Maps: replaceAll rewrites every value

replaceAll applies a BiFunction to each entry in place, which is cleaner than iterating the entry set and calling setValue.

Code

Map<String, String> headers = new TreeMap<>();
headers.put("accept", "application/json");
headers.put("host", "javacodinghub.com");

headers.replaceAll((key, value) -> value.toUpperCase());
System.out.println(headers);

Map<String, Integer> prices = new TreeMap<>(Map.of("pen", 100, "book", 250));
prices.replaceAll((item, price) -> price * 2);
System.out.println("doubled: " + prices);

Output

{accept=APPLICATION/JSON, host=JAVACODINGHUB.COM}
doubled: {book=500, pen=200}

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Published 2026-07-30