java - Unexpected Crash Android Sensors -

whenever try run crashes. not know problem be. missing or in wrong place?in logcat says system services not avaliable activities before oncreate.

import android.os.bundle; import android.app.activity; import android.hardware.sensor; import android.hardware.sensorevent; import android.hardware.sensoreventlistener; import android.hardware.sensormanager; import android.os.handler; import android.view.menu; import android.widget.*; import android.*;  import java.math.*; import java.text.*; import java.util.*;  public class mainactivity extends activity implements sensoreventlistener {       private final sensormanager msensormanager;     private final sensor mrotationvector;      public float x,y,z;      public mainactivity(){             msensormanager = (sensormanager)getsystemservice(sensor_service);             mrotationvector = msensormanager.getdefaultsensor(sensor.type_rotation_vector);     }      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);     }       protected void onresume() {         super.onresume();         msensormanager.registerlistener(this, mrotationvector, sensormanager.sensor_delay_game);     }      protected void onpause() {         super.onpause();         msensormanager.unregisterlistener(this);     }      @override     public boolean oncreateoptionsmenu(menu menu) {         // inflate menu; adds items action bar if present.         getmenuinflater().inflate(r.menu.main, menu);         return true;     }      @override     public void onaccuracychanged(sensor sensor, int accuracy) {         // todo auto-generated method stub      }      @override     public void onsensorchanged(sensorevent event) {         x= event.values[0];         y= event.values[1];         z= event.values[2];          textview mtextview0 = (textview) findviewbyid(r.id.textview0);         mtextview0.settext("x"+x);         textview mtextview1 = (textview) findviewbyid(r.id.textview1);         mtextview1.settext("y"+y);         textview mtextview2 = (textview) findviewbyid(r.id.textview2);         mtextview2.settext("z"+z);       }  } 

system services not avaliable activities before oncreate 

your logcat telling !

so change

@override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     msensormanager = (sensormanager)getsystemservice(sensor_service);     mrotationvector = msensormanager.getdefaultsensor(sensor.type_rotation_vector); } 

and remove constructor public mainactivity().