Java version history

The first version was released on January 23, 1996.[24][25] The first stable version, JDK 1.0.2, is called Java 1.[25]

Major additions in the release on February 19, 1997 included:[26]

• an extensive retooling of the AWT event model
• inner classes added to the language
• JavaBeans
• JDBC
• RMI and serialization
• reflection which supported Introspection only, no modification at runtime was possible. (The ability to modify objects reflectively was added in J2SE 1.2, by introducing the AccessibleObject class and its subclasses such as the Field class.)
• JIT (Just In Time) compiler on Microsoft Windows platforms, produced for JavaSoft by Symantec
• Internationalization and Unicode support originating from Taligent[27]

The release on December 8, 1998 and subsequent releases through J2SE 5.0 were rebranded retrospectively Java 2 and the version name "J2SE" (Java 2 Platform, Standard Edition) replaced JDK to distinguish the base platform from J2EE (Java 2 Platform, Enterprise Edition) and J2ME (Java 2 Platform, Micro Edition). This was a very significant release of Java as it tripled the size of the Java platform to 1520 classes in 59 packages. Major additions included:[28]

• strictfp keyword (by JVM 17 an obsolete keyword, shouldn't be used in new code)
• the Swing graphical API was integrated into the core classes
• Sun's JVM was equipped with a JIT compiler for the first time
• Java plug-in
• Java IDL, an IDL implementation for CORBA interoperability
• Collections framework

The most notable changes in the May 8, 2000 release were:[29][30]

• HotSpot JVM included (the HotSpot JVM was first released in April 1999 for the J2SE 1.2 JVM)
• RMI was modified to support optional compatibility with CORBA
• Java Naming and Directory Interface (JNDI) included in core libraries (previously available as an extension)
• Java Platform Debugger Architecture (JPDA)
• JavaSound
• Synthetic proxy classes

Java 1.3 is the last release of Java to officially support Microsoft Windows 95.[31]

The February 6, 2002 release was the first release of the Java platform developed under the Java Community Process as JSR 59. Major changes included:[32][33]

• Language changes
  • assert keyword (specified in JSR 41)
• Library improvements
  • Regular expressions modeled after Perl regular expressions
  • Exception chaining allows an exception to encapsulate original lower-level exception
  • Internet Protocol version 6 (IPv6) support
  • Non-blocking I/O (named NIO) (specified in JSR 51)
  • Logging API (specified in JSR 47)
  • Image I/O API for reading and writing images in formats like JPEG and PNG
  • Integrated XML parser and XSLT processor (JAXP) (specified in JSR 5 and JSR 63)
  • Integrated security and cryptography extensions (JCE, JSSE, JAAS)
  • Java Web Start included (Java Web Start was first released in March 2001 for J2SE 1.3) (specified in JSR 56)
  • Preferences API (java.util.prefs)

Public support and security updates for Java 1.4 ended in October 2008. Paid security updates for Oracle customers ended in February 2013.[34]

The release on September 30, 2004 was originally numbered 1.5, which is still used as the internal version number. The number was changed to "better reflect the level of maturity, stability, scalability and security of the J2SE".[35] This version was developed under JSR 176.

Java SE 5 entered its end-of-public-updates period on April 8, 2008; updates are no longer available to the public as of November 3, 2009. Updates were available to paid Oracle customers until May 2015.[3]

Tiger added a number of significant new language features:[36][37]

• Generics: provides compile-time (static) type safety for collections and eliminates the need for most typecasts (type conversion) (specified by JSR 14)
• Metadata: also called annotations; allows language constructs such as classes and methods to be tagged with additional data, which can then be processed by metadata-aware utilities (specified by JSR 175)
• Autoboxing/unboxing: automatic conversions between primitive types (such as int) and primitive wrapper classes (such as Integer) (specified by JSR 201)
• Enumerations: the enum keyword creates a typesafe, ordered list of values (such as Day.MONDAY, Day.TUESDAY, etc.); previously this could only be achieved by non-typesafe constant integers or manually constructed classes (typesafe enum pattern) (specified by JSR 201)
• Varargs: the last parameter of a method can now be declared using a type name followed by three dots (e.g. void drawtext(String... lines)); in the calling code any number of parameters of that type can be used and they are then placed in an array to be passed to the method, or alternatively the calling code can pass an array of that type
• Enhanced for each loop: the for loop syntax is extended with special syntax for iterating over each member of either an array or any Iterable, such as the standard Collection classes (specified by JSR 201)
• Improved semantics of execution for multi-threaded Java programs; the new Java memory model addresses issues of complexity, effectiveness, and performance of previous specifications[38]
• Static imports

