Table of contents Why does Map exist? What would life be without it? HashMap: the street analogy hashCode() and equals() explained Collisions: when two people share a house Load factor and resizing The other Map types The one rule you must never break Interview problems where Map is the answer SECTION 1. Why does Map even exist? Before touching any internals, let's nail the real problem Map was built to solve because if you understand the problem, everything else makes sense automatically. Imagine you work at a hotel front desk. 1,000 guests are checked in. Your boss walks over and asks: The scenario "Is John Smith in room 847?" Enter fullscreen mode Exit fullscreen mode You have two choices for how to answer that. The hook label is the key. The room key hanging on it is the value. You provide a key, you get the value back instantly. One sentence summary: A Map lets you associate any key with any value and look that value up in O(1) time without scanning through everything.…