p5

 activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btn_stop"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#C0CA33"
        android:backgroundTint="#7CB342"
        android:text="Stop"
        android:textAlignment="center"
        android:textAllCaps="true"
        android:textColor="#D81B60"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.463"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.623" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="counter application"
        android:textAlignment="center"
        android:textAllCaps="true"
        android:textColor="#5E35B1"
        android:textSize="34sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.434"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.161" />

    <TextView
        android:id="@+id/lbl_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Counter Value"
        android:textAlignment="center"
        android:textAllCaps="false"
        android:textColor="#D81B60"
        android:textSize="24sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.313" />

    <Button
        android:id="@+id/btn_start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="#C0CA33"
        android:backgroundTint="#7CB342"
        android:text="Start"
        android:textAlignment="center"
        android:textAllCaps="true"
        android:textColor="#D81B60"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.463"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.474" />

</androidx.constraintlayout.widget.ConstraintLayout>

mainactivity.java

package com.example.counterapp;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements
        View.OnClickListener {
    TextView lblCounter;
    Button btnStart,btnStop;
    int counter = 0;
    boolean running = false;

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

        lblCounter = (TextView) findViewById(R.id.lbl_text);
        btnStart = (Button) findViewById(R.id.btn_start);
        btnStop = (Button) findViewById(R.id.btn_stop);
        btnStart.setOnClickListener(this);
        btnStop.setOnClickListener(this);
    }


    @Override
    public void onClick(View v) {
        if(v.equals(btnStart)){
            counter = 0;
            running = true;
            new MyCounter().start();
        } else if (v.equals(btnStop)) {
            running = false;
        }
    }


    Handler handler = new Handler()
    {
        public void handleMessage(Message m)
        {
            lblCounter.setText(String.valueOf(m.what));
        }
    };
    class MyCounter  extends Thread{
        public void run(){
            while(running){
                counter++;
                handler.sendEmptyMessage(counter);
                try{
                    Thread.sleep(1000);
                }
                catch (Exception e){ }
            }
        }
    }
}