Java 8 (March 2014)

• Lambda Expressions: Introduced to support functional programming, allowing for concise and readable anonymous function expressions. Example: (a, b) -> a + b.
• Streams API: Provides a powerful way to process collections of objects using a functional approach. It supports operations like map(), filter(), reduce(), and parallel processing.
• Optional Enhancements: The Optional class is introduced to avoid NullPointerException. It helps represent the absence of a value more explicitly.
• Default and Static Methods in Interfaces: Interfaces can now have methods with default implementations, reducing the need for implementing boilerplate code.
• New Date and Time API (java.time): A modern and comprehensive API for date and time management, replacing the outdated java.util.Date. Classes like LocalDate, LocalTime, LocalDateTime provide a more intuitive way to work with dates.
• Nashorn JavaScript Engine: A new JavaScript engine that allows embedding and running JavaScript code in Java applications.
• Method References: Provides a shorthand syntax for lambdas when referring to a method, using Class::method notation.
• Collectors: A utility to accumulate elements processed in a stream into various collections (e.g., List, Set, etc.).
• ParallelSort: Optimized parallel sorting for large arrays, improving performance when sorting with multiple threads.
• Type Annotations: Allows annotations to be used in more places, such as on generic types.
• CompletableFuture: A more powerful alternative to Future, allowing asynchronous programming with better error handling and chaining operations.

Java 9 (September 2017)

• Modules (Project Jigsaw): Introduces a module system to better structure large applications, allowing for strong encapsulation and better modularity of code.
• JShell (Java REPL): An interactive tool for evaluating snippets of code, providing immediate feedback, which is useful for experimentation and learning.
• Private Interface Methods: Interfaces can now include private methods to share code between default methods, improving code reuse.
• Collection Factory Methods: Convenient ways to create immutable collections using List.of(), Set.of(), Map.of().
• Stream API Enhancements: Adds methods like takeWhile(), dropWhile(), and ofNullable() to the Stream API, making it easier to process sequences of data.
• Optional Enhancements: Adds methods like ifPresentOrElse() and or() to handle absent values more effectively.
• Try-With-Resources Enhancements: Simplifies the syntax for try-with-resources by allowing resources declared outside the try block.
• Multi-Release JAR Files: A feature that allows JAR files to contain different class versions for different Java runtime versions, making it easier to maintain backward compatibility.

Java 10 (March 2018)

• Local-Variable Type Inference (var): Introduces the var keyword, allowing the compiler to infer the type of local variables, reducing boilerplate code.
• Unmodifiable Collectors: Adds methods like Collectors.toUnmodifiableList(), Collectors.toUnmodifiableSet() to easily create unmodifiable collections from streams.
• Optional.orElseThrow(): A no-argument version of orElseThrow() that throws NoSuchElementException by default.
• Application Class-Data Sharing (AppCDS): Improves startup time by sharing common class metadata across multiple JVMs.
• Garbage Collector Interface: Introduces a cleaner and more flexible garbage collector interface, allowing easier garbage collector selection and configuration.

Java 11 (September 2018)

• New String Methods: Adds several utility methods to String such as lines(), strip(), repeat(), and isBlank(), simplifying common string operations.
• Local-Variable Syntax for Lambda Parameters: Allows the use of var in lambda expressions, improving consistency with other parts of the language.
• HTTP Client API: Introduces a new, modern HTTP client (java.net.http.HttpClient) that supports HTTP/2, WebSockets, and more, making network communication simpler and more efficient.
• File Methods (Files.writeString(), Files.readString()): Simplifies file I/O by adding methods for directly reading and writing strings to files.
• Running Java Files without Compilation: Allows Java source files to be run directly without prior compilation, simplifying quick testing and development.
• Deprecation of Nashorn: Deprecates the Nashorn JavaScript engine, signaling its eventual removal.

Java 12 (March 2019)

• Switch Expressions (Preview): Introduces switch expressions, allowing switch to be used as both a statement and an expression, enabling more concise and functional-style code.
• Pattern Matching for instanceof (Preview): Simplifies the pattern for type checks and casting, reducing boilerplate when using instanceof.
• JVM Constants API: Introduces a new API to represent and work with constants in the JVM.
• New Collectors (Collectors.teeing()): Introduces Collectors.teeing(), allowing the combination of two collectors into one, producing a combined result.
• G1 Garbage Collector Enhancements: Improves performance of the G1 garbage collector, reducing its pause times.

Java 13 (September 2019)

• Text Blocks (Preview): Introduces text blocks, a new syntax for multi-line string literals, making it easier to write long strings or code snippets.
• Switch Expressions (Second Preview): Further refinements to switch expressions, making them more robust.
• Dynamic CDS Archives: Reduces the footprint by allowing the JVM to archive classes dynamically at runtime, optimizing memory use.

Java 14 (March 2020)

• Pattern Matching for instanceof: Finalizes pattern matching for instanceof, allowing for more concise and readable code.
• Records (Preview): Introduces records, a new kind of class that is meant to hold immutable data, with minimal boilerplate code (i.e., auto-generated getters, equals(), hashCode(), and toString() methods).
• Text Blocks (Second Preview): Continued improvements to text blocks, incorporating feedback from the first preview.
• Helpful NullPointerExceptions: Adds more informative null pointer exception messages, showing which variable was null.
• Switch Expressions (Standard): Switch expressions are now a standard feature in the language, allowing concise, functional-style code with switch statements.

