Java is a high-level, platform-independent, object-oriented, functional programming language and runtime environment.

The Java language derives much of its syntax from C and C++, but its object model is simpler than that of the latter and it has fewer low-level facilities. Java applications are typically compiled to bytecode (called class files) that can be executed by a JVM (Java Virtual Machine), independent of computer architecture. The JVM often further compiles code to native machine code to optimize performance.

The JVM manages memory with the help of a garbage collector (see also garbage-collection) to handle object removal from memory when objects are no longer in use. Java's typing discipline is static, strong, safe, nominative, and manifest. Java supports features such as reflection and interfacing with C and C++ via the JNI (Java Native Interface).

Java is designed to have as few implementation dependencies as possible, intended to allow application developers to write once, run anywhere, or sometimes write once, run everywhere (code that executes on one platform does not need to be recompiled to run on another). Java was originally developed by James Gosling at Sun Microsystems (which fully merged with Oracle Corporation on January 27th, 2010) and was released in 1995 as a core component of Sun Microsystems' Java platform. Java was started as a project called "Oak" by James Gosling in June 1991.

The Java platform is the name given by Sun (now Oracle) to computing systems that have installed tools for developing and running Java programs. The platform features a wide variety of tools that can help developers work efficiently with the Java programming language.

To get started, you download a Java Development Kit (JDK), which lets you both develop and run java applications.

Background

The main reference implementation of Java is open source (the OpenJDK) and is supported by major companies including Oracle, Apple, SAP, and IBM.

Very few computers can run Java programs directly. Java software often runs on servers. Java apps intended to run directly on client computers should ship with their own installers. (NB: Before java9, you asked end-users to install a so-called JRE; however, this concept has been deprecated).

Java is compiled into bytecode, which is then compiled by the JVM into native machine code. The compilation is done just-in-time (JIT). This was initially viewed as a performance hit, but JVM and JIT compilation improvements have made this less of a concern. In some cases, the JVM may even be faster than native code compiled to target an older version of a processor for backward compatibility reasons. Since Java 9, it can be compiled ahead-of-time (AOT).

Versions

Notable Java versions, code names, and release dates include:

VersionCode NameRelease Date
Java SE 16JSR 391March 16, 2021
Java SE 15JSR 390September 15, 2020
Java SE 14JSR 389March 17, 2020
Java SE 13JSR 388September 17, 2019
Java SE 12JSR 386March 19, 2019
Java SE 11JSR 384September 25, 2018
Java SE 10JSR 383March 20, 2018
Java SE 9JSR 376September 21, 2017
Java SE 8 (1.8)JSR 337March 18, 2014
Java SE 7 (1.7)DolphinJuly 28, 2011
Java SE 6 (1.6)MustangDecember 11, 2006
J2SE 5.0 (1.5)TigerSeptember 29, 2004
J2SE 1.4MerlinFebruary 13, 2002
J2SE 1.3KestrelMay 8, 2000
J2SE 1.2PlaygroundDecember 4, 1998
JDK 1.1February 19, 1997
JDK 1.0January 23, 1996
JDK Beta1995

Since Java SE 10, new versions will be released every six months.

Latest Stable Versions:

VersionRelease Date
Java Standard Edition 16 (16.0.1)April 20, 2021
Java Standard Edition 15 (15.0.2)January 19, 2021
Java Standard Edition 14 (14.0.2)July 14, 2020
Java Standard Edition 13 (13.0.2)January 14, 2020
Java Standard Edition 12 (12.0.2)July 16, 2019
Java Standard Edition 11 (11.0.11)April 20, 2021
Java Standard Edition 10 (10.0.2)July 17, 2018
Java Standard Edition 9 (9.0.4)January 16, 2018
Java Standard Edition 8 Update 291 (1.8.0_291)April 20, 2021
Java Standard Edition 7 Update 80 (1.7.0_80)April 14, 2015

For more code names and release dates, visit Java SE Code Names. To see release notes for each version of the JDK, visit the Wikipedia article on Java version history.

