< Subject Test
import java. util. concurrent.*;
public class Main (

public static void main(String[] args)
ConcurrentHashMap chm = new ConcurrentHashMap ();
chm. put(1, "Welcome");
chm. put(2, "to");
chm. put(3, "Java");
chm. put (4, "World");
chm. putIfAbsent (3, "World");
System. out. println("Elements: "+ chm);
chm. remove (2, "Welcome");
System. out. println("Elements after key 2 is removed: "+chm);
chm. putIfAbsent (3, "Java's");
System. out. println("Add new:,"+chm);
chm. replace(3, "Java", "Java New");
System. out. println("After Replacing: "+ chm);