Maps: getOrDefault avoids a null check

getOrDefault returns a fallback when the key is missing, but it does not insert anything - use putIfAbsent or computeIfAbsent when you want the map changed.

Code

Map<String, Integer> stock = new TreeMap<>(Map.of("pen", 12, "book", 3));

System.out.println("pen   = " + stock.getOrDefault("pen", 0));
System.out.println("mug   = " + stock.getOrDefault("mug", 0));
System.out.println("map unchanged: " + stock);

stock.putIfAbsent("mug", 0);
stock.putIfAbsent("pen", 999);
System.out.println("after putIfAbsent: " + stock);

Output

pen   = 12
mug   = 0
map unchanged: {book=3, pen=12}
after putIfAbsent: {book=3, mug=0, pen=12}

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Published 2026-07-30