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Frames collector and heap decisions around service goals, workload evidence, pause distributions, live set, and deployment limits.
Constructs a service directly with explicit collaborators and verifies behavior without Spring startup or framework-owned concerns.
Uses multiple thread dumps, CPU correlation, lock ownership, executor context, and request evidence to distinguish deadlock, contention, blocking, and hot loops.
Contrasts abstraction's caller-facing contract with encapsulation's control of internal state and shows how one object can use both.
Makes duplicate-key behavior explicit through validation, merge policies, grouping, and deterministic map selection.
Treats interruption as a cooperative request, preserves interrupt status, defines cleanup, and separates cancellation signals from guaranteed task termination.
Uses Optional to model absence at return boundaries and avoids eager defaults, null Optionals, unsafe get calls, and awkward field or parameter usage.
Explains decimal construction, scale, equality, rounding, and why BigDecimal needs a money contract around it.
Builds an immutable Java type through valid construction, final state, defensive copying, controlled exposure, and safe sharing.
Triages heap, Metaspace, native, direct-buffer, thread, and container exhaustion using preserved evidence before changing limits.
Diagnoses queued work, blocked workers, nested submissions, common-pool contention, downstream waits, and misleading CPU symptoms.
Describes lazy iterator execution, state-machine behavior, early termination, resource disposal, and repeat-enumeration consequences.
Compare synchronous enumeration with async streaming and explain when IAsyncEnumerable helps with large or delayed data.
Chooses immutable values and controlled mutable entities based on identity, concurrency, invariants, allocation cost, and update semantics.
Builds a small immutable money type with explicit scale, rounding, arithmetic, ordering, and value equality.
Builds a frozen dataclass around Decimal with explicit scale, validation, arithmetic, ordering, and value equality.
Implements a small in-memory fixed-window rate limiter with per-key counters.
Implements a small LRU cache using a dictionary plus linked list for O(1) get and put.
Uses inheritance only for stable behavioral subtyping and tests whether derived objects preserve the promises callers rely on.
Resolves Java's pass-by-value confusion by separating mutation through a copied reference from reassignment of the caller's variable.
Balances declarative transformations with explicit control flow when allocation, early exit, mutation, diagnostics, or complex state matters.
Predicts when an in-memory LINQ pipeline runs and prevents repeated work, changed results, and hidden side effects.
Chooses when to keep a sequence lazy and when to create a stable collection with ToList, ToArray, or another deliberate materialization.
Implements interval merging for scheduling-style time ranges with sorted output.