Simplifiable 'Map' operations

Reports common usage patterns of java.util.Map and suggests replacing them with: getOrDefault(), computeIfAbsent(), putIfAbsent(), merge(), or replaceAll().

Example:

map.containsKey(key) ? map.get(key) : "default";

After the quick-fix is applied:

map.getOrDefault(key, "default");

Example:

List<String> list = map.get(key);
if (list == null) {
  list = new ArrayList<>();
  map.put(key, list);
}

After the quick-fix is applied:

map.computeIfAbsent(key, localKey -> new ArrayList<>());

Example:

Integer val = map.get(key);
if (val == null) map.put(key, 1);
else map.put(key, val + 1);

After the quick-fix is applied:

map.merge(key, 1, (localKey, localValue) -> localValue + 1);

Example:

for (Map.Entry<String, String> entry : map.entrySet()) {
  map.put(entry.getKey(), transform(entry.getValue()));
}

After the quick-fix is applied:

map.replaceAll((localKey, localValue) -> transform(localValue));

Note that the replacement with computeIfAbsent() or merge() might work incorrectly for some Map implementations if the code extracted to the lambda expression modifies the same Map. By default, the warning doesn't appear if this code might have side effects. If necessary, enable the Suggest replacement even if lambda may have side effects option to always show the warning.

Also, due to different handling of the null value in old methods like put() and newer methods like computeIfAbsent() or merge(), semantics might change if storing the null value into given Map is important. The inspection won't suggest the replacement when the value is statically known to be nullable, but for values with unknown nullability the replacement is still suggested. In these cases, we recommended suppressing the warning and adding an explanatory comment.

This inspection reports only if the language level of the project or module is 8 or higher.

Inspection options

Option	Type	Default
Suggest conversion to Map.computeIfAbsent	Checkbox	true
Suggest conversion to Map.getOrDefault	Checkbox	true
Suggest conversion to Map.putIfAbsent	Checkbox	true
Suggest conversion to Map.merge	Checkbox	true
Suggest conversion to Map.replaceAll	Checkbox	true
Treat 'get(k) != null' the same as 'containsKey(k)' (may change semantics)	Checkbox	false
Suggest replacement even if lambda may have side effects	Checkbox	false

Inspection Details
Available in:	IntelliJ IDEA 2023.3, Qodana for JVM 2023.3
Plugin:	Java, 233.SNAPSHOT

Last modified: 13 July 2023