How to have UDP Server and Client simultaneously listening for incoming and outgoing packets

I'm trying to implement a simple UDP connection in Java and I want both Client and Server to be both listening for incoming messages and be ready to send messages at the same time.

At the moment, the program is such that the server starts out listening for incoming packets so the client send the first message.

I'd really like to know of a simple way to implement this if possible.

Here's the code for the Client:

class EchoClient 
{
	public static void main( String args[] ) throws Exception 
	{
		System.out.println("\nWelcome to UDP Client");
		System.out.println("---------------------------------------------------");
		
		Scanner sc = new Scanner (System.in);
		
		DatagramSocket socket = new DatagramSocket();
		socket.setSoTimeout(120000);

		while (true)
		{
			//Send
			System.out.print("\nEnter message: ");
			String msg = sc.nextLine();			
			byte[] buffer = msg.getBytes();
			DatagramPacket packetS = new DatagramPacket(buffer,buffer.length,InetAddress.getByName(args[0]),1500);
			socket.send( packetS );
			
			//Receive
			DatagramPacket packetR = new DatagramPacket(new byte[512],512);
			socket.receive( packetR );
			System.out.println( "Alice at: "+new Date()+" "+packetR.getAddress()+":"+packetR.getPort()+"\nSays: "+new String(packetR.getData(),0,packetR.getLength()) );
		}
	}
}

And the code for the Server:

class EchoServer 
{
	public static void main( String args[] ) throws Exception 
	{
		System.out.println("\nWelcome to UDP Server");
		System.out.println("---------------------------------------------------");

		Scanner sc = new Scanner (System.in);
		
		DatagramSocket socket = new DatagramSocket(1500);
	
		//Message loop
		while ( true ) 
		{	
			//Receiving
			DatagramPacket packetR = new DatagramPacket(new byte[512],512);
			socket.receive( packetR );
			System.out.println("Bob at: "+new Date()+" "+packetR.getAddress()+":"+packetR.getPort()+"\nSays: "+new String(packetR.getData(),0,packetR.getLength()) );
	
			//Send
			System.out.print("\nEnter message: ");
			String msg = sc.nextLine();
			byte[] buffer = msg.getBytes();
			DatagramPacket packetS = new DatagramPacket(buffer,buffer.length,packetU.getAddress(),packetU.getPort());
			socket.send( packetS );
		}
	}
}

Hello an eay way for doing that is to have mutltiple thread launched in the main.

class EchoServerClient 
{
    public static void main( String args[] ) throws Exception 
    {
        new Thread(() -> {
            EchoServer.main(args) //You can also rename main by another name
        }).start();
        new Thread(() -> {
            EchoClient.main(args) //You can also rename main by another name
        }).start();
    }
}