Questions tagged [java]

Java is a high-level object-oriented programming language. Use this tag when you're having problems using or understanding the language itself. This tag is frequently used alongside other tags for libraries and/or frameworks used by Java developers.

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.


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

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).

Very few computers can run Java programs directly. Before Java 9, users running Java programs were expected to have the JRE (Java Runtime Environment) installed on their system. Modern Java programs intended to run directly on client computers now ship with their own installers.


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

Version Code Name Release Date
Java SE 19 JSR 394 September 20, 2022
Java SE 18 JSR 393 March 22, 2022
Java SE 17 JSR 392 September 14, 2021
Java SE 16 JSR 391 March 16, 2021
Java SE 15 JSR 390 September 15, 2020
Java SE 14 JSR 389 March 17, 2020
Java SE 13 JSR 388 September 17, 2019
Java SE 12 JSR 386 March 19, 2019
Java SE 11 JSR 384 September 25, 2018
Java SE 10 JSR 383 March 20, 2018
Java SE 9 JSR 376 September 21, 2017
Java SE 8 (1.8) JSR 337 March 18, 2014
Java SE 7 (1.7) Dolphin July 28, 2011
Java SE 6 (1.6) Mustang December 11, 2006
J2SE 5.0 (1.5) Tiger September 29, 2004
J2SE 1.4 Merlin February 13, 2002
J2SE 1.3 Kestrel May 8, 2000
J2SE 1.2 Playground December 4, 1998
JDK 1.1 February 19, 1997
JDK 1.0 January 23, 1996
JDK Beta 1995

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

Latest Stable Versions:

Version Release Date
Java Standard Edition 19 (19) September 20, 2022
Java Standard Edition 18 ( August 18, 2022
Java Standard Edition 17 ( August 18, 2022
Java Standard Edition 16 (16.0.2) July 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 ( August 18, 2022
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 341 (1.8.0_341) July 19, 2022
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:

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



String, StringBuilder and toString:

equals and hashCode:

Java Platform SE API:


Classes and objects:

Arithmetic and conversions:


Thread and multithreading:

Interacting with the operating system:

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


1866104 questions
27 answers

Why is processing a sorted array faster than processing an unsorted array?

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Is Java "pass-by-reference" or "pass-by-value"?

I always thought Java uses pass-by-reference. However, I've seen a blog post that claims that Java uses pass-by-value. I don't think I understand the distinction they're making. What is the explanation?
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Proper use cases for Android UserManager.isUserAGoat()?

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Until today, I thought that for example: i += j; Was just a shortcut for: i = i + j; But if we try this: int i = 5; long j = 8; Then i = i + j; will not compile but i += j; will compile fine. Does it mean that in fact i += j; is a shortcut for…
18 answers

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Iterate through a HashMap

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How can I create a memory leak in Java?

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What is the difference between public, protected, package-private and private in Java?

In Java, are there clear rules on when to use each of access modifiers, namely the default (package private), public, protected and private, while making class and interface and dealing with inheritance?
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