Modern Java Notes

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Since Java 11 the platform includes a modern HTTP client with synchronous and asynchronous requests and HTTP/2 support.

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What changed in each release since Java 8, which old habits it replaces, and what to reach for in new code today.

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A sealed type names exactly which types may extend it, which lets the compiler check that a pattern switch covers every case.

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Modules add a boundary above packages: a module declares what it needs and what it exposes, and everything else stays private.

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A Future is a placeholder for a result that is not ready yet. CompletableFuture adds composition, so results can be chained without blocking.

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An executor separates submitting work from running it, so threads are reused instead of created per task.

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Path names a location and Files performs the operations. Together they replaced the older File class for almost every purpose.

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DateTimeFormatter converts between text and date time values, and ZoneId handles the region rules that make time zones difficult.

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Instant marks a point on the timeline; Duration measures time based amounts and Period measures date based ones.

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The modern date and time API is immutable, thread safe and clearly named, and it replaced the older Date and Calendar classes entirely.

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A parallel stream splits the work across threads. It helps less often than people expect, and it breaks silently when the rules are ignored.

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Collectors turn a stream into a collection, a map or a summary, and grouping is where they become genuinely powerful.