求教，Android开发，运行一直显示出错

java代码如下
import java.util.Calendar;
import android.app.Activity;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.app.Service;
import android.app.TimePickerDialog;
import android.app.TimePickerDialog.OnTimeSetListener;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TimePicker;
import android.widget.Toast;
public class MainActivity extends Activity {
AlarmManager aManager;
Calendar currentTime = Calendar.getInstance();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
AlarmManager alarmManager =(AlarmManager) getSystemService(Service.ALARM_SERVICE);
Button setTime =(Button) findViewById(R.id.setTime);
setTime.setOnClickListener(new OnClickListener() {
int hour,sminute;
@Override
public void onClick(View source) {
// TODO Auto-generated method stub
Calendar currentTime=Calendar.getInstance();
new TimePickerDialog(MainActivity.this, 0,new TimePickerDialog.OnTimeSetListener() {
@Override
public void onTimeSet(TimePicker tp, int hourOfDay, int minute) {
// TODO Auto-generated method stub
hour=hourOfDay;
sminute=minute;
Intent intent = new Intent(MainActivity.this,AlarmActivity.class);
PendingIntent pi = PendingIntent.getActivity(MainActivity.this, 0, intent, 0);
Calendar c =Calendar.getInstance();
c.setTimeInMillis(System.currentTimeMillis());
c.set(Calendar.HOUR,hourOfDay);
c.set(Calendar.MINUTE,minute);
aManager.set(AlarmManager.RTC_WAKEUP, c.getTimeInMillis(),pi);这行一直显示出错
Toast.makeText(MainActivity.this,"闹铃设置成功" , Toast.LENGTH_SHORT).show();
}
},currentTime.get(Calendar.HOUR_OF_DAY),currentTime.get(Calendar.MINUTE),false).show();
}
});
}
}