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Java (programming language)

java programming language tutorial, java programming language pdf
Java is a general-purpose computer programming language that is concurrent, class-based, object-oriented, and specifically designed to have as few implementation dependencies as possible It is intended to let application developers "write once, run anywhere" WORA, meaning that compiled Java code can run on all platforms that support Java without the need for recompilation Java applications are typically compiled to bytecode that can run on any Java virtual machine JVM regardless of computer architecture As of 2016, Java is one of the most popular programming languages in use, particularly for client-server web applications, with a reported 9 million developers Java was originally developed by James Gosling at Sun Microsystems which has since been acquired by Oracle Corporation and released in 1995 as a core component of Sun Microsystems' Java platform The language derives much of its syntax from C and C++, but it has fewer low-level facilities than either of them

The original and reference implementation Java compilers, virtual machines, and class libraries were originally released by Sun under proprietary licences 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 bytecode compiler, GNU Classpath standard libraries, and IcedTea-Web browser plugin for applets

The latest version is Java 8, which is the only version currently supported for free by Oracle, although earlier versions are supported both by Oracle and other companies on a commercial basis

Contents

  • 1 History
    • 11 Principles
    • 12 Versions
  • 2 Practices
    • 21 Java platform
      • 211 Implementations
      • 212 Performance
    • 22 Automatic memory management
  • 3 Syntax
  • 4 Examples
    • 41 "Hello, world!" program
    • 42 Comprehensive example
  • 5 Special classes
    • 51 Applet
    • 52 Servlet
    • 53 JavaServer Pages
    • 54 Swing application
    • 55 Generics
  • 6 Criticism
  • 7 Use outside of the Java platform
    • 71 Google
  • 8 Class libraries
  • 9 Documentation
  • 10 Editions
  • 11 See also
    • 111 Comparison of Java with other languages
  • 12 Notes
  • 13 References
  • 14 External links

History

See also: Java software platform § History Duke, the Java mascot James Gosling, the creator of Java 2008 The TIOBE programming language popularity index graph from 2002 to 2015 Over the course of a decade Java blue and C black competing for the top position

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 Later the project went by the name Green and was finally renamed Java, from Java coffee Gosling designed Java with a C/C++-style syntax that system and application programmers would find familiar

Sun Microsystems released the first public implementation as Java 10 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, while mostly outside of browsers, that wasn't the original plan In January 2016, Oracle announced that Java runtime environments based on JDK 9 will discontinue the browser plugin The Java 10 compiler was re-written in Java by Arthur van Hoff to comply strictly with the Java 10 language specification With the advent of Java 2 released initially as J2SE 12 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 EE, Java 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 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

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

Sun's vice-president Rich Green said that Sun's ideal role with regard to Java was as an "evangelist" 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" This did not prevent Oracle from filing a lawsuit against Google shortly after that for using Java inside the Android SDK see Google section below Java software runs on everything from laptops to data centers, game consoles to scientific supercomputers On April 2, 2010, James Gosling resigned from Oracle

Principles

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

  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 "interpreted, threaded, and dynamic"

Versions

Main article: Java version history

As of 2015, only Java 8 is supported "publicly" Major release versions of Java, along with their release dates:

  • JDK 10 January 21, 1996
  • JDK 11 February 19, 1997
  • J2SE 12 December 8, 1998
  • J2SE 13 May 8, 2000
  • J2SE 14 February 6, 2002
  • J2SE 50 September 30, 2004
  • Java SE 6 December 11, 2006
  • Java SE 7 July 28, 2011
  • Java SE 8 March 18, 2014

Practices

Java platform

Main articles: Java software platform and Java virtual machine Java Control Panel, version 7

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 runtime 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 own 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 makes interpreted programs almost always run more slowly than native executables However, just-in-time JIT compilers that compile bytecodes 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 for it, which translates the Java bytecode into the platform's machine language

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 currently "publicly" supported, Mac OS X, Linux and Solaris Because Java lacks any formal standardization recognized by Ecma International, ISO/IEC, ANSI, or other third-party standards organization, 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 compiler, Javadoc, Jar, and a debugger

