Java 8 - Features / Enhancements

---

Java 8 - Language & Core Library Enhancements

Lambda Expressions

• Syntax → (x, y) -> x + y
• Enables functional programming style.
• Replaces anonymous classes.
• Target typing support.
• Captures only effectively final variables.
• Compiled using invokedynamic (not inner classes).

Functional Interfaces

• @FunctionalInterface
• Exactly one abstract method (SAM).
• Built-in interfaces:
  • Predicate
  • Function
  • Consumer
  • Supplier
  • UnaryOperator
  • BinaryOperator
• Supports default and static methods.

Default & Static Methods in Interfaces

• Backward compatibility for interface evolution.
• Diamond problem resolution using explicit override.
• Static methods belong to interface (not inherited).

Method References

• Class::staticMethod
• object::instanceMethod
• Class::instanceMethod
• Class::new (constructor reference)

Repeating Annotations

• Same annotation can be applied multiple times.
• Uses container annotation internally.

Type Annotations

• Can annotate any use of a type.
• Useful for static analysis tools (e.g., null safety).

Optional

• Avoids NullPointerException.
• Methods:
  • map
  • flatMap
  • filter
  • orElse
  • orElseGet
  • orElseThrow
• Not recommended for fields or serialization.

---

Java 8 - Collections & Concurrency

Streams API

• Functional-style collection processing.
• Pipeline model (Source → Intermediate → Terminal).
• Lazy evaluation.
• Stateless vs Stateful operations.
• Uses Spliterator internally.
• Common operations:
  • filter
  • map
  • flatMap
  • reduce
  • collect

Parallel Streams

• Uses ForkJoinPool.commonPool().
• Automatic workload splitting.
• Good for CPU-bound tasks.
• Avoid for:
  • I/O-heavy tasks
  • Small datasets
  • Shared mutable state

Collectors API

• Collectors.toList()
• toSet()
• toMap()
• groupingBy()
• partitioningBy()
• Downstream collectors.
• Custom collector support.

New Map Methods

• forEach
• computeIfAbsent
• computeIfPresent
• compute
• merge
• replaceAll

ConcurrentHashMap Enhancements

• forEach
• reduce
• search
• Better parallelism and scalability.

HashMap Improvement

• Bucket converts from LinkedList → Red-Black Tree.
• Treeification threshold = 8 entries.
• Improves worst-case:
  • O(n) → O(log n)

---

Java 8 - Date & Time API (java.time)

Core Classes

• LocalDate
• LocalTime
• LocalDateTime
• ZonedDateTime
• Instant

Additional Classes

• Duration (time-based)
• Period (date-based)
• DateTimeFormatter

Key Improvements

• Immutable
• Thread-safe
• Clear timezone handling
• Replaces java.util.Date and Calendar

---

Java 8 - JVM & Language Runtime

Metaspace

• Replaces PermGen.
• Uses native memory.
• Eliminates OutOfMemoryError: PermGen space.

Nashorn JavaScript Engine

• Run JavaScript inside JVM.
• Removed in Java 15.

Compact Profiles

• Subset JREs for embedded systems.

---

Java 8 - Concurrency Enhancements

CompletableFuture

• Asynchronous programming.
• Non-blocking pipelines.
• thenApply
• thenCompose
• thenCombine
• Exception handling support.
• Supports async and sync execution.

StampedLock

• Supports:
  • Optimistic read
  • Read lock
  • Write lock
• Better performance than traditional read-write locks in some cases.

---

Java 8 - New Utilities & APIs

Base64 API

• java.util.Base64
• Basic, URL, and MIME encoders.

Unsigned Arithmetic

• Integer.divideUnsigned()
• compareUnsigned()
• toUnsignedLong()

StringJoiner

• Custom delimiter.
• Optional prefix and suffix.

Files & IO Enhancements

• Files.lines(Path) → Stream of lines.
• Files.walk() → Recursive traversal.
• Files.find() → Search with predicate.
• Stream-based file processing.

Arrays Enhancements

• Arrays.parallelSort()

String Enhancements

• String.join()
• String.chars() → IntStream
• String.codePoints()

Comparator Enhancements

• thenComparing()
• naturalOrder()
• reverseOrder()
• Comparator chaining.

---

---

Table of contents

• Optional
• Stream API