The original and reference implementation Java compilers, virtual machines, and class libraries were developed by Sun from 1995. As of May 2007, in compliance with the specifications of the Java Community Process, Sun relicensed most of its Java technologies under the GNU General Public License. Others have also developed alternative implementations of these Sun technologies, such as the GNU Compiler for Java, GNU Classpath, and Dalvik.

History

James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991. Java was originally designed for interactive television, but it was too advanced for the digital cable television industry at the time. The language was initially called ''Oak'' after an oak tree that stood outside Gosling's office; it went by the name ''Green'' later, and was later renamed ''Java'', from Java coffee, said to be consumed in large quantities by the language's creators. Gosling aimed to implement a virtual machine and a language that had a familiar C/C++ style of notation.

Sun Microsystems released the first public implementation as Java 1.0 in 1995. It promised "Write Once, Run Anywhere" (WORA), 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. 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. For example, ''J2EE'' targeted enterprise applications and the greatly stripped-down version ''J2ME'' for mobile applications (Mobile Java). ''J2SE'' designated the Standard Edition. In 2006, for marketing purposes, Sun renamed new ''J2'' versions as ''Java EE'', ''Java ME'', and ''Java SE'', respectively.

In 1997, Sun Microsystems approached the ISO/IEC JTC1 standards body and later the Ecma International to formalize Java, but it soon withdrew from the process. Java remains a ''de facto'' standard, controlled through the Java Community Process. 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. Sun distinguishes between its Software Development Kit (SDK) and Runtime Environment (JRE) (a subset of the SDK); the primary distinction involves the JRE's lack of the compiler, utility programs, and header files.

On November 13, 2006, Sun released much of Java as open source software under the terms of the GNU General Public License (GPL). On May 8, 2007, Sun finished the process, making all of Java'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.

Sun's vice-president Rich Green has said that Sun's ideal role with regards to Java is as an "evangelist."

Following Oracle Corporation's acquisition of Sun Microsystems in 2009–2010, Oracle has described itself as the "steward of Java technology with a relentless commitment to fostering a community of participation and transparency".

Principles

Versions

Practices

Java Platform

One characteristic of Java is portability, which means that computer programs written in the Java language must run similarly on any hardware/operating-system platform. This is achieved by compiling the Java language code to an intermediate representation called Java bytecode, instead of directly to platform-specific machine code. Java bytecode instructions are analogous to machine code, but are intended to be interpreted by a virtual machine (VM) written specifically for the host hardware. End-users commonly use a Java Runtime Environment (JRE) installed on their own machine for standalone Java applications, or in a Web browser for Java applets.

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

A major benefit of using bytecode is porting. However, the overhead of interpretation means that interpreted programs almost always run more slowly than programs compiled to native executables would. Just-in-Time compilers were introduced from an early stage that compile bytecodes to machine code during runtime.

Implementations

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. As a result, Microsoft no longer ships Java with Windows, and in recent versions of Windows, Internet Explorer cannot support Java applets without a third-party plugin. Sun, and others, have made available free Java run-time systems for those and other versions of Windows.

Platform-independent Java is essential to the Java EE strategy, and an even more rigorous validation is required to certify an implementation. This environment enables portable server-side applications, such as Web services, Java Servlets, and Enterprise JavaBeans, as well as with embedded systems based on OSGi, using Embedded Java environments. Through the GlassFish project, Sun is working to create a fully functional, unified open source implementation of the Java EE technologies.

Sun also distributes a superset of the JRE called the Java Development Kit (commonly known as the JDK), which includes development tools such as the Java compiler, Javadoc, Jar, and debugger.

Performance

Programs written in Java have a reputation for being slower and requiring more memory than those written in C. However, Java programs' execution speed improved significantly with the introduction of Just-in-time compilation in 1997/1998 for Java 1.1, the addition of language features supporting better code analysis (such as inner classes, StringBuffer class, optional assertions, etc.), and optimizations in the Java Virtual Machine itself, such as HotSpot becoming the default for Sun's JVM in 2000. Currently, Java 2.0 code has approximately half the performance of C code. However, Java 5.0 has been shown to run at native speeds that sometimes match and occasionally beat the speed of C and C++.

Some platforms offer direct hardware support for Java; there are microcontrollers that can run Java in hardware instead of a software JVM, and ARM based processors can have hardware support for executing Java bytecode through its Jazelle option.

Automatic memory management

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 and/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 and unsigned integers (usually long integers) can be used interchangeably. 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 not objects. Values of primitive types are either stored directly in fields (for objects) or on the stack (for methods) rather than on the heap, as commonly true for objects (but see Escape analysis). This was a conscious decision by Java's designers for performance reasons. Because of this, Java was not considered to be a pure object-oriented programming language. However, as of Java 5.0, autoboxing enables programmers to proceed as if primitive types were instances of their wrapper class.

Java contains multiple types of garbage collectors. By default, HotSpot uses the Concurrent Mark Sweep collector, also known as the CMS Garbage Collector. However, there are also several other garbage collectors that can be used to manage the Heap. For 90% of applications in Java, the CMS Garbage Collector is good enough.

Syntax

The syntax of Java is largely derived from C++. Unlike C++, which combines the syntax for structured, generic, and object-oriented programming, Java was built almost exclusively as an object-oriented language. All code is written inside a class, and everything is an object, with the exception of the primitive data types (integers, floating-point numbers, boolean values, and characters), which are not classes for performance reasons.

Unlike C++, Java does not support operator overloading or multiple inheritance for ''classes''. This simplifies the language and aids in preventing potential errors and anti-pattern design.

Java uses similar commenting methods to 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 compile documentation for the program.

Example:

// 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. */

/** * This is an example of a Javadoc comment; Javadoc can compile documentation * from this text. */

Examples

Hello world

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 named HelloWorldApp.class. Only then can it be executed, or 'launched'. The Java source file may only contain one public class but can contain multiple classes with less than public access and any number of public inner classes.