There were also the following improvements to the standard libraries:

• Automatic stub generation for RMI objects
• Swing: New skinnable look and feel, called synth
• The concurrency utilities in package java.util.concurrent[39]
• Scanner class for parsing data from various input streams and buffers

Java 5 is the last release of Java to officially support Microsoft Windows 98 and Windows ME,[40] while Windows Vista was the newest version of Windows that Java SE 5 was supported on prior to Java 5 going end-of-life in October of 2009.[34]

Java 5 Update 5 (1.5.0_05) is the last release of Java to work on Windows 95 (with Internet Explorer 5.5 installed) and Windows NT 4.0.[41]

Java 5 was first available on Apple Mac OS X 10.4 (Tiger)[42] and was the default version of Java installed on Apple Mac OS X 10.5 (Leopard).

Public support and security updates for Java 1.5 ended in November 2009. Paid security updates for Oracle customers ended in April 2015.

As of the version released on December 11, 2006, Sun replaced the name "J2SE" with Java SE and dropped the ".0" from the version number.[44] Internal numbering for developers remains 1.6.0.[45]

This version was developed under JSR 270.

During the development phase, new builds including enhancements and bug fixes were released approximately weekly. Beta versions were released in February and June 2006, leading up to a final release that occurred on December 11, 2006.

Major changes included in this version:[46][47]

• Support for older Win9x versions dropped; unofficially, Java 6 Update 7 was the last release of Java shown to work on these versions of Windows. This is believed to be due to the major changes in Update 10.
• Scripting Language Support (JSR 223): Generic API for tight integration with scripting languages, and built-in Mozilla JavaScript Rhino integration.
• Dramatic performance improvements for the core platform,[48][49] and Swing.
• Improved Web Service support through JAX-WS (JSR 224).
• JDBC 4.0 support (JSR 221).
• Java Compiler API (JSR 199): an API allowing a Java program to select and invoke a Java Compiler programmatically.
• Upgrade of JAXB to version 2.0: Including integration of a StAX parser.
• Support for pluggable annotations (JSR 269).[50]
• Many GUI improvements, such as integration of SwingWorker in the API, table sorting and filtering, and true Swing double-buffering (eliminating the gray-area effect).
• JVM improvements include: synchronization and compiler performance optimizations, new algorithms and upgrades to existing garbage collection algorithms, and application start-up performance.

Java 6 can be installed to Mac OS X 10.5 (Leopard) running on 64-bit (Core 2 Duo and higher) processor machines.[51] Java 6 is also supported by both 32-bit and 64-bit machines running Mac OS X 10.6 (Snow Leopard).

Java 6 reached the end of its supported life in February 2013, at which time all public updates, including security updates, were scheduled to be stopped.[52][53] Oracle released two more updates to Java 6 in March and April 2013, which patched some security vulnerabilities.[54][55]

Java 7 is a major update that was launched on July 7, 2011[57] and was made available for developers on July 28, 2011.[58] The development period was organized into thirteen milestones; on June 6, 2011, the last of the thirteen milestones was finished.[58][59] On average, 8 builds (which generally included enhancements and bug fixes) were released per milestone. The feature list at the OpenJDK 7 project lists many of the changes.

