Java chat exemple

package com.example.firstapp;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.os.SystemClock;
import android.text.TextUtils;
import android.view.Display;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

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

import java.io.IOException;

import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

public class MainActivity extends AppCompatActivity {
    TextView text;
    EditText input;
    EditText usernameInput;
    EditText serverIp;
    OkHttpClient okhttpClient = new OkHttpClient();
    int messageCount;
    JSONArray newMessages;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        messageCount = 0;
        text = (TextView)findViewById(R.id.text);
        //text.setText("Et cette fois, ça fonctionne !\n");
        input = findViewById(R.id.input);
        usernameInput = findViewById(R.id.usernameInput);
        serverIp = findViewById(R.id.serverIp);
        Display display = getWindowManager().getDefaultDisplay();
        usernameInput.setWidth((int)display.getWidth());
        serverIp.setWidth((int)display.getWidth());
        input.setWidth((int)Math.floor(0.75 * display.getWidth()));
        //Button button = findViewById(R.id.button);
        //button.setOnClickListener(new View.OnClickListener() {OnClick(View v)});

        new Thread(
                new Runnable() {
            public void run() {
                while (true) {
                    getNewMessage();
                    SystemClock.sleep(1000);
                }
            }
        }).start();
    }

    public void OnClick(View v){
        if (TextUtils.isEmpty(input.getText().toString()))
            return;
        String req = "query={\"req\": \"send\", \"username\": \"" +
                (TextUtils.isEmpty(usernameInput.getText().toString()) ? "Anonyme" :
                        usernameInput.getText().toString()) + "\", \"message\": \"" +
                input.getText() + "\"}";
        try{
            Request myGetRequest = new Request.Builder()
                    .url("http://" + serverIp.getText().toString() + "?"+req)
                    .build();
            okhttpClient.newCall(myGetRequest).enqueue(new Callback() {
                @Override
                public void onFailure(Call call, IOException e) {
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            connexionLost();
                            messageCount = 0;
                        }
                    });
                }

                @Override
                public void onResponse(Call call, Response response) throws IOException {
                    final String responseText = response.body().string();
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            input.setText("");
                        }
                    });
                }
            });
        }
        catch (Exception e) {
            connexionLost();
        }
    }

    public void getNewMessage()
    {
        String req = "query={\"req\": \"receive\", \"count\": " + messageCount + "}";
        try {
            Request myGetRequest = new Request.Builder()
                    .url("http://" + serverIp.getText().toString() + "?"+req)
                    .build();
            okhttpClient.newCall(myGetRequest).enqueue(new Callback() {
                @Override
                public void onFailure(Call call, IOException e) {
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            connexionLost();
                            messageCount = 0;
                        }
                    });
                }

                @Override
                public void onResponse(Call call, Response response) throws IOException {
                    final String responseText = response.body().string();
                    try {
                        JSONObject res = new JSONObject(responseText);
                        int tempCount = Integer.parseInt(res.getString("newCount"));
                        messageCount = messageCount > tempCount ? 0 : tempCount;
                        newMessages = (JSONArray) res.get("messages");
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                    runOnUiThread(new Runnable() {

                        @Override
                        public void run() {
                            String tempMessages = "";
                            for (int i=0; i < newMessages.length(); i++) {
                                try {
                                    tempMessages += newMessages.getString(i) + "\n" ;
                                } catch (JSONException e) {
                                    e.printStackTrace();
                                }
                            }
                            if (text.getText() == "Serveur off ou pas de connexion\n")
                                text.setText("");
                            if (messageCount != 0)
                                text.setText(text.getText() + tempMessages);
                            else
                                text.setText("");
                        }
                    });
                }
            });
        }
        catch (Exception e) {
            connexionLost();
        }
    }

    public void connexionLost()
    {
        runOnUiThread(new Runnable() {

            @Override
            public void run() {
                text.setText("Serveur off ou pas de connexion\n");
            }
        });
    }

}