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Software Engineering

SOLID (object-oriented design)

This article is about the SOLID principles of object-oriented programming. For the fundamental state of matter, see Solid. For other uses, see Solid (disambiguation).

SOLID
Principles of Object-Oriented Design
SSingle responsibility principle – SRP
OOpen–closed
LLiskov substitution principle – LSP
IInterface segregation principle – ISP
DDependency inversion – DI

“In object-oriented computer programmingSOLID is a mnemonic acronym for five design principles intended to make software designs more understandable, flexible, and maintainable. The principles are a subset of many principles promoted by American software engineer and instructor Robert C. Martin,[1][2][3] first introduced in his 2000 paper Design Principles and Design Patterns.[2][4]” (WP)

The SOLID concepts are:

The SOLID acronym was introduced later, around 2004, by Michael Feathers.[11]

“Although the SOLID principles apply to any object-oriented design, they can also form a core philosophy for methodologies such as agile development or adaptive software development.[3]” (WP)

See also

References

  1. ^ Robert C. Martin“Principles Of OOD”butunclebob.com. Retrieved 2014-07-17.. (Note the reference to “the first five principles”, although the acronym is not used in this article.) Dates back to at least 2003.
  2. a b Robert C. Martin. “Getting a SOLID start”objectmentor.com. Retrieved 2013-08-19.
  3. a b Sandi Metz (May 2009). “SOLID Object-Oriented Design”. Retrieved 2019-08-13. Talk given at the 2009 Gotham Ruby Conference.
  4. a b c Martin, Robert C. (2000). “Design Principles and Design Patterns” (PDF). Archived from the original (PDF) on 2015-09-06.
  5. ^ “Single Responsibility Principle” (PDF). objectmentor.com. Archived from the original (PDF) on 2 February 2015.
  6. ^ Martin, Robert C. (2003). Agile Software Development, Principles, Patterns, and Practices. Prentice Hall. p. 95. ISBN 978-0135974445.
  7. ^ “Open/Closed Principle” (PDF). objectmentor.com. Archived from the original (PDF) on 5 September 2015.
  8. ^ “Liskov Substitution Principle” (PDF). objectmentor.com. Archived from the original (PDF) on 5 September 2015.
  9. ^ “Interface Segregation Principle” (PDF). objectmentor.com. 1996. Archived from the original (PDF) on 5 September 2015.
  10. ^ “Dependency Inversion Principle” (PDF). objectmentor.com. Archived from the original (PDF) on 5 September 2015.
  11. ^ Martin, Robert (2018). Clean Architecture: A Craftsman’s Guide to Software Structure and Design. p. 58. ISBN 9780134494166.

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Bibliography JavaScript Software Engineering

The Principles of Object-Oriented JavaScript

See also: JavaScript Bibliography and Bibliography of JavaScript Libraries and Web Frameworks

The Principles of Object-Oriented JavaScript, 1st Edition, by Nicholas C. Zakas, 2014, B00I87B1H8 (POOJS)

About This Book:

If you’ve used a more traditional object-oriented language, such as C++ or Java, JavaScript probably doesn’t seem object-oriented at all. It has no concept of classes, and you don’t even need to define any objects in order to write code. But don’t be fooled—JavaScript is an incredibly powerful and expressive object-oriented language that puts many design decisions right into your hands.

In The Principles of Object-Oriented JavaScript, Nicholas C. Zakas thoroughly explores JavaScript’s object-oriented nature, revealing the language’s unique implementation of inheritance and other key characteristics. You’ll learn:
–The difference between primitive and reference values
–What makes JavaScript functions so unique
–The various ways to create objects
–How to define your own constructors
–How to work with and understand prototypes
–Inheritance patterns for types and objects

The Principles of Object-Oriented JavaScript will leave even experienced developers with a deeper understanding of JavaScript. Unlock the secrets behind how objects work in JavaScript so you can write clearer, more flexible, and more efficient code.

Review:

“Completely changes my understanding of JavaScript…The best part of the book is its concise nature and the way it explains concepts.” — Javin Paul, Java Revisited

About the Author:

Nicholas C. Zakas is a software engineer at Box and is known for writing on and speaking about the latest in JavaScript best practices. He honed his experience during his five years at Yahoo!, where he was principal front­end engineer for the Yahoo! home page. He is the author of several books, including Maintainable JavaScript (O’Reilly Media, 2012), Understanding ECMAScript 6: The Definitive Guide for JavaScript Developers (2016), and Professional JavaScript for Web Developers (Wrox, 2012).

Book Details:

  • ASIN: B00I87B1H8
  • ISBN-10: 9781593275402
  • ISBN-13: 978-1593275402
  • Publisher: No Starch Press; 1st edition (February 14, 2014)
  • Publication date: February 14, 2014
  • Print length: 147 pages

Table of Contents:

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History Software Engineering

D Programming Language Invented – 1999 AD

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Development of the D programming language started in December 1999. D is a higher level language compared to C++.

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History Software Engineering

OCaml Programming Language Invented – 1996 AD

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Introduced in 1996, OCaml is an object-oriented version of the Caml programming language.