Additions in Java 7 include:[60]

• JVM support for dynamic languages, with the new invokedynamic bytecode under JSR-292,[61] following the prototyping work currently done on the Multi Language Virtual Machine
• Compressed 64-bit pointers[62] (available in Java 6 with -XX:+UseCompressedOops)[63]
• These small language changes (grouped under a project named Coin):[64]

• Strings in switch[65]
• Automatic resource management in try-statement aka try-with-resources statement[66]
• Improved type inference for generic instance creation, aka the diamond operator <>[67]
• Simplified varargs method declaration[68]
• Binary integer literals[69]
• Allowing underscores in numeric literals[70]
• Catching multiple exception types and rethrowing exceptions with improved type checking[71]

• Concurrency utilities under JSR 166[72]
• New file I/O library (defined by JSR 203) adding support for multiple file systems, file metadata and symbolic links. The new packages are java.nio.file, java.nio.file.attribute and java.nio.file.spi[73][74]
• Timsort is used to sort collections and arrays of objects instead of merge sort
• Library-level support for elliptic curve cryptography algorithms
• An XRender pipeline for Java 2D, which improves handling of features specific to modern GPUs
• New platform APIs for the graphics features originally implemented in version 6u10 as unsupported APIs[75]
• Enhanced library-level support for new network protocols, including SCTP and Sockets Direct Protocol
• Upstream updates to XML and Unicode
• Java deployment rule sets[76]

Lambda (Java's implementation of lambda functions), Jigsaw (Java's implementation of modules), and part of Coin were dropped from Java 7, and released as part of Java 8 (except for Jigsaw, which was released in Java 9).[77][78]

Java 7 was the default version to download on java.com from April 2012 until Java 8 was released.[79]

Java 8 was released on March 18, 2014,[83][84] and included some features that were planned for Java 7 but later deferred.[85]

Work on features was organized in terms of JDK Enhancement Proposals (JEPs).[86]

• JSR 335, JEP 126: Language-level support for lambda expressions (officially, lambda expressions; unofficially, closures) under Project Lambda[87] and default methods (virtual extension methods)[88][89][90] which can be used to add methods to interfaces without breaking existing implementations. There was an ongoing debate in the Java community on whether to add support for lambda expressions.[91][92] Sun later declared that lambda expressions would be included in Java and asked for community input to refine the feature.[93] Supporting lambda expressions also enables functional-style operations on streams of elements, such as MapReduce-inspired transformations on collections. Default methods can be used by an author of an API to add new methods to an interface without breaking the old code using it. Although it was not their primary intent,[88] default methods can also be used for multiple inheritance of behavior (but not state).

• JEP 174: Project Nashorn, a JavaScript runtime which can run JavaScript code embedded within applications
• JEP 104: Annotation on Java types
• Unsigned integer arithmetic[94]
• JEP 120: Repeating annotations
• JEP 150: Date and time API
• JEP 178: Statically-linked JNI libraries
• JEP 153: Launch JavaFX applications (direct launching of JavaFX application JARs)
• JEP 122: Remove the permanent generation

Java 8 is not supported on Windows XP[95] but as of JDK 8 update 25, it can still be installed and run under Windows XP.[96] Previous updates of JDK 8 could be run under XP by downloading archived zip format file and unzipping it for the executable.The last version of Java 8 could run on XP is update 251.But its components compatibility starts to break on unsupported OS in early build during Java 8 updates development.

From October 2014, Java 8 was the default version to download (and then again the download replacing Java 9) from the official website.[97] "Oracle will continue to provide Public Updates and auto updates of Java SE 8, Indefinitely for Personal Users".[4]

Java SE 9 was made available on September 21, 2017,[98] due to controversial acceptance of the current implementation of Project Jigsaw by Java Executive Committee,[99] which led Oracle to fix some open issues and concerns, and to refine some critical technical questions. In the last days of June 2017, Java Community Process expressed nearly unanimous consensus on the proposed Module System scheme.[100]

