Показывает время до начала занятий

MainActivity.java

package com.example.timebutton;

import androidx.appcompat.app.AppCompatActivity;

import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.view.View;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Random;

public class MainActivity extends AppCompatActivity {

    static Random random;

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

        random = new Random();
    }

    public void showTime(View view) throws ParseException {
        //цвет заголовка
        getSupportActionBar().setBackgroundDrawable(new ColorDrawable(Color.rgb
                        (random.nextInt(255),
                        random.nextInt(255),
                        random.nextInt(255))));

        //расчет времени
        SimpleDateFormat format = new SimpleDateFormat("dd.MM.yyyy HH:mm:ss");
        long lessonDate = format.parse("09.04.2022 13:30:00").getTime();
        long difference = lessonDate - System.currentTimeMillis();

        long seconds = difference / 1000 % 60;
        long minutes = difference / (60 * 1000) % 60;
        long hours = difference / (60 * 60 * 1000) % 24;
        long days = difference / (24 * 60 * 60 * 1000);

        //вывод времени
        setTitle(String.format("%d days %02d:%02d:%02d", days, hours, minutes, seconds));
    }
}