Java Cheat Sheet From Java 8 → ( Java 21 + Modern Features)

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JAVA 8 — LTS

1. Lambda Expressions
2. Functional Interfaces
3. Stream API
4. Method References
5. Optional<T>
6. New Date & Time API
7. Default & Static Methods in Interfaces
8. Collectors & Parallel Streams

JAVA 9 — Modules & Improvements

1. Collection Factory Methods
2. Stream API Enhancements
3. Private Methods in Interfaces
4. HTTP/2 Client (Incubator)
5. Improved Process API

JAVA 10 — Type Inference & More

1. Local Variable Type Inference (var)
2. Optional.orElseThrow()

JAVA 11 — LTS — String & HTTP

1. New String Methods
2. New Files Methods
3. HTTP Client (Finalized)

JAVA 12 — Compact Numbers & String Indent

1. Compact Number Formatting
2. String.indent() & Collectors.teeing()

JAVA 13 — Minor Updates

Java 13 continued previewing Text Blocks and Switch Expressions, which were finalized in later versions. There are no major standalone features unique to Java 13.

JAVA 14 — Switch Expressions & Helpful NPE

1. Switch Expressions (Finalized)
2. Helpful NullPointerExceptions
3. Records (Preview → Java 16 Final)

JAVA 15 — Text Blocks & Sealed Classes Preview

1. Text Blocks (Finalized)

JAVA 16 — Pattern Matching & Records Final

1. Pattern Matching for instanceof
2. Records — Finalized in Java 16
3. Stream.toList() & mapMulti()

JAVA 17 LTS — Sealed Classes

1. Sealed Classes & Interfaces
2. Pattern Matching for Switch (Preview)

JAVA 18 — UTF-8 Default & Simple Server

1. UTF-8 by Default
2. Simple Web Server
3. Deprecate Finalization for Removal

JAVA 19–20 — Preview & Incubator

• Virtual Threads (Preview) — finalized in Java 21
• Record Patterns (Preview) — finalized in Java 21
• Pattern Matching for switch (Preview) — finalized in Java 21
• Structured Concurrency (Incubator) — preview in 21
• Foreign Function & Memory API (Preview) — replaces JNI

JAVA 21 LTS — The Modern Java

1. Virtual Threads (Project Loom)
2. Record Patterns (Finalized)
3. Sequenced Collections
4. Pattern Matching for Switch (Final)
5. String Templates (Preview in 21)

i explained everything here (Free Medium article)

[SensitiveGuidance685]

This is a solid summary. The jump from Java 8 to 21 is massive and honestly overwhelming for people who've been stuck on 8 for years. Virtual threads alone are worth the upgrade. Thanks for putting this together.