HashMap containsKey() Method in Java

The java.util.HashMap.containsKey() method is used to check whether a particular key is being mapped into the HashMap or not. It takes the key element as a parameter and returns True if that element is mapped in the map.

Syntax:

Hash_Map.containsKey(key_element)

Parameters: The method takes just one parameter key_element that refers to the key whose mapping is supposed to be checked inside a map.
Return Value: The method returns boolean true if the presence of the key is detected else false .
Below programs are used to illustrate the working of java.util.HashMap.containsKey() Method: 
Program 1: Mapping String Values to Integer Keys. 

Initial Mappings are: {20=Geeks, 25=Welcomes, 10=Geeks, 30=You, 15=4}
Is the key '20' present? true
Is the key '5' present? false

Program 2: Mapping Integer Values to String Keys. 

Initial Mappings are: {4=15, Geeks=20, You=30, Welcomes=25}
Is the key 'Welcomes' present? true
Is the key 'World' present? false

Note: The same operation can be performed with any type of Mappings with variation and combination of different data types.

Time Complexity:

Time Complexity of HashMap.containsKey() is O(1) in Average Case, and O(n) in worst case.