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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);