Activity.java

package net.wes.telnet;

import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    private TcpClient mTcpClient;

    public void OnbConnect(View view) {
        EditText port = findViewById(R.id.editPort);
        EditText IP = findViewById(R.id.editIP);
        String ip = IP.getText().toString();
        String strPort = port.getText().toString();
        int port = Integer.valueOf(strPort);

        new ConnectTask().execute();
    }

    public void OnbDisconnect(View view) {
        mTcpClient.stopClient();
    }

    public void OnbSend(View view) {
        EditText txt2snd = findViewById(R.id.editSend);
        EditText tv = findViewById(R.id.textIO);
        String txt = txt2snd.getText().toString();
        mTcpClient.sendMessage(txt + "\r\n");
        txt2snd.setText("");
        tv.append(">" + txt +"\r\n");
    }

    public class ConnectTask extends AsyncTask<String, String, TcpClient> {

        @Override
        protected TcpClient doInBackground(String... message) {
            //we create a TCPClient object and
            mTcpClient = new TcpClient(new TcpClient.OnMessageReceived() {
                @Override
                //here the messageReceived method is implemented
                public void messageReceived(final String message) {
                    //this method calls the onProgressUpdate
                    //publishProgress(message);
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            EditText text = findViewById(R.id.textIO);
                            text.append(message + "\n");
                        }
                    }, ip, port);

                }
            });
            mTcpClient.run();

            return null;
        }
    }
}