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.

The keyword static 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.

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 JavaBean 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 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 (the args parameter is still an array of String objects), but 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 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 class defines a public static field called . The out object is an instance of the class and provides many methods for printing data to standard out, including which also appends a new line to the passed string.

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

A more comprehensive example

public class OddEven { // "input" is the number that the user gives to the computer private int input; // a whole number("int" means integer)

/* * This is the constructor method. It gets called when an object of the OddEven type * is being created. */ public OddEven() { /* * In most Java programs constructors can initialize objects with default values, or create * other objects that this object might use to perform its functions. In some Java programs, the * constructor may simply be an empty function if nothing needs to be initialized prior to the * functioning of the object. In this program's case, an empty constructor would suffice, even if * it is empty. A constructor must exist, however if the user doesn't put one in then the compiler * will create an empty one. */ }

// This is the main method. It gets called when this class is run through a Java interpreter. public static void main(String[] args) { /* * This line of code creates a new instance of this class called "number" (also known as an * Object) and initializes it by calling the constructor. The next line of code calls * the "showDialog()" method, which brings up a prompt to ask you for a number */ OddEven number = new OddEven(); number.showDialog(); }

public void showDialog() { /* * "try" makes sure nothing goes wrong. If something does, * the interpreter skips to "catch" to see what it should do. */ try { /* * The code below brings up a JOptionPane, which is a dialog box * The String returned by the "showInputDialog()" method is converted into * an integer, making the program treat it as a number instead of a word. * After that, this method calls a second method, calculate() that will * display either "Even" or "Odd." */ input = Integer.parseInt(JOptionPane.showInputDialog("Please Enter A Number")); calculate(); } catch (NumberFormatException e) { /* * Getting in the catch block means that there was a problem with the format of * the number. Probably some letters were typed in instead of a number. */ System.err.println("ERROR: Invalid input. Please type in a numerical value."); } }

/* * When this gets called, it sends a message to the interpreter. * The interpreter usually shows it on the command prompt (For Windows users) * or the terminal (For *nix users).(Assuming it's open) */ private void calculate() { if (input % 2 == 0) { System.out.println("Even"); } else { System.out.println("Odd"); } } }

The import statement imports the class from the package.

Special classes

Applet

Java applets are programs that are embedded in other applications, typically in a Web page displayed in a Web browser.

// Hello.java import javax.swing.JApplet; import java.awt.Graphics;

public class Hello extends JApplet {

public void paintComponent(Graphics g) { g.drawString("Hello, world!", 65, 95); }

}

The import statements direct the Java compiler to include the and classes in the compilation. The import statement allows these classes to be referenced in the source code using the ''simple class name'' (i.e. JApplet) instead of the ''fully qualified class name'' (i.e. javax.swing.JApplet).

The Hello class extends (subclasses) the JApplet (Java Applet) class; the JApplet class provides the framework for the host application to display and control the lifecycle of the applet. The JApplet class is a JComponent (Java Graphical Component) which provides the applet with the capability to display a graphical user interface (GUI) and respond to user events.

The Hello class overrides the method (additionally indicated with the annotation, supported as of JDK 1.5, Override) inherited from the superclass to provide the code to display the applet. The paintComponent() method is passed a Graphics object that contains the graphic context used to display the applet. The paintComponent() method calls the graphic context method to display the "Hello, world!" string at a pixel offset of (65, 95) from the upper-left corner in the applet's display.

An applet is placed in an HTML document using the HTML element. The applet tag has three attributes set: code="Hello" specifies the name of the JApplet class and width="200" height="200" sets the pixel width and height of the applet. Applets may also be embedded in HTML using either the object or embed element, although support for these elements by Web browsers is inconsistent. However, the applet tag is deprecated, so the object tag is preferred where supported.

The host application, typically a Web browser, instantiates the Hello applet and creates an for the applet. Once the applet has initialized itself, it is added to the AWT display hierarchy. The paintComponent() method is called by the AWT event dispatching thread whenever the display needs the applet to draw itself.

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 (typically HTML pages) to requests (typically HTTP requests) from clients. A servlet can almost be thought of as an applet that runs on the server side—without a face.

// Hello.java import java.io.*; import javax.servlet.*;

public class Hello extends GenericServlet { public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); final PrintWriter pw = response.getWriter(); try { pw.println("Hello, world!"); } finally { pw.close(); } } }

The import statements direct the Java compiler to include all of the public classes and interfaces from the and packages in the compilation.

The Hello class extends the class; the GenericServlet class provides the interface for the server to forward requests to the servlet and control the servlet's lifecycle.

The Hello class overrides the method defined by the interface to provide the code for the service request handler. The service() method is passed a object that contains the request from the client and a object used to create the response returned to the client. The service() method declares that it throws the exceptions and if a problem prevents it from responding to the request.

The method in the response object is called to set the MIME content type of the returned data to "text/html". The method in the response returns a object that is used to write the data that is sent to the client. The method is called to write the "Hello, world!" string to the response and then the method is called to close the print writer, which causes the data that has been written to the stream to be returned to the client.

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.

Swing application

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 Windows, GTK+ and Motif are supplied by Sun. Apple also provides an Aqua look and feel for Mac OS X. 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.

This example Swing application creates a single window with "Hello, world!" inside:

// Hello.java (Java SE 5) import javax.swing.*;

public class Hello extends JFrame { public Hello() { super("hello"); setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE); add(new JLabel("Hello, world!")); pack(); setVisible(true);

}

public static void main(String[] args) { new Hello(); } }

The first import includes all of the public classes and interfaces from the package.

The Hello class extends the class; the JFrame class implements a window with a title bar and a close control.

The Hello() constructor initializes the frame by first calling the superclass constructor, passing the parameter "hello", which is used as the window's title. It then calls the method inherited from JFrame to set the default operation when the close control on the title bar is selected to — this causes the JFrame to be disposed of when the frame is closed (as opposed to merely hidden), which allows the JVM to exit and the program to terminate. Next, a is created for the string "Hello, world!" and the method inherited from the superclass is called to add the label to the frame. The method inherited from the superclass is called to size the window and lay out its contents.