Java 15 (September 2020)

• Text Blocks (Standard): Finalizes text blocks, allowing them to be used in production code for multi-line strings.
• Pattern Matching for instanceof (Second Preview): Further improvements to pattern matching for instanceof, making it more versatile.
• Records (Second Preview): Continued development of records, incorporating feedback and refinements.
• Sealed Classes (Preview): Introduces sealed classes, allowing developers to restrict which classes can inherit from a particular class, improving encapsulation and security.
• Hidden Classes: Introduces hidden classes, which are not discoverable by reflection and can be used by frameworks that dynamically create classes.

Java 16 (March 2021)

• Pattern Matching for instanceof (Standard): Finalizes pattern matching, making it a permanent part of the language.
• Records (Standard): Records become a standard feature, providing a concise way to declare immutable data classes.
• Sealed Classes (Second Preview): Continued preview of sealed classes with more refinements.
• Vector API (Incubator): Introduces the Vector API for working with vectorized computations, aimed at improving performance for certain workloads.
• Foreign Linker API (Incubator): Provides a new API for interfacing with native code, making it easier and safer to call C libraries from Java.

Java 17 (September 2021) – LTS

• Sealed Classes (Standard): Sealed classes are finalized, allowing developers to limit which classes can extend or implement a given class or interface.
• Pattern Matching for switch (Preview): Extends pattern matching to switch expressions and statements, making them more powerful and versatile.
• Records Enhancements: Local and anonymous classes can now be records, providing even more flexibility in defining concise data classes.
• Foreign Function & Memory API (Incubator): A preview of the new API that makes it easier to interact with native memory and functions, enhancing native interoperation.
• Context-Specific Deserialization Filters: Improves security by allowing developers to define more fine-grained filters for deserialization.
• Vector API (Second Incubator): Continued development of the Vector API, with improvements for vectorized computations.
• Strong Encapsulation by Default: The JDK’s internal elements are now strongly encapsulated by default, improving security and reliability.

Java 18 (March 2022)

• Simple Web Server: Introduces a minimal web server that can be used for testing or prototyping purposes.
• UTF-8 by Default: UTF-8 becomes the default character encoding for the JVM, ensuring consistency across platforms.
• Vector API (Third Incubator): Further improvements to the Vector API, with enhanced performance for vectorized workloads.
• Pattern Matching for switch (Second Preview): Continued preview of pattern matching for switch expressions, adding more features and refinements.
• Foreign Function & Memory API (Second Incubator): Further development of the Foreign Function & Memory API, enhancing interoperability with native code.

Java 19 (September 2022)

• Virtual Threads (Preview): Introduces virtual threads, which are lightweight threads designed to simplify concurrency and scale better than traditional threads.
• Structured Concurrency (Incubator): Introduces structured concurrency to make concurrent code easier to write and reason about by grouping multiple tasks and handling them as a unit.
• Pattern Matching for switch (Third Preview): Further improvements to switch pattern matching.
• Record Patterns (Preview): Allows deconstructing records directly in instanceof patterns, making it easier to extract fields.
• Foreign Function & Memory API (Third Incubator): Further progress on native interoperation with this API.

Java 20 (March 2023)

• Virtual Threads (Second Preview): Improvements to virtual threads, continuing development to make them more stable and performant.
• Structured Concurrency (Second Incubator): Further enhancements to structured concurrency, simplifying concurrent programming.
• Pattern Matching for switch (Fourth Preview): Continued refinement of pattern matching in switch statements.
• Record Patterns (Second Preview): Further development of record patterns, making it easier to work with records in pattern matching.
• Scoped Values (Incubator): Introduces scoped values, which provide a way to share immutable data across multiple threads.

Java 21 (September 2023) – LTS

• Virtual Threads (Standard): Virtual threads are finalized, making them a standard feature in the JVM, offering a scalable solution for concurrency.
• Pattern Matching for switch (Standard): Pattern matching for switch statements becomes a standard feature, enabling concise and expressive code.
• Record Patterns (Standard): Record patterns become a standard feature, simplifying the deconstruction of records in pattern matching.
• Unnamed Classes and Instance Main Methods: Simplifies development by allowing unnamed classes and instance main methods, reducing boilerplate in simple programs.
• Sequenced Collections: Introduces sequenced collections, a new collection type that maintains insertion order, filling a gap in the collection framework.
• Foreign Function & Memory API (Standard): The Foreign Function & Memory API becomes a standard feature, improving the JVM’s ability to interact with native code and memory.
• String Templates (Preview): Introduces string templates, simplifying the construction of strings by allowing embedded expressions directly in string literals.
• Scoped Values (Second Incubator): Continued development of scoped values, providing a way to share immutable data across threads.

Each feature is explained in greater detail to highlight its importance and use cases from Java 8 to Java 21. Let me know if you need more clarification or specific examples!