Java 8, 17, 21 features

 

✅ Java 8 – Key Features & Descriptions

Feature	Description
Lambdas	Enables writing anonymous functions (e.g., (x) -> x * 2) for cleaner, functional-style code.
Streams API	Provides a declarative way to process collections using operations like filter, map, and reduce.
Functional Interfaces	Interfaces with a single abstract method, used with lambdas (e.g., Runnable, Predicate).
Default/Static Methods in Interfaces	Allows methods in interfaces to have default implementations.
Optional	A container that may or may not hold a value, reducing null checks.
java.time API	A modern, immutable, and thread-safe API for handling dates and times (LocalDate, Instant, etc.).
Nashorn Engine	Embedded JavaScript engine (now deprecated in later versions).

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✅ Java 17 – Key Features & Descriptions

Feature	Description
Records	Concise syntax to declare immutable data classes without boilerplate (record User(String name, int age) {}).
Pattern Matching for instanceof	Simplifies type checks and casting (if (obj instanceof String s) { ... }).
Sealed Classes	Restricts which classes can extend or implement a class/interface. Improves control over inheritance.
Switch Expressions	Enhances switch with expression syntax and yield, making it more powerful and type-safe.
Text Blocks	Multi-line string literals using """, useful for SQL, JSON, or HTML in code.
Strong Encapsulation	Internal JDK APIs are hidden unless explicitly opened, improving security and modularity.
G1/ZGC Enhancements	Improved low-pause-time garbage collectors for better performance.

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✅ Java 21 – Key Features & Descriptions

Feature	Description
Virtual Threads (Project Loom)	Lightweight threads managed by the JVM that dramatically improve scalability and simplify concurrency.
Record Patterns	Enables decomposition of records in pattern matching for cleaner, readable conditional logic.
Pattern Matching for switch	Allows rich, type-safe, and expressive switch statements with pattern checks.
String Templates (Preview)	Simplifies and secures string interpolation using STR."Hello, \{name}".
Scoped Values	A lightweight alternative to ThreadLocal for managing context across threads (especially virtual threads).
Foreign Function & Memory API (FFM)	Modern, safe alternative to JNI for calling native code and managing off-heap memory directly.

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🔄 Migration Summary

Java 8 → Java 17

• Refactor code to use lambdas and streams.

• Replace POJOs with records where applicable.

• Replace Date/Calendar with java.time.

• Upgrade third-party libraries for Java 17 support.

• Use new switch, var, and text blocks for better readability.

Java 17 → Java 21

• Replace thread pools with virtual threads for I/O-heavy tasks.

• Simplify instanceof and switch statements with pattern matching.

• Adopt record patterns for better DTO handling.

• Use ScopedValues instead of ThreadLocal.

• Integrate with native libraries using FFM if needed.

✅ Java 8 – Key Features (Released 2014)

The foundation of modern Java programming.

🌟 Core Features:

• Lambdas
  list.forEach(item -> System.out.println(item));

• Streams API
  Declarative data processing: stream().filter().map().collect()

• Functional Interfaces
  @FunctionalInterface, Function, Predicate, Consumer

• Default & Static methods in interfaces

• java.time API
  Modern date/time handling (LocalDate, ZonedDateTime)

• Optional
  Safe null handling: Optional.ofNullable(...)

• Nashorn JavaScript Engine

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✅ Java 17 – Key Features (Released 2021, LTS)

A stable, modernized Java platform with significant enhancements.

🧱 Language Features:

• Records
  Concise immutable data classes

  record User(String name, int age) {}
  

• Pattern Matching for instanceof

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

• Sealed Classes
  Control inheritance

  public sealed class Shape permits Circle, Square {}
  
  final class Circle extends Shape {}
  final class Square extends Shape {}

• Switch Expressions
  Safer, expression-style switch with yield

String result = switch (day) {

    case MONDAY -> "Start";

    case FRIDAY -> "End";

    default -> "Mid";

};

• Text Blocks
  Multiline strings with """

⚙️ JVM/Runtime:

• New Garbage Collectors: ZGC, G1 improvements

• Strong encapsulation of JDK internals (no illegal reflective access)

• Removed: Applet API, Nashorn, RMI Activation

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✅ Java 21 – Key Features (Released 2023, LTS)

Java 21 is concurrency-optimized, future-forward, and productivity-focused.

🚀 Language & Platform:

• Virtual Threads (Project Loom – Finalized)

  try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
      executor.submit(() -> System.out.println("Hello from virtual thread"));
  }
  

  • Lightweight threads for scalability

  • Reduce need for reactive/async frameworks

• Record Patterns
  Powerful deconstruction in pattern matching

  record Point(int x, int y) {}
  void print(Object obj) {
      if (obj instanceof Point(int x, int y)) {
          System.out.println(x + "," + y);
      }
  }

• Pattern Matching for switch
  Type-safe, expressive branchingstatic String handle(Object o) {

      return switch (o) {

          case String s -> "A string: " + s;

          case Integer i -> "An integer: " + i;

          default -> "Something else";

      };

  }

• String Templates (Preview)
  Safer string interpolation: STR."Hello, \{name}!"

• Scoped Values (vs ThreadLocal)
  Replaces thread-local variables for immutable data sharing between threads.

• Foreign Function & Memory API (FFM)
  Interact with native code safely, no JNI needed.

• Sequenced Collections (JEP 431)

  New interfaces with stable iteration order:

  • SequencedCollection

  • SequencedSet

  • SequencedMap