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Cloud History JavaScript Software Engineering

JavaScript Programming Language Invented by Brendan Eich – 1995 AD

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See also: You Don’t Know JS Yet (YDKJSY) JavaScript Book Series by Kyle Simpson, JavaScript Bibliography and Bibliography of JavaScript Libraries and Web Frameworks

Originally named LiveScript when released in November 1995, JavaScript was developed by Brendan Eich and renamed as such in December 1995.

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History Software Engineering Swift

Objective-C Programming Language Invented by Brad Cox and Tom Love – 1988 AD

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Developed in the mid-1980s by Brad Cox and Tom Love, the Objective-C programming language was officially licensed by NeXT in 1988.

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History Software Engineering

C++ Programming Language Invented by Bjarne Stroustrup – 1979 AD

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Development of the C++ programming language was started in 1979 by Bjarne Stroustrup. Originally called “C with classes,” C++ is one of the most widely-used programming languages.

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History Software Engineering

Smalltalk Programming Language Invented by Alan Kay of Xerox PARC – Second ever Object-Oriented – First IDE – 1972 AD

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Smalltalk was the second ever object-oriented programming language and the first true IDE, developed by Alan Kay and others at Xerox PARC in 1972.

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See also Xerox Alto from Xerox Palo Alto Research Center (PARC) – 1973 AD

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History Software Engineering

Simula Programming Language Invented – First ever Object-Oriented – 1965 AD

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Simula is considered the first ever object-oriented programming language, developed around 1965 by Ole-Johan Dahl and Kristen Nygaard.

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History Python Software Engineering

Python Programming Language Invented by Guido van Rossum – 1991 AD

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Development of Python was started in 1989 by Guido van Rossum and released to the public in 1991.

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History Java Software Engineering

Java Programming Language – Invented by James Gosling of Sun Microsystems – 1995 AD – Java language

See also Java Programming Language, Java Glossary, Java Bibliography, Java Reference materials, Timeline of the History of Computers

It is not to be confused with Javanese language (LOL Haha). Not to be confused with JavaScript.

May 23, 1995 – Sun Microsystems first announces Java at the SunWorld conference.

Java programming language logo.svg
ParadigmMulti-paradigmgenericobject-oriented (class-based), imperativereflective
Designed byJames Gosling
DeveloperOracle Corporation
First appearedMay 23, 1995; 25 years ago[1]
Stable releaseJava SE 16 / March 16, 2021; 12 days ago
Typing disciplineStatic, strong, safenominativemanifest
Filename extensions.java, .class.jar
Websiteoracle.com/java/
Influenced by
CLU,[2] Simula67,[2] LISP,[2] SmallTalk,[2] Ada 83C++,[3] C#,[4] Eiffel,[5] Mesa,[6] Modula-3,[7] Oberon,[8] Objective-C,[9] UCSD Pascal,[10][11] Object Pascal[12]
Influenced
Ada 2005BeanShellC#Chapel,[13] ClojureECMAScriptFantomGambas,[14] GroovyHack,[15] HaxeJ#KotlinPHPPythonScalaSeed7ValaJavaScript
 Java Programming at Wikibooks

Java is a class-basedobject-oriented programming language that is designed to have as few implementation dependencies as possible. It is a general-purpose programming language intended to let application developers write once, run anywhere (WORA),[16] meaning that compiled Java code can run on all platforms that support Java without the need for recompilation.[17] Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of the underlying computer architecture. The syntax of Java is similar to C and C++, but has fewer low-level facilities than either of them. The Java runtime provides dynamic capabilities (such as reflection and runtime code modification) that are typically not available in traditional compiled languages. As of 2019, Java was one of the most popular programming languages in use according to GitHub,[18][19] particularly for client-server web applications, with a reported 9 million developers.[20]” (WP)

Java was originally developed by James Gosling at Sun Microsystems (which has since been acquired by Oracle) and released in 1995 as a core component of Sun Microsystems’ Java platform. The original and reference implementation Java compilers, virtual machines, and class libraries were originally released by Sun under proprietary licenses. As of May 2007, in compliance with the specifications of the Java Community Process, Sun had relicensed most of its Java technologies under the GNU General Public License. Oracle offers its own HotSpot Java Virtual Machine, however the official reference implementation is the OpenJDK JVM which is free open source software and used by most developers and is the default JVM for almost all Linux distributions.

As of March 2021, the latest version is Java 16, with Java 11, a currently supported long-term support (LTS) version, released on September 25, 2018. Oracle released the last zero-cost public update for the legacy version Java 8 LTS in January 2019 for commercial use, although it will otherwise still support Java 8 with public updates for personal use indefinitely. Other vendors have begun to offer zero-cost builds of OpenJDK 8 and 11 that are still receiving security and other upgrades.

Oracle (and others) highly recommend uninstalling outdated versions of Java because of serious risks due to unresolved security issues.[21] Since Java 9, 10, 12, 13, 14, and 15 are no longer supported, Oracle advises its users to immediately transition to the latest version (currently Java 16) or an LTS release.

History

See also: Java (software platform) § History Duke, the Java mascot

James Gosling, the creator of Java, in 2008

The TIOBE programming language popularity index graph from 2002 to 2018. Java was steadily on the top from mid-2015 to early 2020.

