MainActivity.java handler UI communication

package com.example.saigopinarimeti.helloworld;

import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

public class MainActivity extends AppCompatActivity {


    TextView textView;
    Button fetchDate;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = findViewById(R.id.textview);
        fetchDate = findViewById(R.id.fetchdate);

        fetchDate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                new Thread(runnable).start();
            }
        });
    }

    Handler handler = new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(Message msg) {
            Bundle bundle = msg.getData();
            String date =  bundle.getString("data");

            textView.setText("date is : "+date);
            return false;
        }
    });

    Runnable runnable = new Runnable() {
        @Override
        public void run() {
            Message message = Message.obtain();
            Bundle bundle = new Bundle();
            bundle.putString("data",getCurrentTime());
            message.setData(bundle);

            handler.sendMessage(message);

        }
    };



    private String getCurrentTime() {
        SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss MM/dd/yyyy", Locale.US);
        return dateFormat.format(new Date());
    }

}