The main() method is called by the JVM when the program starts. It instantiates a new Hello frame and causes it to be displayed by calling the method inherited from the superclass with the boolean parameter true. Once the frame is displayed, exiting the main method does not cause the program to terminate because the AWT event dispatching thread remains active until all of the Swing top-level windows have been disposed.

Generics

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 a large number of container classes, each containing almost identical code.

Criticism

A number of criticisms have been leveled at Java for various design choices in the language and platform. Such criticisms include the implementation of generics, the handling of unsigned numbers, the implementation of floating-point arithmetic, and security vulnerabilities.

Class libraries

Java libraries are the compiled bytecodes of source code developed by the JRE implementor to support application development in Java. Examples of these libraries are:

* The core libraries, which include:

** Collection libraries that implement data structures such as lists, dictionaries, trees, sets, queues and double-ended queue, or stacks

** XML Processing (Parsing, Transforming, Validating) libraries

** Security

** Internationalization and localization libraries

* The integration libraries, which allow the application writer to communicate with external systems. These libraries include:

** The Java Database Connectivity (JDBC) API for database access

** Java Naming and Directory Interface (JNDI) for lookup and discovery

** RMI and CORBA for distributed application development

** JMX for managing and monitoring applications

* User interface libraries, which include:

** The (heavyweight, or native) Abstract Window Toolkit (AWT), which provides GUI components, the means for laying out those components and the means for handling events from those components

** The (lightweight) Swing libraries, which are built on AWT but provide (non-native) implementations of the AWT widgetry

** APIs for audio capture, processing, and playback

A platform dependent implementation of Java Virtual Machine (JVM) that is the means by which the byte codes of the Java libraries and third party applications are executed

Plugins, which enable applets to be run in Web browsers

Java Web Start, which allows Java applications to be efficiently distributed to end-users across the Internet

Licensing and documentation.

Documentation

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

Editions

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:

Java Card for smartcards.

Java Platform, Micro Edition (Java ME) — targeting environments with limited resources.

Java Platform, Standard Edition (Java SE) — targeting workstation environments.

Java Platform, Enterprise Edition (Java EE) — targeting large distributed enterprise or Internet environments.

The classes in the Java APIs are organized into separate groups called packages. Each package contains a set of related interfaces, classes and exceptions. Refer to the separate platforms for a description of the packages available.

The set of APIs is controlled by Sun Microsystems in cooperation with others through the Java Community Process program. Companies or individuals participating in this process can influence the design and development of the APIs. This process has been a subject of controversy.

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

Notes

See also

Comparison of programming languages

Comparison of Java and C++

Comparison of Java and C#

JavaOne

Javapedia

List of Java virtual machines

List of Java APIs

List of JVM languages

Java version history

Threads in the Java programming language

C#

References

Gosling, James, ''A brief history of the Green project''. Java.net, no date [ca. Q1/1998]. Retrieved April 29, 2007.

External links

java.com - Java for end-users

Oracle's Developer Resources for Java Technology.

A Brief History of the Green Project

Michael O'Connell: Java: The Inside Story, SunWord, July 1995.

Patrick Naughton: Java Was Strongly Influenced by Objective-C (no date).

David Bank: The Java Saga, ''Wired'' Issue 3.12 (December 1995).

Shahrooz Feizabadi: A history of Java in: Marc Abrams, ed., ''World Wide Web – Beyond the Basics'', Prentice Hall, 1998.

Patrick Naughton: The Long Strange Trip to Java, March 18, 1996.

Open University (UK): M254 Java Everywhere (free open content documents).

is-research GmbH: List of programming languages for a Java Virtual Machine.

How Java's Floating-Point Hurts Everyone Everywhere, by W. Kahan and Joseph D. Darcy, University of California, Berkeley.

Lyes Hassaine: Object Oriented Programming vs. Procedural Programming, June 17, 2011.

Category:C programming language family Category:Class-based programming languages Category:Concurrent programming languages Category:Cross-platform software Programming language Programming language Category:JVM programming languages Category:Object-oriented programming languages Category:Programming languages created in 1995 Category:Sun Microsystems

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This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.

A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely.

The earliest programming languages predate the invention of the computer, and were used to direct the behavior of machines such as Jacquard looms and player pianos. Thousands of different programming languages have been created, mainly in the computer field, with many more being created every year. Most programming languages describe computation in an imperative style, i.e., as a sequence of commands, although some languages, such as those that support functional programming or logic programming, use alternative forms of description.

A programming language is usually split into the two components of syntax (form) and semantics (meaning). Some languages are defined by a specification document (for example, the C programming language is specified by an ISO Standard), while other languages, such as Perl, have a dominant implementation that is used as a reference.

Definitions

A programming language is a notation for writing programs, which are specifications of a computation or algorithm. Some, but not all, authors restrict the term "programming language" to those languages that can express ''all'' possible algorithms. Traits often considered important for what constitutes a programming language include: ''Function and target:'' A ''computer programming language'' is a language used to write computer programs, which involve a computer performing some kind of computation or algorithm and possibly control external devices such as printers, disk drives, robots, and so on. For example PostScript programs are frequently created by another program to control a computer printer or display. More generally, a programming language may describe computation on some, possibly abstract, machine. It is generally accepted that a complete specification for a programming language includes a description, possibly idealized, of a machine or processor for that language. In most practical contexts, a programming language involves a computer; consequently programming languages are usually defined and studied this way. Programming languages differ from natural languages in that natural languages are only used for interaction between people, while programming languages also allow humans to communicate instructions to machines. ''Abstractions:'' Programming languages usually contain abstractions for defining and manipulating data structures or controlling the flow of execution. The practical necessity that a programming language support adequate abstractions is expressed by the abstraction principle; this principle is sometimes formulated as recommendation to the programmer to make proper use of such abstractions. ''Expressive power:'' The theory of computation classifies languages by the computations they are capable of expressing. All Turing complete languages can implement the same set of algorithms. ANSI/ISO SQL and Charity are examples of languages that are not Turing complete, yet often called programming languages.