James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991.[22] Java was originally designed for interactive television, but it was too advanced for the digital cable television industry at the time.[23] The language was initially called Oak after an oak tree that stood outside Gosling’s office. Later the project went by the name Green and was finally renamed Java, from Java coffee, a type of coffee from Indonesia.[24] Gosling designed Java with a C/C++-style syntax that system and application programmers would find familiar.[25]

Sun Microsystems released the first public implementation as Java 1.0 in 1996.[26] It promised Write Once, Run Anywhere (WORA) functionality, providing no-cost run-times on popular platforms. Fairly secure and featuring configurable security, it allowed network- and file-access restrictions. Major web browsers soon incorporated the ability to run Java applets within web pages, and Java quickly became popular. The Java 1.0 compiler was re-written in Java by Arthur van Hoff to comply strictly with the Java 1.0 language specification.[27] With the advent of Java 2 (released initially as J2SE 1.2 in December 1998 – 1999), new versions had multiple configurations built for different types of platforms. J2EE included technologies and APIs for enterprise applications typically run in server environments, while J2ME featured APIs optimized for mobile applications. The desktop version was renamed J2SE. In 2006, for marketing purposes, Sun renamed new J2 versions as Java EEJava ME, and Java SE, respectively.

In 1997, Sun Microsystems approached the ISO/IEC JTC 1 standards body and later the Ecma International to formalize Java, but it soon withdrew from the process.[28][29][30] Java remains a de facto standard, controlled through the Java Community Process.[31] At one time, Sun made most of its Java implementations available without charge, despite their proprietary software status. Sun generated revenue from Java through the selling of licenses for specialized products such as the Java Enterprise System.

On November 13, 2006, Sun released much of its Java virtual machine (JVM) as free and open-source software (FOSS), under the terms of the GNU General Public License (GPL). On May 8, 2007, Sun finished the process, making all of its JVM’s core code available under free software/open-source distribution terms, aside from a small portion of code to which Sun did not hold the copyright.[32]

Sun’s vice-president Rich Green said that Sun’s ideal role with regard to Java was as an evangelist.[33] Following Oracle Corporation‘s acquisition of Sun Microsystems in 2009–10, Oracle has described itself as the steward of Java technology with a relentless commitment to fostering a community of participation and transparency.[34] This did not prevent Oracle from filing a lawsuit against Google shortly after that for using Java inside the Android SDK (see the Android section).

On April 2, 2010, James Gosling resigned from Oracle.[35]

In January 2016, Oracle announced that Java run-time environments based on JDK 9 will discontinue the browser plugin.[36]

Java software runs on everything from laptops to data centersgame consoles to scientific supercomputers.[37]

Java’s Origins

“The seeds of Java were planted in 1990 by Sun Microsystems patriarch and chief researcher Bill Joy. At the time, Sun was competing in a relatively small workstation market, while Microsoft was beginning its domination of the more mainstream, Intel-based PC world. When Sun missed the boat on the PC revolution, Joy retreated to Aspen, Colorado, to work on advanced research. He was committed to the idea of accomplishing complex tasks with simple software and founded the aptly named Sun Aspen Smallworks.” (B086L2NYWR)

“Of the original members of the small team of programmers assembled in Aspen, James Gosling will be remembered as the father of Java. Gosling first made a name for himself in the early 80s as the author of Gosling Emacs, the first version of the popular Emacs editor that was written in C and ran under Unix. Gosling Emacs became popular but was soon eclipsed by a free version, GNU Emacs, written by Emacs’s original designer. By that time, Gosling had moved on to design Sun’s NeWS, which briefly contended with the X Window System for control of the Unix GUI desktop in 1987. Although some people would argue that NeWS was superior to X, NeWS lost because Sun kept it proprietary and didn’t publish source code, while the primary developers of X formed the X Consortium and took the opposite approach.” (B086L2NYWR)

“Designing NeWS taught Gosling the power of integrating an expressive language with a network-aware windowing GUI. It also taught Sun that the internet programming community will ultimately refuse to accept proprietary standards, no matter how good they may be. The seeds of Java’s licensing scheme and open (if not quite “open source”) code were sown by NeWS’s failure. Gosling brought what he had learned to Bill Joy’s nascent Aspen project. In 1992, work on the project led to the founding of the Sun subsidiary FirstPerson, Inc. Its mission was to lead Sun into the world of consumer electronics.” (B086L2NYWR)

“The FirstPerson team worked on developing software for information appliances, such as cellular phones and personal digital assistants (PDAs). The goal was to enable the transfer of information and real-time applications over cheap infrared and traditional packet-based networks. Memory and bandwidth limitations dictated small, efficient code. The nature of the applications also demanded they be safe and robust. Gosling and his teammates began programming in C++, but they soon found themselves confounded by a language that was too complex, unwieldy, and insecure for the task. They decided to start from scratch, and Gosling began working on something he dubbed “C++ minus minus.””(B086L2NYWR)

“With the foundering of the Apple Newton (Apple’s earliest handheld computer), it became apparent that the PDA’s ship had not yet come in, so Sun shifted FirstPerson’s efforts to interactive TV (ITV). The programming language of choice for ITV set-top boxes was to be the near ancestor of Java, a language called Oak. Even with its elegance and ability to provide safe interactivity, Oak could not salvage the lost cause of ITV at that time. Customers didn’t want it, and Sun soon abandoned the concept.” (B086L2NYWR)

