What is the signature of a Map method that checks if a key exists in the Map?

Explanation:

The method in the Map interface that checks if a certain key exists is called containsKey. The correct signature for this method is boolean containsKey(Object key). It returns true if the map contains a mapping for the specified key, and false if it does not. This method is very useful for avoiding exceptions that are thrown when trying to access a value using a non-existent key.