- Stacks
Last in, first out — everything happens at one end, so everything is O(1). Building one on an array, the balanced-brackets problem that is the reason interviewers ask about stacks, why the call stack is one, and why you should never use java.util.Stack.
- Spring Boot – Mapping DTOs with MapStruct
Generated mapping code instead of hand-written getters and setters, checked at compile time. Writing a mapper, handling nested objects and custom expressions — and the annotation-processor ordering that makes MapStruct and Lombok work together, because getting it wrong produces mappers that compile and map nothing.
- iOS – Getting Started
What you actually need to build an iOS app, what each piece of Xcode is for, and the anatomy of a project — targets, schemes, build configurations and the .xcodeproj nobody can read. Ending with a project generated from a manifest instead, so a build setting change is a line in a diff rather than an opaque edit.
- Python – Tuples
Tuples and why an immutable sequence earns its place next to the list. Unpacking, returning more than one value, the starred target, named tuples, and the one-element tuple that catches everybody.
- CompletableFuture
CompletableFuture runs work on another thread and lets you describe what should happen when it finishes — without blocking to wait for it. It is how you stop making a caller wait for three slow things in sequence when they could happen at once. Starting work supplyAsync when you want a value back,…