“At that time, Joy and Gosling got together to decide on a new strategy for their innovative language. It was 1993, and the explosion of interest in the web presented a new opportunity. Oak was small, safe, architecture-independent, and object-oriented. As it happens, these are also some of the requirements for a universal, internet-savvy programming language. Sun quickly changed focus, and, with a little retooling, Oak became Java.” (B086L2NYWR)

Java Growing Up

“It wouldn’t be an overstatement to say that Java (and its developer-focused bundle, the Java Development Kit, or JDK) caught on like wildfire. Even before its first official release when Java was still a nonproduct, nearly every major industry player had jumped on the Java bandwagon. Java licensees included Microsoft, Intel, IBM, and virtually all major hardware and software vendors. However, even with all this support, Java took a lot of knocks and experienced some growing pains during its first few years.” (B086L2NYWR)

“A series of breach of contract and antitrust lawsuits between Sun and Microsoft over the distribution of Java and its use in Internet Explorer hampered its deployment on the world’s most common desktop operating system — Windows. Microsoft’s involvement with Java also become one focus of a larger federal lawsuit over serious anticompetitive practices at the company, with court testimony revealing concerted efforts by the software giant to undermine Java by introducing incompatibilities in its version of the language. Meanwhile, Microsoft introduced its own Java-derived language called C# (C-sharp) as part of its .NET initiative and dropped Java from inclusion in Windows. C# has gone on to become a very good language in its own right, enjoying more innovation in recent years than has Java.” (B086L2NYWR)

“But Java continues to spread on a wide variety of platforms. As we begin looking at the Java architecture, you’ll see that much of what is exciting about Java comes from the self-contained, virtual machine environment in which Java applications run. Java was carefully designed so that this supporting architecture can be implemented either in software, for existing computer platforms, or in customized hardware. Hardware implementations of Java are used in some smart cards and other embedded systems. You can even buy “wearable” devices, such as rings and dog tags, that have Java interpreters embedded in them. Software implementations of Java are available for all modern computer platforms down to portable computing devices. Today, an offshoot of the Java platform is the basis for Google’s Android operating system that powers billions of phones and other mobile devices.” (B086L2NYWR)

“In 2010, Oracle corporation bought Sun Microsystems and became the steward of the Java language. In a somewhat rocky start to its tenure, Oracle sued Google over its use of the Java language in Android and lost. In July of 2011, Oracle released Java SE 7, a significant Java release including a new I/O package in 2017. Java 9 introduced modules to address some long-standing issues with the classpath and the growing size of the JDK itself. Java 9 also kicked off a rapid update process leading to Java 11 being the current version with long-term support. (More on these and other versions in “A Java Road Map”.) Oracle continues to lead Java development; however, they have also bifurcated the Java world by moving the main Java deployment environment to a costly commercial license and offering a free subsidiary OpenJDK option that retains the accessibility many developers love and expect.” (B086L2NYWR)

Principles

There were five primary goals in the creation of the Java language:[17]

  1. It must be simple, object-oriented, and familiar.
  2. It must be robust and secure.
  3. It must be architecture-neutral and portable.
  4. It must execute with high performance.
  5. It must be interpretedthreaded, and dynamic.

Versions

Main article: Java version history

As of September 2020, Java 8 and 11 are supported as Long Term Support (LTS) versions, and one later non-LTS version is supported.[38] Major release versions of Java, along with their release dates:

VersionDate
JDK Beta1995
JDK1.0January 23, 1996[39]
JDK 1.1February 19, 1997
J2SE 1.2December 8, 1998
J2SE 1.3May 8, 2000
J2SE 1.4February 6, 2002
J2SE 5.0September 30, 2004
Java SE 6December 11, 2006
Java SE 7July 28, 2011
Java SE 8March 18, 2014
Java SE 9September 21, 2017
Java SE 10March 20, 2018
Java SE 11September 25, 2018[40]
Java SE 12March 19, 2019
Java SE 13September 17, 2019
Java SE 14March 17, 2020
Java SE 15September 15, 2020[41]
Java SE 16March 16, 2021

Editions

See also: Free Java implementations § Class library

Java platform editions
Java CardJava ME (Micro)

Java SE (Standard)

Jakarta EE (Enterprise)

JavaFX (bundled in JRE from 8 to 10 but separately for JavaFX 1.x, 2.x and again since 11)

PersonalJava (Discontinued)

Sun has defined and supports four editions of Java targeting different application environments and segmented many of its APIs so that they belong to one of the platforms. The platforms are:

The classes in the Java APIs are organized into separate groups called packages. Each package contains a set of related interfaces, classes, subpackages and exceptions.

Sun also provided an edition called Personal Java that has been superseded by later, standards-based Java ME configuration-profile pairings.