Markup languages like XML, HTML or troff, which define structured data, are not generally considered programming languages. Programming languages may, however, share the syntax with markup languages if a computational semantics is defined. XSLT, for example, is a Turing complete XML dialect. Moreover, LaTeX, which is mostly used for structuring documents, also contains a Turing complete subset.

The term ''computer language'' is sometimes used interchangeably with programming language. However, the usage of both terms varies among authors, including the exact scope of each. One usage describes programming languages as a subset of computer languages. In this vein, languages used in computing that have a different goal than expressing computer programs are generically designated computer languages. For instance, markup languages are sometimes referred to as computer languages to emphasize that they are not meant to be used for programming. Another usage regards programming languages as theoretical constructs for programming abstract machines, and computer languages as the subset thereof that runs on physical computers, which have finite hardware resources. John C. Reynolds emphasizes that formal specification languages are just as much programming languages as are the languages intended for execution. He also argues that textual and even graphical input formats that affect the behavior of a computer are programming languages, despite the fact they are commonly not Turing-complete, and remarks that ignorance of programming language concepts is the reason for many flaws in input formats.

Elements

All programming languages have some primitive building blocks for the description of data and the processes or transformations applied to them (like the addition of two numbers or the selection of an item from a collection). These primitives are defined by syntactic and semantic rules which describe their structure and meaning respectively.

Syntax

A programming language's surface form is known as its syntax. Most programming languages are purely textual; they use sequences of text including words, numbers, and punctuation, much like written natural languages. On the other hand, there are some programming languages which are more graphical in nature, using visual relationships between symbols to specify a program.

The syntax of a language describes the possible combinations of symbols that form a syntactically correct program. The meaning given to a combination of symbols is handled by semantics (either formal or hard-coded in a reference implementation). Since most languages are textual, this article discusses textual syntax.

Programming language syntax is usually defined using a combination of regular expressions (for lexical structure) and Backus–Naur Form (for grammatical structure). Below is a simple grammar, based on Lisp:

expression ::= atom | list
atom ::= number | symbol
number ::= [+-]?['0'-'9']+
symbol ::= ['A'-'Z''a'-'z'].*
list ::= '(' expression* ')'

This grammar specifies the following:

an ''expression'' is either an ''atom'' or a ''list'';

an ''atom'' is either a ''number'' or a ''symbol'';

a ''number'' is an unbroken sequence of one or more decimal digits, optionally preceded by a plus or minus sign;

a ''symbol'' is a letter followed by zero or more of any characters (excluding whitespace); and

a ''list'' is a matched pair of parentheses, with zero or more ''expressions'' inside it.

The following are examples of well-formed token sequences in this grammar: '12345', '()', '(a b c232 (1))'

Not all syntactically correct programs are semantically correct. Many syntactically correct programs are nonetheless ill-formed, per the language's rules; and may (depending on the language specification and the soundness of the implementation) result in an error on translation or execution. In some cases, such programs may exhibit undefined behavior. Even when a program is well-defined within a language, it may still have a meaning that is not intended by the person who wrote it.

Using natural language as an example, it may not be possible to assign a meaning to a grammatically correct sentence or the sentence may be false:

"Colorless green ideas sleep furiously." is grammatically well-formed but has no generally accepted meaning.

"John is a married bachelor." is grammatically well-formed but expresses a meaning that cannot be true.

The following C language fragment is syntactically correct, but performs operations that are not semantically defined (the operation *p >> 4 has no meaning for a value having a complex type and p->im is not defined because the value of p is the null pointer):

complex *p = NULL; complex abs_p = sqrt(*p >> 4 + p->im);

If the type declaration on the first line were omitted, the program would trigger an error on compilation, as the variable "p" would not be defined. But the program would still be syntactically correct, since type declarations provide only semantic information.

The grammar needed to specify a programming language can be classified by its position in the Chomsky hierarchy. The syntax of most programming languages can be specified using a Type-2 grammar, i.e., they are context-free grammars. Some languages, including Perl and Lisp, contain constructs that allow execution during the parsing phase. Languages that have constructs that allow the programmer to alter the behavior of the parser make syntax analysis an undecidable problem, and generally blur the distinction between parsing and execution. In contrast to Lisp's macro system and Perl's BEGIN blocks, which may contain general computations, C macros are merely string replacements, and do not require code execution.

Semantics

The term ''semantics'' refers to the meaning of languages, as opposed to their form (syntax).

Static semantics

The static semantics defines restrictions on the structure of valid texts that are hard or impossible to express in standard syntactic formalisms. For compiled languages, static semantics essentially include those semantic rules that can be checked at compile time. Examples include checking that every identifier is declared before it is used (in languages that require such declarations) or that the labels on the arms of a case statement are distinct. Many important restrictions of this type, like checking that identifiers are used in the appropriate context (e.g. not adding an integer to a function name), or that subroutine calls have the appropriate number and type of arguments, can be enforced by defining them as rules in a logic called a type system. Other forms of static analyses like data flow analysis may also be part of static semantics. Newer programming languages like Java and C# have definite assignment analysis, a form of data flow analysis, as part of their static semantics.

Dynamic semantics

Once data has been specified, the machine must be instructed to perform operations on the data. For example, the semantics may define the strategy by which expressions are evaluated to values, or the manner in which control structures conditionally execute statements. The ''dynamic semantics'' (also known as ''execution semantics'') of a language defines how and when the various constructs of a language should produce a program behavior. There are many ways of defining execution semantics. Natural language is often used to specify the execution semantics of languages commonly used in practice. A significant amount of academic research went into formal semantics of programming languages, which allow execution semantics to be specified in a formal manner. Results from this field of research have seen limited application to programming language design and implementation outside academia.