• JSR 376: Modularization of the JDK under Project Jigsaw (Java Platform Module System)[78]
• JavaDB was removed from JDK[101]
• JEP 193: Variable handles, define a standard means to invoke the equivalents of various java.util.concurrent.atomic and sun.misc.Unsafe operations
• JEP 213: Milling Project Coin, allow @SafeVarargs on private instance methods; Allow effectively-final variables to be used as resources in the try-with-resources statement; Allow diamond with anonymous classes if the argument type of the inferred type is denotable; Complete the removal, begun in Java SE 8, of underscore from the set of legal identifier names; Support for private methods in interfaces
• JEP 222: jshell: The Java Shell (Read-Eval-Print Loop): JShell is a REPL command-line interface for the Java language.[102]
• JEP 254: Compact Strings
• JEP 263: HiDPI graphics: automatic scaling and sizing
• JEP 266: More concurrency updates, it includes a Java implementation of Reactive Streams,[103] including a new Flow class[104] that included the interfaces previously provided by Reactive Streams[105]
• JEP 268: XML catalogs
• JEP 282: jlink: The Java Linker, create a tool that can assemble and optimize a set of modules and their dependencies into a custom run-time image. It effectively allows to produce a fully usable executable including the JVM to run it
• JEP 295: Ahead-of-Time Compilation, ahead-of-time compilation provided by GraalVM

The first Java 9 release candidate was released on August 9, 2017.[106] The first stable release of Java 9 was on September 21, 2017.[107]

OpenJDK 10 was released on March 20, 2018, with twelve new features confirmed.[113] Among these features were:

• JEP 286: Local-Variable Type Inference
• JEP 296: Consolidate the JDK Forest into a Single Repository
• JEP 304: Garbage-Collector Interface
• JEP 307: Parallel Full GC for G1
• JEP 310: Application Class-Data Sharing
• JEP 312: Thread-Local Handshakes
• JEP 313: Remove the Native-Header Generation Tool (javah)
• JEP 314: Additional Unicode Language-Tag Extensions
• JEP 316: Heap Allocation on Alternative Memory Devices
• JEP 317: Experimental Java-Based JIT Compiler
• JEP 319: Root Certificates
• JEP 322: Time-Based Release Versioning

The first of these JEP 286 Local-Variable Type Inference, allows the var keyword to be used for local variables with the actual type calculated by the compiler. So we can do:

var list = new ArrayList<String>(); // infers ArrayList<String>
var stream = list.stream();         // infers Stream<String>

JDK 11 was released on September 25, 2018 and the version is currently open for bug fixes. It offers LTS, or Long-Term Support. Among others, Java 11 includes a number of new features, such as:[114]

• JEP 181: Nest-Based Access Control
• JEP 309: Dynamic Class-File Constants
• JEP 315: Improve Aarch64 Intrinsics
• JEP 318: Epsilon: A No-Op Garbage Collector
• JEP 320: Remove the Java EE and CORBA Modules
• JEP 321: HTTP Client (Standard)
• JEP 323: Local-Variable Syntax for Lambda Parameters
• JEP 324: Key Agreement with Curve25519 and Curve448
• JEP 327: Unicode 10
• JEP 328: Flight Recorder
• JEP 329: ChaCha20 and Poly1305 Cryptographic Algorithms
• JEP 330: Launch Single-File Source-Code Programs
• JEP 331: Low-Overhead Heap Profiling
• JEP 332: Transport Layer Security (TLS) 1.3
• JEP 333: ZGC: A Scalable Low-Latency Garbage Collector (Experimental)
• JEP 335: Deprecate the Nashorn JavaScript Engine
• JEP 336: Deprecate the Pack200 Tools and API

A number of features from previous releases were dropped; in particular, Java applets and Java Web Start are no longer available. JavaFX, Java EE and CORBA modules have been removed from JDK.[115]

JDK 12 was released on March 19, 2019. Among others, Java 12 includes a number of new features, such as:[116]

• JEP 189: Shenandoah: A Low-Pause-Time Garbage Collector (Experimental)
• JEP 230: Microbenchmark Suite
• JEP 325: Switch Expressions (Preview)
• JEP 334: JVM Constants API
• JEP 340: One AArch64 Port, Not Two
• JEP 341: Default CDS Archives
• JEP 344: Abortable Mixed Collections for G1
• JEP 346: Promptly Return Unused Committed Memory from G1

