ConcurrentHashMap keySet() method in Java with Examples
Last Updated :
30 Oct, 2018
The keySet() method of ConcurentHashMap class in Java is used to create a set out of the key elements contained in the hash map. It basically returns a set view of the keys or we can create a new set and store the key elements in them.
Syntax:
ConcurrentHashMap.keySet()
Parameters: The method does not take any parameter.
Return Value: The method returns a set having the keys of the hash map.
Below programs are used to illustrate the working of keySet() Method:
Program 1: Mapping String Values to Integer Keys.
import java.util.*;
import java.util.concurrent.*;
public class ConcurrentHashMapDemo {
public static void main(String[] args)
{
ConcurrentHashMap<Integer, String> hash_map
= new ConcurrentHashMap<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( "The set is: "
+ hash_map.keySet());
}
}
|
Output:
Initial Mappings are: {20=Geeks, 25=Welcomes, 10=Geeks, 30=You, 15=4}
The set is: [20, 25, 10, 30, 15]
Program 2: Mapping Integer Values to String Keys.
import java.util.*;
import java.util.concurrent.*;
public class ConcurrentHashMapDemo {
public static void main(String[] args)
{
ConcurrentHashMap<String, Integer>
hash_map = new ConcurrentHashMap<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( "The set is: "
+ hash_map.keySet());
}
}
|
Output:
Initial Mappings are: {4=15, Geeks=20, You=30, Welcomes=25}
The set is: [4, Geeks, You, Welcomes]
Note: The same operation can be performed with any type of Mappings with variation and combination of different data types.
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