Type system

A type system defines how a programming language classifies values and expressions into ''types'', how it can manipulate those types and how they interact. The goal of a type system is to verify and usually enforce a certain level of correctness in programs written in that language by detecting certain incorrect operations. Any decidable type system involves a trade-off: while it rejects many incorrect programs, it can also prohibit some correct, albeit unusual programs. In order to bypass this downside, a number of languages have ''type loopholes'', usually unchecked casts that may be used by the programmer to explicitly allow a normally disallowed operation between different types. In most typed languages, the type system is used only to type check programs, but a number of languages, usually functional ones, infer types, relieving the programmer from the need to write type annotations. The formal design and study of type systems is known as ''type theory''.

Typed versus untyped languages

A language is ''typed'' if the specification of every operation defines types of data to which the operation is applicable, with the implication that it is not applicable to other types. For example, the data represented by "this text between the quotes" is a string. In most programming languages, dividing a number by a string has no meaning. Most modern programming languages will therefore reject any program attempting to perform such an operation. In some languages, the meaningless operation will be detected when the program is compiled ("static" type checking), and rejected by the compiler, while in others, it will be detected when the program is run ("dynamic" type checking), resulting in a runtime exception.

A special case of typed languages are the ''single-type'' languages. These are often scripting or markup languages, such as REXX or SGML, and have only one data type—most commonly character strings which are used for both symbolic and numeric data.

In contrast, an ''untyped language'', such as most assembly languages, allows any operation to be performed on any data, which are generally considered to be sequences of bits of various lengths. High-level languages which are untyped include BCPL and some varieties of Forth.

In practice, while few languages are considered typed from the point of view of type theory (verifying or rejecting ''all'' operations), most modern languages offer a degree of typing. Many production languages provide means to bypass or subvert the type system.

Static versus dynamic typing

In ''static typing'', all expressions have their types determined prior to when the program is executed, typically at compile-time. For example, 1 and (2+2) are integer expressions; they cannot be passed to a function that expects a string, or stored in a variable that is defined to hold dates.

Statically typed languages can be either ''manifestly typed'' or ''type-inferred''. In the first case, the programmer must explicitly write types at certain textual positions (for example, at variable declarations). In the second case, the compiler ''infers'' the types of expressions and declarations based on context. Most mainstream statically typed languages, such as C++, C# and Java, are manifestly typed. Complete type inference has traditionally been associated with less mainstream languages, such as Haskell and ML. However, many manifestly typed languages support partial type inference; for example, Java and C# both infer types in certain limited cases.

''Dynamic typing'', also called ''latent typing'', determines the type-safety of operations at runtime; in other words, types are associated with ''runtime values'' rather than ''textual expressions''. As with type-inferred languages, dynamically typed languages do not require the programmer to write explicit type annotations on expressions. Among other things, this may permit a single variable to refer to values of different types at different points in the program execution. However, type errors cannot be automatically detected until a piece of code is actually executed, potentially making debugging more difficult. Ruby, Lisp, JavaScript, and Python are dynamically typed.

Weak and strong typing

''Weak typing'' allows a value of one type to be treated as another, for example treating a string as a number. This can occasionally be useful, but it can also allow some kinds of program faults to go undetected at compile time and even at run-time.

''Strong typing'' prevents the above. An attempt to perform an operation on the wrong type of value raises an error. Strongly typed languages are often termed ''type-safe'' or ''safe''.

An alternative definition for "weakly typed" refers to languages, such as Perl and JavaScript, which permit a large number of implicit type conversions. In JavaScript, for example, the expression 2 * x implicitly converts x to a number, and this conversion succeeds even if x is null, undefined, an Array, or a string of letters. Such implicit conversions are often useful, but they can mask programming errors. ''Strong'' and ''static'' are now generally considered orthogonal concepts, but usage in the literature differs. Some use the term ''strongly typed'' to mean ''strongly, statically typed'', or, even more confusingly, to mean simply ''statically typed''. Thus C has been called both strongly typed and weakly, statically typed.

Standard library and run-time system

Most programming languages have an associated core library (sometimes known as the 'standard library', especially if it is included as part of the published language standard), which is conventionally made available by all implementations of the language. Core libraries typically include definitions for commonly used algorithms, data structures, and mechanisms for input and output.

A language's core library is often treated as part of the language by its users, although the designers may have treated it as a separate entity. Many language specifications define a core that must be made available in all implementations, and in the case of standardized languages this core library may be required. The line between a language and its core library therefore differs from language to language. Indeed, some languages are designed so that the meanings of certain syntactic constructs cannot even be described without referring to the core library. For example, in Java, a string literal is defined as an instance of the java.lang.String class; similarly, in Smalltalk, an anonymous function expression (a "block") constructs an instance of the library's BlockContext class. Conversely, Scheme contains multiple coherent subsets that suffice to construct the rest of the language as library macros, and so the language designers do not even bother to say which portions of the language must be implemented as language constructs, and which must be implemented as parts of a library.

Design and implementation

Programming languages share properties with natural languages related to their purpose as vehicles for communication, having a syntactic form separate from its semantics, and showing ''language families'' of related languages branching one from another. But as artificial constructs, they also differ in fundamental ways from languages that have evolved through usage. A significant difference is that a programming language can be fully described and studied in its entirety, since it has a precise and finite definition. By contrast, natural languages have changing meanings given by their users in different communities. While constructed languages are also artificial languages designed from the ground up with a specific purpose, they lack the precise and complete semantic definition that a programming language has.

Many programming languages have been designed from scratch, altered to meet new needs, and combined with other languages. Many have eventually fallen into disuse. Although there have been attempts to design one "universal" programming language that serves all purposes, all of them have failed to be generally accepted as filling this role. The need for diverse programming languages arises from the diversity of contexts in which languages are used:

Programs range from tiny scripts written by individual hobbyists to huge systems written by hundreds of programmers.

