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() 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 ));
}
} |
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)