7.JVM

A concise roadmap for studying JVM memory, class loading, JIT compilation, garbage collection, and production diagnostics.

A production Java incident workflow covering CPU, latency, threads, heap, GC, native memory, I/O, and evidence preservation.

Reachability-based reclamation, GC roots, object liveness, and why garbage collection manages memory rather than arbitrary external resources.

Loading, linking, initialization, use, unloading, and class-loader identity in the JVM.

Heap, stacks, method-area metadata, program counters, native stacks, and the difference between JVM specification concepts and HotSpot implementation details.

A hypothesis-driven performance tuning workflow from SLO and bottleneck identification through measurement, change, and regression validation.

Mark-sweep, copying, compaction, generational collection, and the throughput/latency/space trade-offs behind modern JVM collectors.

Static initialization, superclass initialization, instance field initializers, initializer blocks, and constructors in Java.

How HotSpot commonly allocates objects, including TLABs, young-generation allocation, large objects, promotion, and why exact rules depend on the collector.

A durable overview of Serial, Parallel, G1, ZGC, Shenandoah-style collector goals without treating historical defaults as permanent facts.

How custom class loaders define classes, delegation, namespace isolation, and the operational risks of loader leaks.

JIT escape analysis, scalar replacement, lock elimination, and why stack allocation should not be treated as a guaranteed Java object-allocation rule.

Collector-selection principles and JVM flags, with emphasis on verifying support against the deployed JDK instead of copying obsolete flag recipes.

From bytecode allocation through class readiness, heap allocation, zero initialization, object headers, and Java constructor execution.

An overview of JVM garbage collection: reachability, generations, collection cycles, pauses, concurrent work, and the metrics that matter operationally.

Conceptual object layout in HotSpot: headers, instance fields, alignment, compressed references, and why byte offsets are implementation-specific.

Strong, soft, weak, phantom, and reachability-related references, with practical cautions about caches and cleanup.

Direct-pointer and handle-based object-reference models, and why Java code should not depend on a particular physical object-address representation.

How to distinguish heap retention, allocation pressure, Metaspace, direct/native memory, and thread-related out-of-memory failures.

A practical guide to JFR, jcmd, thread dumps, heap dumps, profilers, GC logs, and OS/container metrics.

A measurement-first approach to JVM memory and GC parameters, avoiding obsolete one-size-fits-all tuning recipes.

What to extract from GC logs: pause distribution, allocation pressure, live-set behavior, promotion, full collections, and concurrent-cycle health.