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 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

Performance

Main article: Java 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 11, 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 the default for Sun's JVM in 2000 With Java 15, the performance was improved with the addition of the javautilconcurrent package, including Lock free implementations of the ConcurrentMaps and other multi-core collections, and it was improved further Java 16

Some platforms offer direct hardware support for Java; there are microcontrollers that can run Java in hardware instead of a software Java virtual machine, and ARM based processors can have hardware support for executing Java bytecode through their Jazelle option while its support is mostly 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 nonexistent object are called, a "null pointer exception" is thrown

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, ie, 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 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 By default, HotSpot uses the parallel scavenge 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 Concurrent Mark-Sweep CMS garbage collector is sufficient Oracle aims to replace CMS with the Garbage-First collector G1

Syntax

Main article: Java syntax

The syntax of Java is largely influenced by 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 classes, and every data item is an object, with the exception of the primitive data types, ie integers, floating-point numbers, boolean values, and characters, which are not objects for performance reasons Java reuses some popular aspects of C++ such as printf method

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

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

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 / package fibsandlies; import javautilHashMap; / 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 / public class FibCalculator extends Fibonacci implements Calculator / 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 fibonacciint fibIndex else

Examples

"Hello, world!" program

The traditional "Hello, world!" program can be written in Java as:

class HelloWorldApp

Source files must be named after the public class they contain, appending the suffix java, for example, HelloWorldAppjava It must first be compiled into bytecode, using a Java compiler, producing a file named HelloWorldAppclass 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 other than public access and any number of public inner classes When the source file contains multiple classes, make one class "public" 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 and protected

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 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 Systemexit 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 mainString 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 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 mainString 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 printlnString which also appends a new line to the passed string

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

Comprehensive example

// OddEvenjava import javaxswingJOptionPane; public class OddEven / This is the main method It gets called when this class is run through a Java interpreter @param args command line arguments unused / public static void mainfinal String args public void showDialog catch final NumberFormatException e / 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 usersAssuming it's open / private void calculate else
  • The import statement imports the JOptionPane class from the javaxswing package
  • The OddEven class declares a single private field of type int named userInput Every instance of the OddEven class has its own copy of the userInput field The private declaration means that no other class can access read or write the userInput field
  • OddEven is a public constructor Constructors have the same name as the enclosing class they are declared in, and unlike a method, have no return type A constructor is used to initialize an object that is a newly created instance of the class
  • The calculate method is declared without the static keyword This means that the method is invoked using a specific instance of the OddEven class The reference used to invoke the method is passed as an undeclared parameter of type OddEven named this The method tests the expression userInput % 2 == 0 using the if keyword to see if the remainder of dividing the userInput field belonging to the instance of the class by two is zero If this expression is true, then it prints Even; if this expression is false it prints Odd The calculate method can be equivalently accessed as thiscalculate and the userInput field can be equivalently accessed as thisuserInput, which both explicitly use the undeclared this parameter
  • OddEven number = new OddEven; declares a local object reference variable in the main method named number This variable can hold a reference to an object of type OddEven The declaration initializes number by first creating an instance of the OddEven class, using the new keyword and the OddEven constructor, and then assigning this instance to the variable
  • The statement numbershowDialog; calls the calculate method The instance of OddEven object referenced by the number local variable is used to invoke the method and passed as the undeclared this parameter to the calculate method
  • userInput = IntegerparseIntJOptionPaneshowInputDialog"Please Enter A Number"; is a statement that converts the type of String to the primitive data type int by using a utility function in the primitive wrapper class Integer

Special classes

Applet

Main article: Java applet

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

// Hellojava import javaxswingJApplet; import javaawtGraphics; public class Hello extends JApplet

The import statements direct the Java compiler to include the javaxswingJApplet and javaawtGraphics classes in the compilation The import statement allows these classes to be referenced in the source code using the simple class name ie JApplet instead of the fully qualified class name FQCN, ie javaxswingJApplet