Programmers range in expertise from novices who need simplicity above all else, to experts who may be comfortable with considerable complexity.

Programs must balance speed, size, and simplicity on systems ranging from microcontrollers to supercomputers.

Programs may be written once and not change for generations, or they may undergo continual modification.

Finally, programmers may simply differ in their tastes: they may be accustomed to discussing problems and expressing them in a particular language.

One common trend in the development of programming languages has been to add more ability to solve problems using a higher level of abstraction. The earliest programming languages were tied very closely to the underlying hardware of the computer. As new programming languages have developed, features have been added that let programmers express ideas that are more remote from simple translation into underlying hardware instructions. Because programmers are less tied to the complexity of the computer, their programs can do more computing with less effort from the programmer. This lets them write more functionality per time unit.

Natural language processors have been proposed as a way to eliminate the need for a specialized language for programming. However, this goal remains distant and its benefits are open to debate. Edsger W. Dijkstra took the position that the use of a formal language is essential to prevent the introduction of meaningless constructs, and dismissed natural language programming as "foolish". Alan Perlis was similarly dismissive of the idea. Hybrid approaches have been taken in Structured English and SQL.

A language's designers and users must construct a number of artifacts that govern and enable the practice of programming. The most important of these artifacts are the language ''specification'' and ''implementation''.

Specification

The specification of a programming language is intended to provide a definition that the language users and the implementors can use to determine whether the behavior of a program is correct, given its source code.

A programming language specification can take several forms, including the following: An explicit definition of the syntax, static semantics, and execution semantics of the language. While syntax is commonly specified using a formal grammar, semantic definitions may be written in natural language (e.g., as in the C language), or a formal semantics (e.g., as in Standard ML and Scheme specifications).

A description of the behavior of a translator for the language (e.g., the C++ and Fortran specifications). The syntax and semantics of the language have to be inferred from this description, which may be written in natural or a formal language.

A ''reference'' or ''model'' implementation, sometimes written in the language being specified (e.g., Prolog or ANSI REXX). The syntax and semantics of the language are explicit in the behavior of the reference implementation.

Implementation

An implementation of a programming language provides a way to execute that program on one or more configurations of hardware and software. There are, broadly, two approaches to programming language implementation: ''compilation'' and ''interpretation''. It is generally possible to implement a language using either technique.

The output of a compiler may be executed by hardware or a program called an interpreter. In some implementations that make use of the interpreter approach there is no distinct boundary between compiling and interpreting. For instance, some implementations of BASIC compile and then execute the source a line at a time.

Programs that are executed directly on the hardware usually run several orders of magnitude faster than those that are interpreted in software.

One technique for improving the performance of interpreted programs is just-in-time compilation. Here the virtual machine, just before execution, translates the blocks of bytecode which are going to be used to machine code, for direct execution on the hardware.

Usage

Thousands of different programming languages have been created, mainly in the computing field. Programming languages differ from most other forms of human expression in that they require a greater degree of precision and completeness.

When using a natural language to communicate with other people, human authors and speakers can be ambiguous and make small errors, and still expect their intent to be understood. However, figuratively speaking, computers "do exactly what they are told to do", and cannot "understand" what code the programmer intended to write. The combination of the language definition, a program, and the program's inputs must fully specify the external behavior that occurs when the program is executed, within the domain of control of that program. On the other hand, ideas about an algorithm can be communicated to humans without the precision required for execution by using pseudocode, which interleaves natural language with code written in a programming language.

A programming language provides a structured mechanism for defining pieces of data, and the operations or transformations that may be carried out automatically on that data. A programmer uses the abstractions present in the language to represent the concepts involved in a computation. These concepts are represented as a collection of the simplest elements available (called primitives). ''Programming'' is the process by which programmers combine these primitives to compose new programs, or adapt existing ones to new uses or a changing environment.

Programs for a computer might be executed in a batch process without human interaction, or a user might type commands in an interactive session of an interpreter. In this case the "commands" are simply programs, whose execution is chained together. When a language is used to give commands to a software application (such as a shell) it is called a scripting language.

Measuring language usage

It is difficult to determine which programming languages are most widely used, and what usage means varies by context. One language may occupy the greater number of programmer hours, a different one have more lines of code, and a third utilize the most CPU time. Some languages are very popular for particular kinds of applications. For example, COBOL is still strong in the corporate data center, often on large mainframes; FORTRAN in scientific and engineering applications; and C in embedded applications and operating systems. Other languages are regularly used to write many different kinds of applications.

Various methods of measuring language popularity, each subject to a different bias over what is measured, have been proposed: counting the number of job advertisements that mention the language the number of books sold that teach or describe the language estimates of the number of existing lines of code written in the language—which may underestimate languages not often found in public searches

counts of language references (i.e., to the name of the language) found using a web search engine.

Combining and averaging information from various internet sites, langpop.com claims that in 2008 the 10 most cited programming languages are (in alphabetical order): C, C++, C#, Java, JavaScript, Perl, PHP, Python, Ruby, and SQL.

Taxonomies

There is no overarching classification scheme for programming languages. A given programming language does not usually have a single ancestor language. Languages commonly arise by combining the elements of several predecessor languages with new ideas in circulation at the time. Ideas that originate in one language will diffuse throughout a family of related languages, and then leap suddenly across familial gaps to appear in an entirely different family.

The task is further complicated by the fact that languages can be classified along multiple axes. For example, Java is both an object-oriented language (because it encourages object-oriented organization) and a concurrent language (because it contains built-in constructs for running multiple threads in parallel). Python is an object-oriented scripting language.