To get a Java JDK so you can develop (or run) java code on your machine, you need a java installer package supplier. Java is open source, but a supplier will take care of building the java source code into a binary, wrapping this into an installer, and maintaining this version on your machine (e.g. with security updates).

Java comes in LTS (Long-Term-Support) and non-LTS versions. Each supplier chooses how to deal with LTS versions. Some (Oracle OpenJDK) have the same short support window for all releases, LTS or not. Some (Amazon Corretto) do not bother to release non-LTS versions at all. Most suppliers release all versions that will support LTS versions for far longer.

The LTS versions are- Java 8, 11, and 17.

The major suppliers are:

  • AdoptOpenJDK, also known as Adoptium - free, LTS versions and non-LTS versions, LTS versions are supported a long time. Recommended.
  • Oracle OpenJDK - Note that these are only supported for 6 months, even the so-called LTS (Long Term Support) releases. You will need to update as java updates.
  • Oracle JavaSE - licensed for those who want commercial support. LTS and non-LTS versions, LTS versions are supported for a long time. A free but license-wise very restricted test version is available.
  • Amazon Coretto - free, maintained by Amazon, optimized for AWS, LTS versions only.
  • Many more commercial offerings.

The End of Public Updates (Formerly called End Of Life and also referred to as EoPU) dates for the freely available distribution from Oracle are:

VersionEoPU Date
Java SE 16September 2021 for OpenJDK
Java SE 15March 2021 for OpenJDK
Java SE 14September 2020 for OpenJDK
Java SE 13March 2020 for OpenJDK
Java SE 12September 2019 for OpenJDK
Java SE 11At least September 2022 for AdoptOpenJDK
Java SE 10September 2018
Java SE 9March 2018
Java SE 8January 2019 (commercial use)
Java SE 7Apr 2015
Java SE 6Feb 2013
J2SE 5.0Oct 2009
J2SE 1.4Oct 2008

Initial help

New to Java or need help to get your first Java program running? See the Oracle Java Tutorials section on Getting Started.

Before asking a question, please search to see if it has been asked before (we have many duplicates, some are listed below under Frequently Asked Questions), and read Writing the Perfect Question to learn how to get Jon Skeet to answer your question.

Naming conventions

Java programs should adhere to the following naming conventions to increase readability and decrease the chances of accidental errors. By following these naming conventions, you will make it easier for others to understand your code and help you.

  • Type names (classes, interfaces, enums, etc.) should begin with a capital letter and capitalize the first letter of each subsequent word. Examples include: String, ThreadLocal, and NullPointerException. This is sometimes known as PascalCase.
  • Method and field names should be camelCased; that is, they should begin with a lowercase letter and capitalize the first letter of each subsequent word. Examples: indexOf, printStackTrace, interrupt.
  • Constant expression names (static final immutable objects) should be written in ALL_CAPS_SNAKE_CASE, with underscores separating each word. Examples: YELLOW, DO_NOTHING_ON_CLOSE. This also applies to the values of an Enum class. However, static final references to non-immutable objects should be camelCased.

Hello World - Your first program

Code of a typical Hello World program:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Compilation and invocation of Hello World program:

javac -d . HelloWorld.java
java -cp . HelloWorld

Java source code is compiled to an intermediate form (bytecode instructions for the Java Virtual Machine) which can be executed with the java command later on.

More information:

Useful IDEs for Java

Beginners' resources

Online Compilers

Day-to-day updated resources

Advanced resources

Java frameworks, libraries, and software

Java programming books and resources

Frequently Asked Questions

People often ask about the following Java topics:

General:

Classpath:

String, StringBuilder and toString:

equals and hashCode:

Java Platform SE API:

Generics:

Classes and objects:

Arithmetic and conversions:

Debugging:

Thread and multithreading:

Interacting with the operating system:

(Editors, please only list questions which actually are frequently asked.)

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