MainActivity and object class for my timer app.

MainActivity.java

package com.alxmjo.simplymindful.ui;

import android.content.Intent;
import android.os.Bundle;
import android.os.CountDownTimer;
import android.preference.PreferenceManager;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;

import com.alxmjo.simplymindful.R;
import com.alxmjo.simplymindful.session.Session;
import com.alxmjo.simplymindful.settings.SettingsActivity;
import com.alxmjo.simplymindful.utilities.AlarmReceiver;
import com.mikhaellopez.circularprogressbar.CircularProgressBar;

import android.widget.ImageButton;
import android.widget.TextView;

import java.util.concurrent.TimeUnit;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";

    // Session and timer
    public Session session;
    private CountDownTimer countDownTimer;

    // Controls
    private boolean isTicking;

    // Views
    private CircularProgressBar circularProgressBar;
    private FloatingActionButton startPauseButton;
    private ImageButton resetButton;
    private TextView prepDigits;
    private TextView mindDigits;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        PreferenceManager.setDefaultValues(this, R.xml.preferences, false);

        // Initialize session
        initializeSession();

        // Initialize views
        circularProgressBar = (CircularProgressBar) findViewById(R.id.circular_progress_bar);
        startPauseButton = (FloatingActionButton) findViewById(R.id.start_pause_button);
        prepDigits = (TextView) findViewById(R.id.preparation_digits);
        mindDigits = (TextView) findViewById(R.id.mindfulness_digits);

        // Set views
        setPrepDigits(session.getPrepRemaining());
        setMindDigits(session.getMindRemaining());
    }

    // ---Session lifecycle methods---

    private void initializeSession() {
        session = new Session(this);
        isTicking = false;
    }

    public void startSession(View v) {
        if (!isTicking) {
            // Runs on play press
            countDownTimer = new CountDownTimer(session.getPrepRemaining() + session.getMindRemaining(), 10) {

                @Override
                public void onTick(long millisUntilFinished) {
                    if (millisUntilFinished > session.getMindRemaining()) {
                        // Preparation timer
                        session.setPrepRemaining(millisUntilFinished - session.getMindRemaining());
                        setPrepDigits(millisUntilFinished - session.getMindRemaining());
                    } else {
                        // Mindfulness timer
                        prepDigits.setVisibility(View.INVISIBLE);
                        session.setMindRemaining(millisUntilFinished);
                        circularProgressBar.setProgress(((session.getMindLength() - millisUntilFinished) / (float) session.getMindLength()) * 100);
                        setMindDigits(millisUntilFinished);
                    }
                }

                @Override
                public void onFinish() {
                    session = null;
                    isTicking = false;
                    circularProgressBar.setProgress(100);
                    initializeSession();
                }
            };
            countDownTimer.start();
            isTicking = true;
            startPauseButton.setImageDrawable(getResources().getDrawable(android.R.drawable.ic_media_pause));

            // Alarm
            AlarmReceiver.scheduleAlarm(this);
        } else {
            // Runs on pause press
            countDownTimer.cancel();
            isTicking = false;
            startPauseButton.setImageDrawable(getResources().getDrawable(android.R.drawable.ic_media_play));
        }
    }

    public void resetSession(View v) {
        // Runs on reset press
        if (countDownTimer != null) {
            countDownTimer.cancel();
        }
        startPauseButton.setImageDrawable(getResources().getDrawable(android.R.drawable.ic_media_play));
        circularProgressBar.setProgress(0);
        prepDigits.setVisibility(View.VISIBLE);
        initializeSession();
        setPrepDigits(session.getPrepRemaining());
        setMindDigits(session.getMindRemaining());
    }

    // ---UI methods---

    public void setPrepDigits(long l) {
        if (l == 0) {
            prepDigits.setVisibility(View.INVISIBLE);
        } else {
            String s = Long.toString(l / 1000);
            prepDigits.setText(s.replaceFirst("^0+(?!$)", ""));
        }
    }

    public void setMindDigits(long l) {
        if (l >= 3600000) {
            String hms = String.format("%02d %02d %02d", TimeUnit.MILLISECONDS.toHours(l),
                    TimeUnit.MILLISECONDS.toMinutes(l) % TimeUnit.HOURS.toMinutes(1),
                    TimeUnit.MILLISECONDS.toSeconds(l) % TimeUnit.MINUTES.toSeconds(1));
            mindDigits.setText(hms.replaceFirst("^0+(?!$)", ""));
        } else if (l < 3600000 && l >= 60000) {
            String ms = String.format("%02d %02d",
                    TimeUnit.MILLISECONDS.toMinutes(l) % TimeUnit.HOURS.toMinutes(1),
                    TimeUnit.MILLISECONDS.toSeconds(l) % TimeUnit.MINUTES.toSeconds(1));
            mindDigits.setText(ms.replaceFirst("^0+(?!$)", ""));
        } else {
            String s = String.format("%02d",
                    TimeUnit.MILLISECONDS.toSeconds(l) % TimeUnit.MINUTES.toSeconds(1));
            mindDigits.setText(s.replaceFirst("^0+(?!$)", ""));
        }
    }

    // ---Menu methods---

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            Intent intent = new Intent(MainActivity.this, SettingsActivity.class);
            startActivity(intent);
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

Session.java

package com.alxmjo.simplymindful.session;

import android.content.Context;
import android.content.SharedPreferences;
import android.preference.PreferenceManager;

public class Session {

    private long prepLength;
    private long mindLength;
    private long prepRemaining;
    private long mindRemaining;

    // Constructor
    public Session(Context context) {
        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
        prepLength = 1000 * Long.parseLong(sharedPreferences.getString("preparation_length", ""));
        mindLength = 60000 * Long.parseLong(sharedPreferences.getString("mindfulness_length", ""));
        prepRemaining = prepLength;
        mindRemaining = mindLength;
    }

    // Getters and setters
    public void setPrepRemaining(long prepRemaining) {
        this.prepRemaining = prepRemaining;
    }
    public long getPrepRemaining() {
        return prepRemaining;
    }

    public void setMindRemaining(long mindRemaining) {
        this.mindRemaining = mindRemaining;
    }
    public long getMindRemaining() {
        return mindRemaining;
    }

    public long getPrepLength() {
        return prepLength;
    }
    public long getMindLength() {
        return mindLength;
    }
}