In broad strokes, programming languages divide into ''programming paradigms'' and a classification by ''intended domain of use''. Traditionally, programming languages have been regarded as describing computation in terms of imperative sentences, i.e. issuing commands. These are generally called imperative programming languages. A great deal of research in programming languages has been aimed at blurring the distinction between a program as a set of instructions and a program as an assertion about the desired answer, which is the main feature of declarative programming. More refined paradigms include procedural programming, object-oriented programming, functional programming, and logic programming; some languages are hybrids of paradigms or multi-paradigmatic. An assembly language is not so much a paradigm as a direct model of an underlying machine architecture. By purpose, programming languages might be considered general purpose, system programming languages, scripting languages, domain-specific languages, or concurrent/distributed languages (or a combination of these). Some general purpose languages were designed largely with educational goals.

A programming language may also be classified by factors unrelated to programming paradigm. For instance, most programming languages use English language keywords, while a minority do not. Other languages may be classified as being esoteric or not.

History

Early developments

The first programming languages predate the modern computer. The 19th century had "programmable" looms and player piano scrolls which implemented what are today recognized as examples of domain-specific languages. By the beginning of the twentieth century, punch cards encoded data and directed mechanical processing. In the 1930s and 1940s, the formalisms of Alonzo Church's lambda calculus and Alan Turing's Turing machines provided mathematical abstractions for expressing algorithms; the lambda calculus remains influential in language design.

In the 1940s, the first electrically powered digital computers were created. The first high-level programming language to be designed for a computer was Plankalkül, developed for the German Z3 by Konrad Zuse between 1943 and 1945. However, it was not implemented until 1998 and 2000.

Programmers of early 1950s computers, notably UNIVAC I and IBM 701, used machine language programs, that is, the first generation language (1GL). 1GL programming was quickly superseded by similarly machine-specific, but mnemonic, second generation languages (2GL) known as assembly languages or "assembler". Later in the 1950s, assembly language programming, which had evolved to include the use of macro instructions, was followed by the development of "third generation" programming languages (3GL), such as FORTRAN, LISP, and COBOL. 3GLs are more abstract and are "portable", or at least implemented similarly on computers that do not support the same native machine code. Updated versions of all of these 3GLs are still in general use, and each has strongly influenced the development of later languages. At the end of the 1950s, the language formalized as ALGOL 60 was introduced, and most later programming languages are, in many respects, descendants of Algol. The format and use of the early programming languages was heavily influenced by the constraints of the interface.

Refinement

The period from the 1960s to the late 1970s brought the development of the major language paradigms now in use, though many aspects were refinements of ideas in the very first Third-generation programming languages: APL introduced ''array programming'' and influenced functional programming.

PL/I (NPL) was designed in the early 1960s to incorporate the best ideas from FORTRAN and COBOL.

In the 1960s, Simula was the first language designed to support ''object-oriented programming''; in the mid-1970s, Smalltalk followed with the first "purely" object-oriented language.

C was developed between 1969 and 1973 as a ''system programming'' language, and remains popular.

Prolog, designed in 1972, was the first ''logic programming'' language.

In 1978, ML built a polymorphic type system on top of Lisp, pioneering ''statically typed functional programming'' languages.

Each of these languages spawned an entire family of descendants, and most modern languages count at least one of them in their ancestry.

The 1960s and 1970s also saw considerable debate over the merits of ''structured programming'', and whether programming languages should be designed to support it. Edsger Dijkstra, in a famous 1968 letter published in the Communications of the ACM, argued that GOTO statements should be eliminated from all "higher level" programming languages.

The 1960s and 1970s also saw expansion of techniques that reduced the footprint of a program as well as improved productivity of the programmer and user. The card deck for an early 4GL was a lot smaller for the same functionality expressed in a 3GL deck.

Consolidation and growth

The 1980s were years of relative consolidation. C++ combined object-oriented and systems programming. The United States government standardized Ada, a systems programming language derived from Pascal and intended for use by defense contractors. In Japan and elsewhere, vast sums were spent investigating so-called "fifth generation" languages that incorporated logic programming constructs. The functional languages community moved to standardize ML and Lisp. Rather than inventing new paradigms, all of these movements elaborated upon the ideas invented in the previous decade.

One important trend in language design for programming large-scale systems during the 1980s was an increased focus on the use of ''modules'', or large-scale organizational units of code. Modula-2, Ada, and ML all developed notable module systems in the 1980s, although other languages, such as PL/I, already had extensive support for modular programming. Module systems were often wedded to generic programming constructs.

The rapid growth of the Internet in the mid-1990s created opportunities for new languages. Perl, originally a Unix scripting tool first released in 1987, became common in dynamic websites. Java came to be used for server-side programming, and bytecode virtual machines became popular again in commercial settings with their promise of "Write once, run anywhere" (UCSD Pascal had been popular for a time in the early 1980s). These developments were not fundamentally novel, rather they were refinements to existing languages and paradigms, and largely based on the C family of programming languages.

Programming language evolution continues, in both industry and research. Current directions include security and reliability verification, new kinds of modularity (mixins, delegates, aspects), and database integration such as Microsoft's LINQ.

The 4GLs are examples of languages which are domain-specific, such as SQL, which manipulates and returns sets of data rather than the scalar values which are canonical to most programming languages. Perl, for example, with its 'here document' can hold multiple 4GL programs, as well as multiple JavaScript programs, in part of its own perl code and use variable interpolation in the 'here document' to support multi-language programming.

See also

Comparison of programming languages (basic instructions)

Comparison of programming languages

Computer programming

Computer science and Outline of computer science

Educational programming language

Invariant based programming

Lists of programming languages

List of programming language researchers

Literate programming

Dialect (computing)

Programming language theory

Pseudocode

Scientific language

Software engineering and List of software engineering topics

References

Further reading

Harold Abelson and Gerald Jay Sussman. ''Structure and Interpretation of Computer Programs'' (2nd ed.), The MIT Press 1996.

Raphael Finkel: ''Advanced Programming Language Design'', Addison Wesley 1995.

Daniel P. Friedman, Mitchell Wand, Christopher T. Haynes: ''Essentials of Programming Languages'', The MIT Press 2001.

Maurizio Gabbrielli and Simone Martini: "Programming Languages: Principles and Paradigms", Springer, 2010.