Execution system

Java JVM and bytecode

Main articles: Java (software platform) and Java virtual machine

One design goal of Java is portability, which means that programs written for the Java platform must run similarly on any combination of hardware and operating system with adequate run time support. This is achieved by compiling the Java language code to an intermediate representation called Java bytecode, instead of directly to architecture-specific machine code. Java bytecode instructions are analogous to machine code, but they are intended to be executed by a virtual machine (VM) written specifically for the host hardware. End users commonly use a Java Runtime Environment (JRE) installed on their machine for standalone Java applications, or in a web browser for Java applets.

Standard libraries provide a generic way to access host-specific features such as graphics, threading, and networking.

The use of universal bytecode makes porting simple. However, the overhead of interpreting bytecode into machine instructions made interpreted programs almost always run more slowly than native executablesJust-in-time (JIT) compilers that compile byte-codes to machine code during runtime were introduced from an early stage. Java itself is platform-independent and is adapted to the particular platform it is to run on by a Java virtual machine (JVM) for it, which translates the Java bytecode into the platform’s machine language.[46]

Performance

Main article: Java performance

Programs written in Java have a reputation for being slower and requiring more memory than those written in C++ .[47][48] However, Java programs’ execution speed improved significantly with the introduction of just-in-time compilation in 1997/1998 for Java 1.1,[49] the addition of language features supporting better code analysis (such as inner classes, the StringBuilder class, optional assertions, etc.), and optimizations in the Java virtual machine, such as HotSpot becoming Sun’s default JVM in 2000. With Java 1.5, the performance was improved with the addition of the java.util.concurrent package, including lock free implementations of the ConcurrentMaps and other multi-core collections, and it was improved further with Java 1.6.

Non-JVM

Some platforms offer direct hardware support for Java; there are micro controllers that can run Java bytecode in hardware instead of a software Java virtual machine,[50] and some ARM-based processors could have hardware support for executing Java bytecode through their Jazelle option, though support has mostly been dropped in current implementations of ARM.

Automatic memory management

Java uses an automatic garbage collector to manage memory in the object lifecycle. The programmer determines when objects are created, and the Java runtime is responsible for recovering the memory once objects are no longer in use. Once no references to an object remain, the unreachable memory becomes eligible to be freed automatically by the garbage collector. Something similar to a memory leak may still occur if a programmer’s code holds a reference to an object that is no longer needed, typically when objects that are no longer needed are stored in containers that are still in use. If methods for a non-existent object are called, a null pointer exception is thrown.[51][52]

One of the ideas behind Java’s automatic memory management model is that programmers can be spared the burden of having to perform manual memory management. In some languages, memory for the creation of objects is implicitly allocated on the stack or explicitly allocated and deallocated from the heap. In the latter case, the responsibility of managing memory resides with the programmer. If the program does not deallocate an object, a memory leak occurs. If the program attempts to access or deallocate memory that has already been deallocated, the result is undefined and difficult to predict, and the program is likely to become unstable or crash. This can be partially remedied by the use of smart pointers, but these add overhead and complexity. Note that garbage collection does not prevent logical memory leaks, i.e. those where the memory is still referenced but never used.

Garbage collection may happen at any time. Ideally, it will occur when a program is idle. It is guaranteed to be triggered if there is insufficient free memory on the heap to allocate a new object; this can cause a program to stall momentarily. Explicit memory management is not possible in Java.

Java does not support C/C++ style pointer arithmetic, where object addresses can be arithmetically manipulated (e.g. by adding or subtracting an offset). This allows the garbage collector to relocate referenced objects and ensures type safety and security.

As in C++ and some other object-oriented languages, variables of Java’s primitive data types are either stored directly in fields (for objects) or on the stack (for methods) rather than on the heap, as is commonly true for non-primitive data types (but see escape analysis). This was a conscious decision by Java’s designers for performance reasons.

Java contains multiple types of garbage collectors. Since Java 9, HotSpot uses the Garbage First Garbage Collector (G1GC) as the default.[53] However, there are also several other garbage collectors that can be used to manage the heap. For most applications in Java, G1GC is sufficient. Previously, the Parallel Garbage Collector was used in Java 8.

Having solved the memory management problem does not relieve the programmer of the burden of handling properly other kinds of resources, like network or database connections, file handles, etc., especially in the presence of exceptions.

Syntax

Main article: Java syntax

Dependency graph of the Java Core classes (created with jdeps and Gephi)

The syntax of Java is largely influenced by C++ and C. Unlike C++, which combines the syntax for structured, generic, and object-oriented programming, Java was built almost exclusively as an object-oriented language.[17] All code is written inside classes, and every data item is an object, with the exception of the primitive data types, (i.e. integers, floating-point numbers, boolean values, and characters), which are not objects for performance reasons. Java reuses some popular aspects of C++ (such as the printf method).

Unlike C++, Java does not support operator overloading[54] or multiple inheritance for classes, though multiple inheritance is supported for interfaces.[55]

Java uses comments similar to those of C++. There are three different styles of comments: a single line style marked with two slashes (//), a multiple line style opened with /* and closed with */, and the Javadoc commenting style opened with /** and closed with */. The Javadoc style of commenting allows the user to run the Javadoc executable to create documentation for the program and can be read by some integrated development environments (IDEs) such as Eclipse to allow developers to access documentation within the IDE.

