containsValue

ContainsValue is a method defined in the Map interface of the Java standard library. It checks whether the map maps one or more keys to a specified value and returns true if such a mapping exists. The method considers only the values in the map, not the keys.

Signature and behavior: The method is declared as boolean containsValue(Object value). It uses the equals method to compare the provided value with the values stored in the map. If the value is null, the method will return true if the map contains at least one entry with a null value. If no entry has the given value, the method returns false. The method does not indicate which key produced the value; it only reports presence of the value.

Performance and implementation notes: In typical implementations such as HashMap, containsValue performs a linear scan over the map’s entries, resulting in O(n) time complexity, where n is the number of mappings. It generally has O(1) additional space usage beyond the existing map storage. Some specialized map implementations may optimize containsValue, but the contract does not guarantee any constant-time behavior.

Relation to other methods: containsValue is distinct from containsKey, which checks for the presence of a specific key. A map may contain multiple keys that map to the same value. The values() collection can also be used to examine the presence of values, but containsValue provides a direct API-level check.

Example: For a map with entries {"a"->1, "b"->2}, containsValue(2) returns true, while containsValue(3) returns false. If the map stores a null value, containsValue(null) may return true accordingly.