Maps: iterate entrySet, not keySet plus get

Iterating keys and calling get for each one hashes every key twice. entrySet gives the key and value together in a single pass.

Code

Map<String, Integer> tokens = new TreeMap<>();
tokens.put("ava", 60);
tokens.put("ben", 150);

for (Map.Entry<String, Integer> e : tokens.entrySet()) {
    System.out.println(e.getKey() + " has " + e.getValue() + " tokens");
}

tokens.entrySet().forEach(e -> e.setValue(e.getValue() + 10));
System.out.println("setValue writes through: " + tokens);

Output

ava has 60 tokens
ben has 150 tokens
setValue writes through: {ava=70, ben=160}

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Published 2026-07-30