Hello world example

The traditional Hello world program can be written in Java as:[56]

public class HelloWorldApp {
    public static void main(String[] args) {
        System.out.println("Hello World!"); // Prints the string to the console.
    }
}

All source files must be named after the public class they contain, appending the suffix .java, for example, HelloWorldApp.java. It must first be compiled into bytecode, using a Java compiler, producing a file with the .class suffix (HelloWorldApp.class, in this case). Only then can it be executed or launched. The Java source file may only contain one public class, but it can contain multiple classes with a non-public access modifier and any number of public inner classes. When the source file contains multiple classes, it is necessary to make one class (introduced by the class keyword) public (preceded by the public keyword) and name the source file with that public class name.

A class that is not declared public may be stored in any .java file. The compiler will generate a class file for each class defined in the source file. The name of the class file is the name of the class, with .class appended. For class file generation, anonymous classes are treated as if their name were the concatenation of the name of their enclosing class, a $, and an integer.

The keyword public denotes that a method can be called from code in other classes, or that a class may be used by classes outside the class hierarchy. The class hierarchy is related to the name of the directory in which the .java file is located. This is called an access level modifier. Other access level modifiers include the keywords private (a method that can only be accessed in the same class) and protected (which allows code from the same package to access). If a piece of code attempts to access private methods or protected methods, the JVM will throw a SecurityException

The keyword static[18] in front of a method indicates a static method, which is associated only with the class and not with any specific instance of that class. Only static methods can be invoked without a reference to an object. Static methods cannot access any class members that are not also static. Methods that are not designated static are instance methods and require a specific instance of a class to operate.

The keyword void indicates that the main method does not return any value to the caller. If a Java program is to exit with an error code, it must call System.exit() explicitly.

The method name main is not a keyword in the Java language. It is simply the name of the method the Java launcher calls to pass control to the program. Java classes that run in managed environments such as applets and Enterprise JavaBeans do not use or need a main() method. A Java program may contain multiple classes that have main methods, which means that the VM needs to be explicitly told which class to launch from.

The main method must accept an array of String objects. By convention, it is referenced as args although any other legal identifier name can be used. Since Java 5, the main method can also use variable arguments, in the form of public static void main(String... args), allowing the main method to be invoked with an arbitrary number of String arguments. The effect of this alternate declaration is semantically identical (to the args parameter which is still an array of String objects), but it allows an alternative syntax for creating and passing the array.

The Java launcher launches Java by loading a given class (specified on the command line or as an attribute in a JAR) and starting its public static void main(String[]) method. Stand-alone programs must declare this method explicitly. The String[] args parameter is an array of String objects containing any arguments passed to the class. The parameters to main are often passed by means of a command line.

Printing is part of a Java standard library: The System class defines a public static field called out. The out object is an instance of the PrintStream class and provides many methods for printing data to standard out, including println(String) which also appends a new line to the passed string.

The string "Hello World!" is automatically converted to a String object by the compiler.

Example with methods

// This is an example of a single line comment using two slashes

/*
 * This is an example of a multiple line comment using the slash and asterisk.
 * This type of comment can be used to hold a lot of information or deactivate
 * code, but it is very important to remember to close the comment.
 */

package fibsandlies;

import java.util.Map;
import java.util.HashMap;

/**
 * This is an example of a Javadoc comment; Javadoc can compile documentation
 * from this text. Javadoc comments must immediately precede the class, method,
 * or field being documented.
 * @author Wikipedia Volunteers
 */
public class FibCalculator extends Fibonacci implements Calculator {
    private static Map<Integer, Integer> memoized = new HashMap<>();

    /*
     * The main method written as follows is used by the JVM as a starting point
     * for the program.
     */
    public static void main(String[] args) {
        memoized.put(1, 1);
        memoized.put(2, 1);
        System.out.println(fibonacci(12)); // Get the 12th Fibonacci number and print to console
    }

    /**
     * An example of a method written in Java, wrapped in a class.
     * Given a non-negative number FIBINDEX, returns
     * the Nth Fibonacci number, where N equals FIBINDEX.
     * 
     * @param fibIndex The index of the Fibonacci number
     * @return the Fibonacci number
     */
    public static int fibonacci(int fibIndex) {
        if (memoized.containsKey(fibIndex)) return memoized.get(fibIndex);
        else {
            int answer = fibonacci(fibIndex - 1) + fibonacci(fibIndex - 2);
            memoized.put(fibIndex, answer);
            return answer;
        }
    }
}

Special classes

Applet

Main article: Java applet

Java applets were programs that were embedded in other applications, typically in a Web page displayed in a web browser. The Java applet API is now deprecated since Java 8 in 2017.[57][58]

Servlet

Main article: Java servlet

Java servlet technology provides Web developers with a simple, consistent mechanism for extending the functionality of a Web server and for accessing existing business systems. Servlets are server-side Java EE components that generate responses to requests from clients. Most of the time, this means generating HTML pages in response to HTTP requests, although there are a number of other standard servlet classes available, for example for WebSocket communication.

The Java servlet API has to some extent been superseded (but still used under the hood) by two standard Java technologies for web services:

Typical implementations of these APIs on Application Servers or Servlet Containers use a standard servlet for handling all interactions with the HTTP requests and responses that delegate to the web service methods for the actual business logic.

