Java Architect Essentials

Nov 16, 2023 · Backend Development

Why Does HashMap.keySet() Iterate Twice? Uncovering Java’s Internal Iterator Mechanics

This article explains why iterating a Java HashMap with keySet() results in two traversals, detailing the internal iterator creation, the role of KeyIterator and HashIterator classes, and how the do‑while loop in HashIterator’s constructor locates the first entry, with code examples and bytecode analysis.