HashMap containsKey() Method in Java
Last Updated :
02 Jun, 2023
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
import java.util.*;
public class Hash_Map_Demo {
public static void main(String[] args)
{
HashMap<Integer, String> hash_map = new HashMap<Integer, String>();
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");
System.out.println("Initial Mappings are: " + hash_map);
System.out.println("Is the key '20' present? " +
hash_map.containsKey( 20 ));
System.out.println("Is the key '5' present? " +
hash_map.containsKey( 5 ));
}
}
|
Output:
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
import java.util.*;
public class Hash_Map_Demo {
public static void main(String[] args)
{
HashMap<String, Integer> hash_map = new HashMap<String, Integer>();
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 );
System.out.println("Initial Mappings are: " + hash_map);
System.out.println("Is the key 'Welcomes' present? " +
hash_map.containsKey("Welcomes"));
System.out.println("Is the key 'World' present? " +
hash_map.containsKey("World"));
}
}
|
Output:
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.
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