import java.net.MalformedURLException;

import org.json.JSONException;
import org.json.JSONObject;

import io.socket.IOAcknowledge;
import io.socket.IOCallback;
import io.socket.SocketIO;
import io.socket.SocketIOException;

public class BasicExample2 {
	public static void main(String[] args) {
		try {
			new BasicExample2();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public BasicExample2() throws Exception {
		SocketIO socket = new SocketIO("http://127.0.0.1:3001/");
		socket.connect(new IOCallback() {
			@Override
			public void onMessage(JSONObject json, IOAcknowledge ack) {
				try {
					System.out.println("Server said:" + json.toString(2));
				} catch (JSONException e) {
					e.printStackTrace();
				}
			}

			@Override
			public void onMessage(String data, IOAcknowledge ack) {
				System.out.println("Server said: " + data);
			}

			@Override
			public void onError(SocketIOException socketIOException) {
				System.out.println("an Error occured");
				socketIOException.printStackTrace();
			}

			@Override
			public void onDisconnect() {
				System.out.println("Connection terminated.");
			}

			@Override
			public void onConnect() {
				System.out.println("Connection established");
			}

			@Override
			public void on(String event, IOAcknowledge ack, Object... args) {
				System.out.println("Server triggered event '" + event + "'");
			}
		});
		
		socket.send("Hello Server!");
	}
}

import org.json.JSONException;
import org.json.JSONObject;

import io.socket.IOAcknowledge;
import io.socket.IOCallback;
import io.socket.SocketIO;
import io.socket.SocketIOException;

public class BasicExample2 {
	public static void main(String[] args) {
		try {
			new BasicExample2();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public BasicExample2() throws Exception {
		SocketIO socket = new SocketIO("http://127.0.0.1:3001/");
		socket.connect(new IOCallback() {
			@Override
			public void onMessage(JSONObject json, IOAcknowledge ack) {
				try {
					System.out.println("Server said:" + json.toString(2));
				} catch (JSONException e) {
					e.printStackTrace();
				}
			}

			@Override
			public void onMessage(String data, IOAcknowledge ack) {
				System.out.println("Server said: " + data);
			}

			@Override
			public void onError(SocketIOException socketIOException) {
				System.out.println("an Error occured");
				socketIOException.printStackTrace();
			}

			@Override
			public void onDisconnect() {
				System.out.println("Connection terminated.");
			}

			@Override
			public void onConnect() {
				System.out.println("Connection established");
			}

			@Override
			public void on(String event, IOAcknowledge ack, Object... args) {
				System.out.println("Server triggered event '" + event + "'");
			}
		});
		
		socket.send("Hello Server!");
	}
}

remove compile time warning