JavaServer Pages

Main article: JavaServer Pages

JavaServer Pages (JSP) are server-side Java EE components that generate responses, typically HTML pages, to HTTP requests from clients. JSPs embed Java code in an HTML page by using the special delimiters <% and %>. A JSP is compiled to a Java servlet, a Java application in its own right, the first time it is accessed. After that, the generated servlet creates the response.[59]

Swing application

Main article: Swing (Java)

Swing is a graphical user interface library for the Java SE platform. It is possible to specify a different look and feel through the pluggable look and feel system of Swing. Clones of WindowsGTK+, and Motif are supplied by Sun. Apple also provides an Aqua look and feel for macOS. Where prior implementations of these looks and feels may have been considered lacking, Swing in Java SE 6 addresses this problem by using more native GUI widget drawing routines of the underlying platforms.[60]

JavaFX application

Main article: JavaFX

JavaFX is a software platform for creating and delivering desktop applications, as well as rich web applications that can run across a wide variety of devices. JavaFX is intended to replace Swing as the standard GUI library for Java SE, but since JDK 11 JavaFX has not been in the core JDK and instead in a separate module.[61] JavaFX has support for desktop computers and web browsers on Microsoft WindowsLinux, and macOS. JavaFX does not have support for native OS look and feels.[62]

Generics

Main article: Generics in Java

In 2004, generics were added to the Java language, as part of J2SE 5.0. Prior to the introduction of generics, each variable declaration had to be of a specific type. For container classes, for example, this is a problem because there is no easy way to create a container that accepts only specific types of objects. Either the container operates on all subtypes of a class or interface, usually Object, or a different container class has to be created for each contained class. Generics allow compile-time type checking without having to create many container classes, each containing almost identical code. In addition to enabling more efficient code, certain runtime exceptions are prevented from occurring, by issuing compile-time errors. If Java prevented all runtime type errors (ClassCastExceptions) from occurring, it would be type safe.

In 2016, the type system of Java was proven unsound.[63]

Criticism

Main article: Criticism of Java

Criticisms directed at Java include the implementation of generics,[64] speed,[65] the handling of unsigned numbers,[66] the implementation of floating-point arithmetic,[67] and a history of security vulnerabilities in the primary Java VM implementation HotSpot.[68]

Class libraries

Main article: Java Class Library

The Java Class Library is the standard library, developed to support application development in Java. It is controlled by Oracle in cooperation with others through the Java Community Process program.[69] Companies or individuals participating in this process can influence the design and development of the APIs. This process has been a subject of controversy during the 2010s.[70] The class library contains features such as:

Documentation

Main article: Javadoc

Javadoc is a comprehensive documentation system, created by Sun Microsystems. It provides developers with an organized system for documenting their code. Javadoc comments have an extra asterisk at the beginning, i.e. the delimiters are /** and */, whereas the normal multi-line comments in Java are set off with the delimiters /* and */, and single-line comments start off the line with //.[74]

Implementations

See also: Free Java implementations

Oracle Corporation is the current owner of the official implementation of the Java SE platform, following their acquisition of Sun Microsystems on January 27, 2010. This implementation is based on the original implementation of Java by Sun. The Oracle implementation is available for Microsoft Windows (still works for XP, while only later versions are currently officially supported), macOSLinux, and Solaris. Because Java lacks any formal standardization recognized by Ecma International, ISO/IEC, ANSI, or other third-party standards organizations, the Oracle implementation is the de facto standard.

The Oracle implementation is packaged into two different distributions: The Java Runtime Environment (JRE) which contains the parts of the Java SE platform required to run Java programs and is intended for end users, and the Java Development Kit (JDK), which is intended for software developers and includes development tools such as the Java compilerJavadocJar, and a debugger. Oracle has also released GraalVM, a high performance Java dynamic compiler and interpreter.

OpenJDK is another notable Java SE implementation that is licensed under the GNU GPL. The implementation started when Sun began releasing the Java source code under the GPL. As of Java SE 7, OpenJDK is the official Java reference implementation.

The goal of Java is to make all implementations of Java compatible. Historically, Sun’s trademark license for usage of the Java brand insists that all implementations be compatible. This resulted in a legal dispute with Microsoft after Sun claimed that the Microsoft implementation did not support RMI or JNI and had added platform-specific features of their own. Sun sued in 1997, and, in 2001, won a settlement of US$20 million, as well as a court order enforcing the terms of the license from Sun.[75] As a result, Microsoft no longer ships Java with Windows.

Platform-independent Java is essential to Java EE, and an even more rigorous validation is required to certify an implementation. This environment enables portable server-side applications.

Use outside the Java platform

The Java programming language requires the presence of a software platform in order for compiled programs to be executed.

Oracle supplies the Java platform for use with Java. The Android SDK is an alternative software platform, used primarily for developing Android applications with its own GUI system.

Android

The Android operating system makes extensive use of Java-related technology

The Java language is a key pillar in Android, an open source mobile operating system. Although Android, built on the Linux kernel, is written largely in C, the Android SDK uses the Java language as the basis for Android applications but does not use any of its standard GUI, SE, ME or other established Java standards.[76] The bytecode language supported by the Android SDK is incompatible with Java bytecode and runs on its own virtual machine, optimized for low-memory devices such as smartphones and tablet computers. Depending on the Android version, the bytecode is either interpreted by the Dalvik virtual machine or compiled into native code by the Android Runtime.