David Gelernter, Suresh Jagannathan: ''Programming Linguistics'', The MIT Press 1990.

Ellis Horowitz (ed.): ''Programming Languages, a Grand Tour'' (3rd ed.), 1987.

Ellis Horowitz: ''Fundamentals of Programming Languages'', 1989.

Shriram Krishnamurthi: ''Programming Languages: Application and Interpretation'', online publication.

Bruce J. MacLennan: ''Principles of Programming Languages: Design, Evaluation, and Implementation'', Oxford University Press 1999.

John C. Mitchell: ''Concepts in Programming Languages'', Cambridge University Press 2002.

Benjamin C. Pierce: ''Types and Programming Languages'', The MIT Press 2002.

Terrence W. Pratt and Marvin V. Zelkowitz: ''Programming Languages: Design and Implementation'' (4th ed.), Prentice Hall 2000.

Peter H. Salus. ''Handbook of Programming Languages'' (4 vols.). Macmillan 1998.

Ravi Sethi: ''Programming Languages: Concepts and Constructs'', 2nd ed., Addison-Wesley 1996.

Michael L. Scott: ''Programming Language Pragmatics'', Morgan Kaufmann Publishers 2005.

Robert W. Sebesta: ''Concepts of Programming Languages'', 9th ed., Addison Wesley 2009.

Franklyn Turbak and David Gifford with Mark Sheldon: ''Design Concepts in Programming Languages'', The MIT Press 2009.

Peter Van Roy and Seif Haridi. ''Concepts, Techniques, and Models of Computer Programming'', The MIT Press 2004.

David A. Watt. ''Programming Language Concepts and Paradigms''. Prentice Hall 1990.

David A. Watt and Muffy Thomas. ''Programming Language Syntax and Semantics''. Prentice Hall 1991.

David A. Watt. ''Programming Language Processors''. Prentice Hall 1993.

David A. Watt. ''Programming Language Design Concepts''. John Wiley & Sons 2004.

External links

99 Bottles of Beer A collection of implementations in many languages.

Category:Notation

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Name	Larry Wall
Birth date	September 27, 1954
Known for	Perl
alma mater	Seattle Pacific University
Children	4
Spouse	Gloria Wall
Religion	International Church of the Nazarene
Nationality	American
Occupation	Programmer, Author
Website	www.wall.org/~larry/ }}

Larry Wall (born September 27, 1954) is a programmer and author, most widely known for his creation of the Perl programming language in 1987.

Education

Wall earned his bachelor's degree from Seattle Pacific University in 1976.

While in graduate school at UC Berkeley, Wall and his wife were studying linguistics with the intention afterwards of finding an unwritten language, perhaps in Africa, and creating a writing system for it. They would then use this new writing system to translate various texts into the language, among them the Bible. Due to health reasons these plans were cancelled, and they remained in the U.S., where Larry instead joined the NASA Jet Propulsion Laboratory after he finished graduate school.

Accomplishments

Wall is the author of the rn Usenet client and the nearly universally-used patch program. He has won the International Obfuscated C Code Contest twice and was the recipient of the first Free Software Foundation Award for the Advancement of Free Software in 1998.

Beyond his technical skills, Wall has a reputation for his wit and for his often sarcastic sense of humour, which he displays in the comments to his source code or on Usenet. For example: "We all agree on the necessity of compromise. We just can't agree on when it's necessary to compromise" and:

For example, it's been several decades now since a certain set of Bible translations came out, and you'll notice a pattern: the New English Bible, the New American Standard Bible, and the New International Version, to name a few. It's really funny. I suspect we'll still be calling them “new this” and “new that” a hundred years from now. Much like New College at Oxford. Do you know when New College was founded. Any guesses? New College was new in 1379.

Virtues of a programmer

In the second edition of ''Programming Perl'', Wall (along with coauthors Randal L. Schwartz and Tom Christiansen) outlined the ''Three Virtues of a Programmer'':

# Laziness - The quality that makes you go to great effort to reduce overall energy expenditure. It makes you write labor-saving programs that other people will find useful, and document what you wrote so you don't have to answer so many questions about it. Hence, the first great virtue of a programmer. Also hence, this book. See also impatience and hubris. # Impatience - The anger you feel when the computer is being lazy. This makes you write programs that don't just react to your needs, but actually anticipate them. Or at least pretend to. Hence, the second great virtue of a programmer. See also laziness and hubris. #Hubris - Excessive pride, the sort of thing Zeus zaps you for. Also the quality that makes you write (and maintain) programs that other people won't want to say bad things about. Hence, the third great virtue of a programmer. See also laziness and impatience.

See also

List of computer scientists

List of programmers

Perl

References

External links

Larry Wall's personal home page

Slightly Skeptical View on Larry Wall and Perl (Softpanorama Larry Wall's page)

Authoritative list of Larry Wall quotes

''Perl, the first Postmodern Language''

State of the Onion keynotes: 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Please note that as the State of the Onion speeches are often primarily based on visual humour, the transcripts may seem confusing or nonsensical.

Category:1954 births Category:Living people Category:Perl Category:American computer programmers Category:Free software programmers Category:Perl writers Category:Perl people Category:Programming language designers Category:Seattle Pacific University alumni Category:University of California, Berkeley alumni Category:American Christians Category:O'Reilly writers

ar:لاري وول ca:Larry Wall cs:Larry Wall de:Larry Wall et:Larry Wall es:Larry Wall fa:لری وال fr:Larry Wall id:Larry Wall it:Larry Wall he:לארי וול lt:Laris Volas ml:ലാറി വാൾ nl:Larry Wall ja:ラリー・ウォール no:Larry Wall pl:Larry Wall pt:Larry Wall ro:Larry Wall ru:Уолл, Ларри simple:Larry Wall sl:Larry Wall sr:Лари Вол sv:Larry Wall th:แลร์รี วอลล์ zh:拉里·沃尔

This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.

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