The preview feature JEP 325 extends the switch statement so it can also be used as an expression, and adds a new form of case label where the right hand side is an expression. No break statement is needed. For complex expressions a yield statement can be used. This becomes standard in Java SE 14.

int ndays = switch(month) {
    case JAN, MAR, MAY, JUL, AUG, OCT, DEC -> 31;
    case APR, JUN, SEP, NOV -> 30;
    case FEB -> {
        if (year % 400 == 0) yield 29;
        else if (year % 100 == 0) yield 28;
        else if (year % 4 == 0) yield 29;
        else yield 28; }
};

JDK 13 was released on September 17, 2019. Java 13 includes the following new features, as well as "hundreds of smaller enhancements and thousands of bug fixes".[117]

• JEP 350: Dynamic CDS Archives
• JEP 351: ZGC: Uncommit Unused Memory
• JEP 353: Reimplement the Legacy Socket API
• JEP 354: Switch Expressions (Preview)
• JEP 355: Text Blocks (Preview)

JEP 355 Text Blocks allows multiline string literals:

String html = """
              <html lang="en">
                  <body>
                      <p>Hello, world</p>
                  </body>
              </html>
              """;

JDK 14 was released on March 17, 2020. Java 14 includes the following new features, as well as "hundreds of smaller enhancements and thousands of bug fixes".[118]

• JEP 305: Pattern Matching for instanceof (Preview)
• JEP 343: Packaging Tool (Incubator)
• JEP 345: NUMA-Aware Memory Allocation for G1
• JEP 349: JFR Event Streaming
• JEP 352: Non-Volatile Mapped Byte Buffers
• JEP 358: Helpful NullPointerExceptions
• JEP 359: Records (Preview)
• JEP 361: Switch Expressions (Standard)
• JEP 362: Deprecate the Solaris and SPARC Ports
• JEP 363: Remove the Concurrent Mark Sweep (CMS) Garbage Collector
• JEP 364: ZGC on macOS
• JEP 365: ZGC on Windows
• JEP 366: Deprecate the ParallelScavenge + SerialOld GC Combination
• JEP 367: Remove the Pack200 Tools and API
• JEP 368: Text Blocks (Second Preview)
• JEP 370: Foreign-Memory Access API (Incubator)

JEP 305, Pattern Matching for instanceof simplifies the common case of an instanceof test being immediately followed by cast, replacing

if (obj instanceof String) {
    String s = (String) obj;
    System.out.println( s.length() );
}

with

if (obj instanceof String s) {
    System.out.println( s.length() );
}

JEP 359 Records allows easy creation of simple immutable Tuple-like classes.[119]

record Point(int x, int y) { }
Point p = new Point(3,4);
System.out.println( p.x() );

JDK 15 was released on September 15, 2020. Java 15 adds e.g. support for multi-line string literals (aka Text Blocks). The Shenandoah and Z garbage collectors (latter sometimes abbreviated ZGC) are now ready for use in production (i.e. no longer marked experimental). Support for Oracle's Solaris operating system (and SPARC CPUs) is dropped (while still available in e.g. Java 11). The Nashorn JavaScript Engine is removed. Also removed some root CA certificates.

• JEP 339: Edwards-Curve Digital Signature Algorithm (EdDSA)
• JEP 360: Sealed Classes (Preview)
• JEP 371: Hidden Classes
• JEP 372: Remove the Nashorn JavaScript Engine
• JEP 373: Reimplement the Legacy DatagramSocket API
• JEP 374: Disable and Deprecate Biased Locking
• JEP 375: Pattern Matching for instanceof (Second Preview)
• JEP 377: ZGC: A Scalable Low-Latency Garbage Collector
• JEP 378: Text Blocks
• JEP 379: Shenandoah: A Low-Pause-Time Garbage Collector
• JEP 381: Remove the Solaris and SPARC Ports
• JEP 383: Foreign-Memory Access API (Second Incubator)
• JEP 384: Records (Second Preview)
• JEP 385: Deprecate RMI Activation for Removal

