Map & Set in Java
From the Java cheat sheet · Arrays & Collections · verified Jul 2026
Map & Set
Key-value pairs and unique collections.
java
// Quick Reference
Map<String, Integer> m = new HashMap<>();
m.put("a", 1); m.get("a");
Set<String> set = new HashSet<>();
set.add("x"); set.contains("x");💡 HashMap keys are unique - putting an existing key overwrites its value.
⚡ getOrDefault and merge make counting and accumulation one-liners.
📌 HashMap/HashSet are unordered; use LinkedHashMap or TreeMap for ordering.
🟢 Iterate a Map via entrySet() to access keys and values together.
mapset
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