public class MainActivity extends AppCompatActivity {

private int mScore1=0;
private int mScore2=0;
private TextView mScoreText1,mScoreText2;

private static final String STATE_SCORE_1 = "Team score 1";
public static final String STATE_SCORE_2 = "Team score 2";

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

    mScoreText1 = findViewById(R.id.score_1);
    mScoreText2 = findViewById(R.id.score_2);

    // restore score if there is one

    if (savedInstanceState!=null){
        mScore1 = savedInstanceState.getInt(STATE_SCORE_1);
        mScore2 = savedInstanceState.getInt(STATE_SCORE_2);

        mScoreText1.setText(String.valueOf(mScore1));
        mScoreText2.setText(String.valueOf(mScore2));
    }


}

public void increaseScore(View view) {
    int viewId = view.getId();
    switch (viewId){
        case R.id.increaseTeam1:
            mScore1++;
            mScoreText1.setText(String.valueOf(mScore1));
            break;

        case R.id.increaseTeam2:
            mScore2++;
            mScoreText2.setText(String.valueOf(mScore2));
            break;
    }
}

public void decreaseScore(View view) {

    int viewId = view.getId();
    switch (viewId){
        case R.id.decreaseTeam1:
            mScore1--;
            mScoreText1.setText(String.valueOf(mScore1));
            break;

        case R.id.decreaseTeam2:
            mScore2--;
            mScoreText2.setText(String.valueOf(mScore2));
            break;

    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main_menu,menu);
    int nightMode = AppCompatDelegate.getDefaultNightMode();
    if (nightMode==AppCompatDelegate.MODE_NIGHT_YES){
        menu.findItem(R.id.night_mode).setTitle(R.string.day_mode);
    }
    else {
        menu.findItem(R.id.night_mode).setTitle(R.string.night_mode);
    }
    return true;

}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if (item.getItemId()==R.id.night_mode){
        int nightMode = AppCompatDelegate.getDefaultNightMode();
        if (nightMode==AppCompatDelegate.MODE_NIGHT_YES){
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO);
        }
        else {
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);
        }
        recreate();
        return true;
    }
    return super.onOptionsItemSelected(item);
}

@Override
public void onSaveInstanceState(Bundle outState) {
    outState.putInt(STATE_SCORE_1,mScore1);
    outState.putInt(STATE_SCORE_2,mScore2);
    super.onSaveInstanceState(outState);
}
}