Map containsKey() method in Java with Examples

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

Syntax:

boolean 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.Map.containsKey() Method:

Program 1: Mapping String Values to Integer Keys.

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

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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.

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

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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.

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/Map.html#containsKey(java.lang.Object)



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