Java Comparators and Ordered Collections
Why TreeSet and TreeMap drop elements when a Comparator disagrees with equals, and how to write comparators that obey the full contract.
~6 min readread →
Developer interview notes & guides — Page 6
Focused explanations and longer guides, with worked scenarios, common mistakes and interview exercises across every chapter.
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Showing 121–144 of 200 articles
Java CompletableFuture Error Composition
How exceptions travel through CompletableFuture chains, when to use exceptionally, handle or whenComplete, and why causes arrive wrapped.
~7 min readread →
Java Concurrent Collections and Compound Operations
Why check-then-act on ConcurrentHashMap still races, and how merge, compute and putIfAbsent make compound updates atomic per key.
~7 min readread →
Java equals() and hashCode(): The Rules and HashMap Bugs
The equals and hashCode contract explained: why equal objects need equal hash codes, how HashMap uses both, and how to write a correct pair.
~6 min readread →
Java Exception Handling: Where to Catch, Wrap and Rethrow
Checked vs unchecked exceptions in Java, where to catch, when to wrap with a cause, and how to avoid swallowing failures at the wrong layer.
~7 min readread →
Java Garbage Collection and Retained Objects
How Java memory leaks happen despite garbage collection: GC roots, reachability, retained size, and finding the reference chain in a heap dump.
~8 min readread →
Java Immutable Objects and Defensive Copies
How to make a class immutable in Java: final fields, no setters, defensive copies of mutable inputs and outputs, and safe publication.
~6 min readread →
Java Time Types and Zone-Aware Decisions
When to use Instant, LocalDateTime, ZonedDateTime and OffsetDateTime, and how daylight saving gaps and overlaps break naive date code.
~7 min readread →
Java synchronized Explained: Locks, Visibility and Reentrancy
What synchronized guarantees in Java: mutual exclusion, visibility and reentrancy, plus how to guard multi-field invariants with one lock.
~7 min readread →
Java Thread Visibility and Happens-Before
Why one Java thread may never see another's write, what volatile guarantees, and how happens-before rules make publication safe.
~7 min readread →
Java Virtual Threads and Blocking Workloads
When Java 21 virtual threads help, why they do not speed up CPU-bound work, and how pinning, pooling and resource limits trip teams up.
~8 min readread →
JavaScript Array Copies and Shared Objects
Why [...arr] and slice() copy the array but not the objects inside it, and how to choose a targeted update, structuredClone or JSON safely.
~7 min readread →
JavaScript reduce(): Initial Value, Accumulator and Mutation
How Array.prototype.reduce works, why the initial value matters for empty arrays, and when mutating the accumulator is safe or quadratic.
~8 min readread →
Async/Await in Loops: forEach vs for...of vs Promise.all
Why await inside forEach does not wait, how for...of runs tasks in sequence, and how to run async work in parallel with a concurrency limit.
~7 min readread →
JavaScript Event Delegation and Dynamic Elements
One click listener on a parent can serve rows added later. How closest(), contains() and composedPath() keep delegation from misfiring.
~8 min readread →
JavaScript Memory Leaks and Retained References
A forgotten listener kept 200 models and 76 MB alive in Node. How to prove a leak with GC and heap snapshots, then break the retaining path.
~7 min readread →
ES Module Live Bindings vs CommonJS: Interview Guide
Why ES module imports see later changes to exported variables, why CommonJS copies values, and how live bindings affect circular imports.
~7 min readread →
Promise finally() in JavaScript: Cleanup Without Losing Errors
How promise finally() passes results and errors through, when a finally callback overrides the outcome, and how try/finally compares.
~7 min readread →
WeakMap vs Map in JavaScript: Garbage Collection and Leaks
Why WeakMap keys do not keep objects alive, why WeakMaps cannot be iterated, and how to attach caches and private data without leaking memory.
~8 min readread →
Node.js Blocking Work and Request Latency
Why a 170 ms synchronous loop in one Node.js request delays every other request, how to measure loop delay, and when to chunk or use workers.
~6 min readread →
Node.js Buffers and UTF-8: Fixing Corrupted Text Across Chunks
Why decoding each chunk with toString() corrupts non-ASCII text, how StringDecoder fixes it, and when Node.js bytes must never become strings.
~6 min readread →
Node.js Child Processes and Argument Safety
How a filename becomes shell injection with exec, why execFile and spawn with argument arrays avoid it, and the -- trick for argument injection.
~6 min readread →
Node.js Async Error Handling: Floating Promises and try/catch Gaps
Where async errors escape try/catch in Node.js, why a floating promise kills the process, and how to wrap causes and catch at one boundary.
~6 min readread →
Node.js File Paths and Traversal Prevention
Why path.join doesn't stop ../ traversal, how a startsWith check and a symlink both leak files, and a Node.js containment check that holds up.
~6 min readread →
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