Java 8 features

1. Lambda Expressions
   Lambda expressions introduce a concise way to represent anonymous functions. They enable functional programming and simplify the syntax for implementing interfaces with a single abstract method.
   Example: (parameters) -> expression
2. Functional Interfaces
   An interface with a single abstract method (SAM) is called a functional interface. Common examples include Runnable, Callable, and custom functional interfaces annotated with @FunctionalInterface.
3. Stream API
   The Stream API facilitates functional-style operations on collections and other data sources. It supports operations like map, filter, and reduce for data processing. Streams can be either sequential or parallel.
4. Default Methods
   Interfaces can now have methods with a default implementation using the default keyword. This allows developers to add new methods to interfaces without breaking existing implementations.
5. Optional Class
   The Optional class is a container object that represents the presence or absence of a value. It helps avoid NullPointerException by providing methods like isPresent, ifPresent, and orElse.
6. New Date and Time API
   Java 8 introduced a new, thread-safe date and time API under the java.time package. It includes classes like LocalDate, LocalTime, LocalDateTime, and ZonedDateTime.
7. Nashorn JavaScript Engine
   Java 8 includes a new JavaScript engine called Nashorn, which provides better performance and allows embedding JavaScript code in Java applications.
8. Stream Enhancements in Collections
   Collections received methods like stream() and parallelStream() to enable easier integration with the Stream API.
9. Method References
   Method references provide a shorthand syntax for calling methods. They use the :: operator and can reference static methods, instance methods, or constructors.
10. Collectors
    The Collectors utility class provides methods for transforming streams into different forms, such as lists, sets, or maps, and for performing reduction operations like summing and averaging.
11. Base64 Encoding and Decoding
    The java.util.Base64 class provides methods to encode and decode data in Base64 format.
12. Parallel Array Sorting
    Java 8 added methods to sort arrays in parallel, improving performance for large datasets.
13. Concurrent Accumulators
    The java.util.concurrent package introduced classes like LongAdder and DoubleAdder for high-performance thread-safe operations.
14. CompletableFuture
    The CompletableFuture API in java.util.concurrent simplifies asynchronous programming by providing a rich set of methods for combining and chaining tasks.
15. Annotations on Types
    Java 8 allows annotations to be applied to types, enhancing the ability to define validation and processing rules.
16. PermGen Space Removal
    The Permanent Generation (PermGen) space was removed in favor of the Metaspace, which automatically adjusts to accommodate class metadata and reduces out-of-memory errors.
17. Repeating Annotations
    Developers can now use the same annotation multiple times on the same declaration. This feature is enabled by the @Repeatable annotation.
18. Static Methods in Interfaces
    Interfaces can now include static methods, allowing utility methods to be encapsulated within the interface.
19. Improved Type Inference
    Java 8 improved type inference, making it easier to work with generics, especially in lambda expressions.
20. Fork/Join Pool Enhancements
    Enhancements were made to the fork/join framework to better support parallelism in modern hardware architectures.

Each feature introduced in Java 8 significantly improved productivity, performance, and ease of programming, making it a revolutionary release in the Java ecosystem.