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.
// Java code to illustrate the containsKey() methodimport 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));    }} |
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 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"));    }} |
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)