JEP 360 Sealed Classes adds sealed classes and interfaces that restrict which other classes or interfaces may extend or implement them. Only those classes specified in a permits clause may extend the class or interface.

package com.example.geometry;

public abstract sealed class Shape
    permits Circle, Rectangle, Square {...}

Together with records, sealed classes are sum types. They work well with other recent features like records, switch expressions, and pattern matching for instance-of. They all form part of a system for "Pattern matching in Java" first discussed by Gavin Bierman and Brian Goetz, in September 2018.[120]

JDK 16 was released on March 16, 2021. Java 16 removes Ahead-of-Time compilation (and Graal JIT) options.[121] The Java implementation itself was and is still written in C++, while as of Java 16, more recent C++14 (but still not e.g. C++17 or C++20) is allowed. The code was also moved to GitHub, dropping Mercurial as the source control system.

• JEP 338: Vector API (Incubator)
• JEP 347: Enable C++14 Language Features
• JEP 357: Migrate from Mercurial to Git
• JEP 369: Migrate to GitHub
• JEP 376: ZGC: Concurrent Thread-Stack Processing
• JEP 380: Unix-Domain Socket Channels
• JEP 386: Alpine Linux Port – not yet stable
• JEP 387: Elastic Metaspace
• JEP 388: Windows/AArch64 Port
• JEP 389: Foreign Linker API (Incubator)
• JEP 390: Warnings for Value-Based Classes
• JEP 392: Packaging Tool
• JEP 393: Foreign-Memory Access API (Third Incubator)
• JEP 394: Pattern Matching for instanceof
• JEP 395: Records
• JEP 396: Strongly Encapsulate JDK Internals by Default
• JEP 397: Sealed Classes (Second Preview)

JDK 17 is the current long-term support (LTS) release since September 2021.[122] Java 17 is the 2nd long-term support (LTS) release since switching to the new 6-month release cadence (the first being Java 11).

• JEP 306: Restore Always-Strict Floating-Point Semantics
• JEP 356: Enhanced Pseudo-Random Number Generators
• JEP 382: New macOS Rendering Pipeline
• JEP 391: macOS/AArch64 Port
• JEP 398: Deprecate the Applet API for Removal
• JEP 403: Strongly Encapsulate JDK Internals
• JEP 406: Pattern Matching for switch (Preview)
• JEP 407: Remove RMI Activation
• JEP 409: Sealed Classes
• JEP 410: Remove the Experimental AOT and JIT Compiler
• JEP 411: Deprecate the Security Manager for Removal
• JEP 412: Foreign Function & Memory API (Incubator)
• JEP 414: Vector API (Second Incubator)
• JEP 415: Context-Specific Deserialization Filters

JEP 406 extends the pattern matching syntax used in instanceof operations to switch statements and expressions. It allows cases to be selected based on the type of the argument, null cases and refining patterns

Object o = ...;
return switch (o) {
        case null       -> "Null";
        case String s   -> String.format("String %s", s);
        case Long l     -> String.format("long %d", l);
        case Double d   -> String.format("double %f", d);
        case Integer i && i > 0                            // refining patterns
                        -> String.format("positive int %d", i);
        case Integer i && i == 0 
                        -> String.format("zero int %d", i);
        case Integer i && i < 0 
                        -> String.format("negative int %d", i);
        default         -> o.toString();
    };
};

JDK 18 was released on March 22, 2022.

• JEP 400: UTF-8 by Default
• JEP 408: Simple Web Server
• JEP 413: Code Snippets in Java API Documentation
• JEP 416: Reimplement Core Reflection with Method Handles
• JEP 417: Vector API (Third Incubator)
• JEP 418: Internet-Address Resolution SPI
• JEP 419: Foreign Function & Memory API (Second Incubator)
• JEP 420: Pattern Matching for switch (Second Preview)
• JEP 421: Deprecate Finalization for Removal

JDK 19 was released on 20 September 2022.[123]

