Last Updated : 31 Dec, 2018
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_elementthat 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
// 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));
}
}
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
// 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"));
}
}
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)RetroSearch is an open source project built by @garambo | Open a GitHub Issue
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