Simple Timer Example in android

Here is the simple example of using timer in Android

public void startTimer() {
    timer = new Timer();
    TimerTask timerTask = new TimerTask() {

        @Override
        public void run() {
            runOnUiThread(new Runnable() {

                @Override
                public void run() {
                    textView.setText(String.format(Locale.getDefault(), "%d", time));
                    if (time > 0)
                        time -= 1;
                    else {
                        textView.setText(R.string.hello_world);
                        btnStart.setChecked(false);
                    }
                }
            });
        }
    };
    timer.scheduleAtFixedRate(timerTask, 0, 1000);
}

Full class
MainActivity.java

package com.guna.testapplication;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.CompoundButton;
import android.widget.TextView;
import android.widget.ToggleButton;

import java.util.Locale;
import java.util.Timer;
import java.util.TimerTask;

public class MainActivity extends AppCompatActivity {

    private int time = 20;
    private Timer timer;
    private TextView textView;
    private ToggleButton btnStart;

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

        textView = findViewById(R.id.textView);
        btnStart = findViewById(R.id.toggleButton);

        btnStart.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                if (isChecked) {
                    time = 20;
                    startTimer();
                } else {
                    timer.cancel();
                    timer.purge();
                    textView.setText(R.string.hello_world);
                }
            }
        });
    }

    public void startTimer() {
        timer = new Timer();
        TimerTask timerTask = new TimerTask() {

            @Override
            public void run() {
                runOnUiThread(new Runnable() {

                    @Override
                    public void run() {
                        textView.setText(String.format(Locale.getDefault(), "%d", time));
                        if (time > 0)
                            time -= 1;
                        else {
                            textView.setText(R.string.hello_world);
                            btnStart.setChecked(false);
                        }
                    }
                });
            }
        };
        timer.scheduleAtFixedRate(timerTask, 0, 1000);
    }
}

And here is the activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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="com.guna.testapplication.MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="2dp"
        android:text="@string/hello_world"
        android:textColor="@color/colorAccent"
        android:textSize="22sp"
        android:textStyle="bold"
        app:layout_constraintBottom_toTopOf="@+id/toggleButton"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_chainStyle="packed" />

    <ToggleButton
        android:id="@+id/toggleButton"
        style="@style/Widget.AppCompat.Button.Borderless"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="2dp"
        android:checked="false"
        android:textOff="@string/start"
        android:textOn="@string/stop"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />
</android.support.constraint.ConstraintLayout>

Screenshot:

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