NOTE
Java 8 Language and Library Features
Lambdas, functional interfaces, streams, Optional, default methods, java.time, and CompletableFuture introduced around Java 8.
This is a historical learning note and may contain outdated or incomplete understanding.
Java 8 was a major shift toward functional-style APIs. Key additions include lambdas/method references, functional interfaces, streams, interface default/static methods, Optional, the java.time date/time API, and CompletableFuture.
Streams describe transformations over data; they are not automatically faster than loops, and parallel streams share execution resources that may be unsuitable for blocking/latency-sensitive work.
Optional is useful as an explicit “maybe value” return type, not as a universal replacement for every nullable field/parameter.
java.time should be preferred over legacy mutable date/calendar APIs for most new code.