CopyOnWriteArraySet in Java

// Java Program to demonstrates the 
// working of CopyOnWriteArraySet 
import java.util.concurrent.CopyOnWriteArraySet;

public class Geeks {

    public static void main(String[] args)
    {
        // Create a CopyOnWriteArraySet
        CopyOnWriteArraySet<String> s
            = new CopyOnWriteArraySet<>();

        // Adding elements to the set
        s.add("Geek1");
        s.add("Geek2");
        s.add("Geek3");

        System.out.println("Set: " + s);

        // Creating a thread that reads from the set
        Thread readerThread = new Thread(() -> {
            for (String item : s) {
                System.out.println("Reading: " + item);
            }
        });

        // Creating a thread that modifies the set
        Thread writerThread = new Thread(() -> {
            s.add("Grapes");
            System.out.println("Added Geeks");
        });

        // Start both threads
        readerThread.start();
        writerThread.start();
    }
}

// Java Program to demonstrates the working of
// CopyOnWriteArraySet Class
import java.util.*;
import java.util.concurrent.*;

class Geeks extends Thread {

    static CopyOnWriteArraySet<String> s
        = new CopyOnWriteArraySet<>();

    public void run()
    {

        // Child thread trying to add 
        // new element in the Set object
        s.add("D");
    }
    public static void main(String[] args)
    {

        // Adding elements using add() method
        s.add("A");
        s.add("B");
        s.add("C");

        // We create a child thread that 
        // is going to modify CopyOnWriteArraySet s
        Geeks t = new Geeks();

        // Running the child thread 
        // using start() method
        t.start();

        // Try block to check for exceptions
        try {
            // Waiting for the thread to add the element

            // Join ensures that main thread waits for the
            // child thread to finish
            t.join();
        }

        // Catch block to handle exceptions
        catch (InterruptedException e) {
            System.out.println("Child thread interrupted.");
        }

        System.out.println(
            "Set after child thread modification: " + s);

        // Now we iterate through the CopyOnWriteArraySet
        // and we won't get any exception.
        Iterator<String> itr = s.iterator();

        while (itr.hasNext()) {
            String str = itr.next();
            System.out.println(s);

            if (str.equals("C")) {
                // You cannot remove an element directly
                // using the iterator's remove() So instead
                // we can use remove() method of
                // CopyOnWriteArraySet

                // Removing element C
                s.remove(str);
            }
        }

        System.out.println("Final Set: " + s);
    }
}

// Iterate over a CopyOnWriteArraySet 
import java.util.*;
import java.util.concurrent.*;

class Geeks {

    public static void main(String[] args)
    {
        // Creating an instance of CopyOnWriteArraySet
        CopyOnWriteArraySet<String> s
            = new CopyOnWriteArraySet<>();

        // Adding elements using add() method
        s.add("GeeksforGeeks");

        // Creating an iterator after adding the elements
        Iterator<String> i = s.iterator();

        // Display message
        System.out.println("Set contains:");

        // Printing the contents of the set to the console
        while (i.hasNext()) {
            System.out.println(i.next());
        }

        // Re-initialize the iterator 
        // to start iteration again
        i = s.iterator();

        System.out.println(
            "Set contains after re-iteration:");

        // Printing the elements to the console
        while (i.hasNext()) {
            System.out.println(i.next());
        }
    }
}