如何从Android手机获取TimeZone？

import java.util.Calendar;
import java.util.TimeZone;

public class MainActivity extends AppCompatActivity {

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

        Calendar calendar = Calendar.getInstance();
        TimeZone timeZone = calendar.getTimeZone();
        String timeZoneId = timeZone.getID();

        Log.d("TimeZone", "TimeZone ID: " + timeZoneId);
    }
}

import android.content.Context;
import android.text.format.DateFormat;

public class MainActivity extends AppCompatActivity {

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

        String timeZoneId = DateFormat.getTimeZone(getApplicationContext()).getID();

        Log.d("TimeZone", "TimeZone ID: " + timeZoneId);
    }
}

import android.app.AlarmManager;
import android.content.Context;

public class MainActivity extends AppCompatActivity {

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

        AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
        String timeZoneId = alarmManager.getTimeZone();

        Log.d("TimeZone", "TimeZone ID: " + timeZoneId);
    }
}