp. 489–493, ISBN   0-201-10557-8 See also: Patterson, David A.; Hennessey, John L. (2005), "Chapter 8.5, Interfacing I/O Devices to the Processor, Memory and Operating System", Computer Organization and Design - The Hardware/Software Interface, Third Edition , Morgan Kaufmann, pp.  588–596, ISBN   1-55860-604-1
  4. Govindarajalu, B. (2008). "3.15 Peripheral Interfaces and Controllers - OG". IBM PC And Clones: Hardware, Troubleshooting And Maintenance. Tata McGraw-Hill Publishing Co. Ltd. pp. 142–144. ISBN   9780070483118 . Retrieved 15 June 2018.
  5. Buyya, R. (2013). Mastering Cloud Computing. Tata McGraw-Hill Education. p. 2.13. ISBN   9781259029950.
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  7. Bill Venners (2005-06-06). "Leading-Edge Java: Design Principles from Design Patterns: Program to an interface, not an implementation - A Conversation with Erich Gamma, Part III". http://www.artima.com/index.jsp: artima developer. Archived from the original on 2011-08-05. Retrieved 2011-08-03. Once you depend on interfaces only, you're decoupled from the implementation. That means the implementation can vary, and that is a healthy dependency relationship. For example, for testing purposes you can replace a heavy database implementation with a lighter-weight mock implementation. Fortunately, with today's refactoring support you no longer have to come up with an interface up front. You can distill an interface from a concrete class once you have the full insights into a problem. The intended interface is just one 'extract interface' refactoring away. ...
  8. Patterson, D.A.; Hennessy, J.L. Computer Organization and Design: The Hardware/Software Interface (3rd ed.). Elsevier. p. 656. ISBN   9780080502571.
  9. "What Is an Interface". The Java Tutorials. Oracle. Archived from the original on 2012-04-12. Retrieved 2012-05-01.
  10. "Interfaces". The Java Tutorials. Oracle. Archived from the original on 2012-05-26. Retrieved 2012-05-01.
  11. "Performance improvement techniques in Serialization". http://www.precisejava.com/: Precise Java. Archived from the original on 2011-08-24. Retrieved 2011-08-04. We will talk initially about Serializable interface. This is a marker interface and does not have any methods.
  12. Gamma; Helm; Johnson; Vlissides (1995). Design Patterns: Elements of Reusable Object-Oriented Software . Addison Wesley. pp.  17–18.