• JEP 405: Record Patterns (Preview)
• JEP 422: Linux/RISC-V Port
• JEP 424: Foreign Function & Memory API (Preview)
• JEP 425: Virtual Threads (Preview)
• JEP 426: Vector API (Fourth Incubator)
• JEP 427: Pattern Matching for switch (Third Preview)
• JEP 428: Structured Concurrency (Incubator)

JEP 405 allows record patterns, extending the pattern matching capabilities of instanceof operators, and switch expressions, to include record patterns that explicitly refer to the components of the record.

record Rectangle(int x, int y, int w, int h) {}

int area(Object o) {
    if (o instanceof Rectangle(int x, int y, int w, int h)) {
        return w * h;
    }
    return 0;
}

Such patterns can include nested patterns, where the components of records are themselves records, allowing patterns to match more object graphs.

Java 20 was released on 21 March 2023.[124]

• JEP 429: Scoped Values (Incubator)
• JEP 432: Record Patterns (Second Preview)
• JEP 433: Pattern Matching for switch (Fourth Preview)
• JEP 434: Foreign Function & Memory API (Second Preview)
• JEP 436: Virtual Threads (Second Preview)
• JEP 437: Structured Concurrency (Second Incubator)
• JEP 438: Vector API (Fifth Incubator)

• Project Valhalla: Value types, objects without identity but with an efficient memory layout and leading to better results of escape analysis.
• Project Panama: Improved interoperability with native code, to enable Java source code to call functions and use data types from other languages, in a way that is easier and has better performance than today. Vector API (a portable and relatively low-level abstraction layer for SIMD programming) is also developed under Project Panama umbrella.
• Project Loom: Virtual threads, a lightweight user-mode scheduled alternative to standard OS managed threads. Virtual threads are mapped to OS threads in a many-to-many relationship, in contrast to the many-to-one relationship from the original green threads implementation in early versions of Java.

The officially supported Java platform, first developed at Sun and now stewarded by Oracle, is Java SE. Releases are based on the OpenJDK project, a free and open-source project with an open development model. Other Java implementations exist, however—in part due to Java's early history as proprietary software. In contrast, some implementations were created to offer some benefits over the standard implementation, often the result of some area of academic or corporate-sponsored research. Many Linux distributions include builds of OpenJDK through the IcedTea project started by Red Hat, which provides a more straightforward build and integration environment.

Visual J++ and the Microsoft Java Virtual Machine were created as incompatible implementations. After the Sun v. Microsoft lawsuit, Microsoft abandoned it and began work on the .NET platform. In 2021, Microsoft started distributing compatible "Microsoft Build of OpenJDK" for Java 11 first then also for Java 17. Their builds support not only Windows, but also Linux and macOS.

Other proprietary Java implementations are available, such as Azul's Zing. Azul offers certified open source OpenJDK builds under the Zulu moniker.

Prior to the release of OpenJDK, while Sun's implementation was still proprietary, the GNU Classpath project was created to provide a free and open-source implementation of the Java platform. Since the release of JDK 7, when OpenJDK became the official reference implementation, the original motivation for the GNU Classpath project almost completely disappeared, and its last release was in 2012.

The Apache Harmony project was started shortly before the release of OpenJDK. After Sun's initial source code release, the Harmony project continued, working to provide an implementation under a lax license, in contrast to the protective license chosen for OpenJDK. Google later developed Android and released it under a lax license. Android incorporated parts of the Harmony project, supplemented with Google's own Dalvik virtual machine and ART. Apache Harmony has since been retired, and Google has switched its Harmony components with equivalent ones from OpenJDK.

Both Jikes and Jikes RVM are open-source research projects that IBM developed.

Several other implementations exist that started as proprietary software but are now open source. IBM initially developed OpenJ9 as the proprietary J9[125] but has since relicensed the project and donated it to the Eclipse Foundation. JRockit is a proprietary implementation that was acquired by Oracle and incorporated into subsequent OpenJDK versions.

• Official Java SE Downloads
• Sun Java Supported versions and EOL
• Downloads archive for older version of Java
• JDK Releases
• The Java Version Almanac