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.
Java
// Java code to illustrate the containsKey() methodimport java.util.*;public class Hash_Map_Demo { public static void main(String[] args) { // Creating an empty HashMap HashMap<Integer, String> hash_map = new HashMap<Integer, String>(); // Mapping string values to int keys hash_map.put(10, "Geeks"); hash_map.put(15, "4"); hash_map.put(20, "Geeks"); hash_map.put(25, "Welcomes"); hash_map.put(30, "You"); // Displaying the HashMap System.out.println("Initial Mappings are: " + hash_map); // Checking for the key_element '20' System.out.println("Is the key '20' present? " + hash_map.containsKey(20)); // Checking for the key_element '5' System.out.println("Is the key '5' present? " + hash_map.containsKey(5)); }} |
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.
Java
// Java code to illustrate the containsKey() methodimport java.util.*;public class Hash_Map_Demo { public static void main(String[] args) { // Creating an empty HashMap HashMap<String, Integer> hash_map = new HashMap<String, Integer>(); // Mapping int values to string keys hash_map.put("Geeks", 10); hash_map.put("4", 15); hash_map.put("Geeks", 20); hash_map.put("Welcomes", 25); hash_map.put("You", 30); // Displaying the HashMap System.out.println("Initial Mappings are: " + hash_map); // Checking for the key_element 'Welcomes' System.out.println("Is the key 'Welcomes' present? " + hash_map.containsKey("Welcomes")); // Checking for the key_element 'World' System.out.println("Is the key 'World' present? " + hash_map.containsKey("World")); }} |
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.