Android does not provide the full Java SE standard library, although the Android SDK does include an independent implementation of a large subset of it. It supports Java 6 and some Java 7 features, offering an implementation compatible with the standard library (Apache Harmony).

Controversy

See also: Oracle America, Inc. v. Google, Inc.

The use of Java-related technology in Android led to a legal dispute between Oracle and Google. On May 7, 2012, a San Francisco jury found that if APIs could be copyrighted, then Google had infringed Oracle’s copyrights by the use of Java in Android devices.[77] District Judge William Alsup ruled on May 31, 2012, that APIs cannot be copyrighted,[78] but this was reversed by the United States Court of Appeals for the Federal Circuit in May 2014.[79] On May 26, 2016, the district court decided in favor of Google, ruling the copyright infringement of the Java API in Android constitutes fair use.[80] In March 2018, this ruling was overturned by the Appeals Court, which sent down the case of determining the damages to federal court in San Francisco.[81] Google filed a petition for writ of certiorari with the Supreme Court of the United States in January 2019 to challenge the two rulings that were made by the Appeals Court in Oracle’s favor.[82]” (WP)

See also

Comparison of Java with other languages

References

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Works cited

External links

Wikiversity has learning resources about Java Platform, Enterprise Edition/Java EE Tutorial
  •  The dictionary definition of Java at Wiktionary
  •  Media related to Java at Wikimedia Commons
  •  Java at Wikibooks
  •  Learning materials related to Java at Wikiversity

Fair Use Sources:

Categories
History Software Engineering

Object-Oriented Programming (OOP) – 1967 AD

Return to Timeline of the History of Computers

1967

Object-Oriented Programming

Ole-Johan Dahl (1931–2002), Kristen Nygaard (1926–2002)

“Object-oriented programming (OOP) is a software programming model constructed around objects. This model compartmentalizes data into objects (data fields) and describes object contents and behavior through the declaration of classes (methods).” (TcPd)

“The first programs did important but repetitive tasks, such as printing artillery tables, performing calculations for nuclear weapons, and cracking codes. These programs consisted of loops that executed the same mathematical functions over and over, each time with slightly different parameters. Early business computers performed similar iterative computations on business ledgers and other records, repeatedly reading data from disk, processing it, and saving the results.” (TCB)

“At the Norwegian Computing Center, professors Ole-Johan Dahl and Kristen Nygaard wanted to use their computer to simulate physical systems, in particular ship simulations, and here they found the programming languages developed to enable simple, repetitive tasks to be lacking. So they developed a new way to program and a new computer language, which they called SIMULA 67.” (TCB)

“The key idea of SIMULA was for data representing physical objects to be bundled together with the computer code for acting on that data. For example, a simulation of traffic might have a data type called CAR that might have variables for the car’s location and speed. A special function might handle the car’s behavior when it encountered a traffic light. SIMULA refers to each of these data types as a “class.” A different class called TRUCK might represent trucks. Another key idea was inheritance, which allows classes with shared characteristics to be arranged in a hierarchy. So a TRUCK and a CAR might both inherit from an abstract class called a VEHICLE, which itself might inherit from another abstract class called an OBJECT.” (TCB)

“Today, SIMULA’s style of programming is called object-oriented programming, and SIMULA 67 is recognized as the first object-oriented language. It turns out that the ideas of SIMULA were good for a whole lot more than just writing simulations: practically every modern computer language is object-oriented, including C++, Java, Python, and Go, and today object-oriented programming is the dominant way that software is written.” (TCB)

“OOP features include the following:

  • “Encapsulation: This makes the program structure easier to manage because each object’s implementation and state are hidden behind well-defined boundaries.” (TcPd)
  • “Polymorphism: This means abstract entities are implemented in multiple ways.” (TcPd)
  • “Inheritance: This refers to the hierarchical arrangement of implementation fragments.” (TcPd)

“Object-oriented programming allows for simplified programming. Its benefits include reusability, refactoring, extensibility, maintenance and efficiency.” (TcPd)

“OOP has been the programming model of choice for the last decade or more. OOP’s modular design enables programmers to build software in manageable chunks rather than in large amounts of sequential code.” (TcPd)

“One of the great benefits of OOP is that of scalability, with objects and definitions having no finite limitation. Also, the separation of data from method prevents a common problem found in older linear software languages. If a bug appears in a linear code, it can be translated through a system and create masses of hard-to-trace errors. Conversely, an OOP program, with its separation of method and data, is not susceptible to such proliferated errors.” (TcPd)

“Popular OOP languages include Java, the C-family of languages,VB.NET and Python.” (TcPd)

“So-called “pure” OOP languages include Scala, Ruby, Eiffel, JADE, Smalltalk and Emerald.” (TcPd)

SEE ALSO Programming for Children (1967), C Programming Language (1972)

Programmers create object-oriented programs by designing classes of objects that represent physical objects, processes, or arrangements of data. They then connect the objects with code.

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