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 paintComponentGraphics method additionally indicated with the annotation, supported as of JDK 15, Override inherited from the Container 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 drawStringString, int, int method to display the "Hello, world!" string at a pixel offset of 65, 95 from the upper-left corner in the applet's display

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 401//EN" "http://wwww3org/TR/html4/strictdtd"> <!-- Hellohtml --> <html> <head> <title>Hello World Applet</title> </head> <body> <applet code="Helloclass" width="200" height="200"> </applet> </body> </html>

An applet is placed in an HTML document using the <applet> 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 AppletContext 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

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 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

// Hellojava import javaio; import javaxservlet; public class Hello extends GenericServlet finally

The import statements direct the Java compiler to include all the public classes and interfaces from the javaio and javaxservlet packages in the compilation Packages make Java well suited for large scale applications

The Hello class extends the GenericServlet 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 serviceServletRequest, ServletResponse method defined by the Servlet interface to provide the code for the service request handler The service method is passed: a ServletRequest object that contains the request from the client and a ServletResponse object used to create the response returned to the client The service method declares that it throws the exceptions ServletException and IOException if a problem prevents it from responding to the request

The setContentTypeString method in the response object is called to set the MIME content type of the returned data to "text/html" The getWriter method in the response returns a PrintWriter object that is used to write the data that is sent to the client The printlnString method is called to write the "Hello, world!" string to the response and then the close 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

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

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 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:

// Hellojava Java SE 5 import javaxswing; public class Hello extends JFrame public static void mainfinal String args

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

The Hello class extends the JFrame 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 setDefaultCloseOperationint method inherited from JFrame to set the default operation when the close control on the title bar is selected to WindowConstantsEXIT_ON_CLOSE – this causes the JFrame to be disposed of when the frame is closed as opposed to merely hidden, which allows the Java virtual machine to exit and the program to terminate Next, a JLabel is created for the string "Hello, world!" and the addComponent method inherited from the Container superclass is called to add the label to the frame The pack method inherited from the Window superclass is called to size the window and lay out its contents

The main method is called by the Java virtual machine when the program starts It instantiates a new Hello frame and causes it to be displayed by calling the setVisibleboolean method inherited from the Component 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

Main article: Generics in Java

In 2004, generics were added to the Java language, as part of J2SE 50 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 converted to compile-time errors, a characteristic known as type safety

Criticism

Main article: Criticism of Java

Criticisms directed at Java include the implementation of generics, speed, the handling of unsigned numbers, the implementation of floating-point arithmetic, and a history of security vulnerabilities in the primary Java VM implementation HotSpot

Use outside of 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 It supports Java 6 and some Java 7 features, offering a compatible implementation of a significant part of the standard library Apache Harmony 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

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

Google

See also: Oracle America, Inc v Google, Inc

The Java language is a key pillar in Android, an open source mobile operating system Although Android, built on the Linux kernel, was written largely in C, the Android SDK uses the Java language as the basis for Android applications However, Android does not use the standard Java virtual machine, instead using Java bytecode as an intermediate step which is transformed into Dalvik bytecode Depending on the Android version, this is then either interpreted by the Dalvik virtual machine, or compiled into native code by the Android Runtime

Android also does not provide the full Java SE standard library, although the Android class library does include an independent implementation of a large subset of it This 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 District Judge William Haskell Alsup ruled on May 31, 2012, that APIs cannot be copyrighted, but this was reversed by the United States Court of Appeals for the Federal Circuit in May 2014

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 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 The class library contains features such as:

  • The core libraries, which include:
    • IO/NIO
    • Networking
    • Reflection
    • Concurrency
    • Generics
    • Scripting/Compiler
    • Functional Programming Lambda, Streaming
    • 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
    • JavaFX
  • A platform dependent implementation of the Java virtual machine that is the means by which the bytecodes 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

Main article: Javadoc

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, ie the delimiters are / and /, whereas the normal multi-line comments in Java are set off with the delimiters / and /

Editions

See also: Free Java implementations § Class library Java editions