android - Not able to access getPreferences method -

i not able access getpreferences method of sharedpreferences interface in method.i used getpreferences method in method logintofacebook gives me error private_mode how can solve problem.

this edited code.

    public class facebookutils {  private static final dialoglistener default_auth_activity_code = null;  private static string app_id = "783826255024540";  public facebook facebook = new facebook(app_id); private asyncfacebookrunner masyncrunner; string filename = "androidsso_data"; private sharedpreferences mprefs; button btnfblogin; button btnfbgetprofile; context mcontext;  public facebookutils() {     // todo auto-generated constructor stub  } public void authorize(activity activity, string[] permissions,         final dialoglistener listener) {     authorize(activity, permissions, default_auth_activity_code); } public facebookutils(context context) {  }   @suppresswarnings("unused") public void logintofacebook() {      sharedpreferences sharedpreferences=mcontext.getsharedpreferences("", context.mode_private);     string access_token = mprefs.getstring("access_token", null);     long expires = mprefs.getlong("access_expires", 0);      if (access_token != null) {         facebook.setaccesstoken(access_token);         btnfblogin.setvisibility(view.invisible);         btnfbgetprofile.setvisibility(view.visible);         log.d("fb sessions", "" + facebook.issessionvalid());     }     if (expires != 0) {         facebook.setaccessexpires(expires);     }     if (!facebook.issessionvalid()) {         facebook.authorize((activity) mcontext,                 new string[] { "email", "publish_stream" },                 new dialoglistener() {                     @override                     public void oncancel() {                     }                     @override                     public void oncomplete(bundle values) {                          sharedpreferences sharedpreferences=mcontext.getsharedpreferences("", context.mode_private);                         editor editor=sharedpreferences.edit();                         editor.putstring("access_token",facebook.getaccesstoken());                         editor.putlong("access_expires",facebook.getaccessexpires());                         editor.commit();                         btnfblogin.setvisibility(view.invisible);                         btnfbgetprofile.setvisibility(view.visible);                     }                     @override                     public void onerror(dialogerror error) {                         // function handle error                     }                     @override                     public void onfacebookerror(facebookerror fberror) {                     }                  });         }   }    public void getprofileinformation() {      masyncrunner.request("me", new requestlistener() {          @override         public void onmalformedurlexception(malformedurlexception e, object state) {             // todo auto-generated method stub          }          @override         public void onioexception(ioexception e, object state) {             // todo auto-generated method stub          }          @override         public void onfilenotfoundexception(filenotfoundexception e, object state) {             // todo auto-generated method stub          }          @override         public void onfacebookerror(facebookerror e, object state) {             // todo auto-generated method stub          }          @override         public void oncomplete(string response, object state) {             // todo auto-generated method stub             log.d("profile", response);             string json = response;             try {                 jsonobject profile = new jsonobject(json);                 final string name = profile.getstring("name");                 final string email = profile.getstring("email");                 runonuithread(new runnable() {                     @override                     public void run() {                         toast.maketext(mcontext, "name: " + name + "\nemail: " + email, toast.length_long).show();                     }                 });             } catch (jsonexception e) {                 e.printstacktrace();             }         }     });   } protected void runonuithread(runnable runnable) {     // todo auto-generated method stub } } 

and logcat error.

12-02 13:31:36.648: e/androidruntime(2524): fatal exception: main 12-02 13:31:36.648: e/androidruntime(2524): process: com.facebook.androidhive, pid: 2524 12-02 13:31:36.648: e/androidruntime(2524): java.lang.nullpointerexception: attempt invoke virtual method 'android.content.sharedpreferences android.content.context.getsharedpreferences(java.lang.string, int)' on null object reference 12-02 13:31:36.648: e/androidruntime(2524):     @ com.facebook.demo.facebookutils.logintofacebook(facebookutils.java:56) 12-02 13:31:36.648: e/androidruntime(2524):     @ com.facebook.demo.androidfacebookconnectactivity$1.onclick(androidfacebookconnectactivity.java:51) 12-02 13:31:36.648: e/androidruntime(2524):     @ android.view.view.performclick(view.java:4756) 12-02 13:31:36.648: e/androidruntime(2524):     @ android.view.view$performclick.run(view.java:19749) 12-02 13:31:36.648: e/androidruntime(2524):     @ android.os.handler.handlecallback(handler.java:739) 12-02 13:31:36.648: e/androidruntime(2524):     @ android.os.handler.dispatchmessage(handler.java:95) 12-02 13:31:36.648: e/androidruntime(2524):     @ android.os.looper.loop(looper.java:135) 12-02 13:31:36.648: e/androidruntime(2524):     @ android.app.activitythread.main(activitythread.java:5221) 12-02 13:31:36.648: e/androidruntime(2524):     @ java.lang.reflect.method.invoke(native method) 12-02 13:31:36.648: e/androidruntime(2524):     @ java.lang.reflect.method.invoke(method.java:372) 12-02 13:31:36.648: e/androidruntime(2524):     @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:899) 12-02 13:31:36.648: e/androidruntime(2524):     @ com.android.internal.os.zygoteinit.main(zygoteinit.java:694)` 

this second activity in called class.

public class androidfacebookconnectactivity extends activity {     private static string app_id = "783826255024540";      private facebook facebook = new facebook(app_id);     private asyncfacebookrunner masyncrunner;     string filename = "androidsso_data";     private sharedpreferences mprefs;     button btnfblogin;     button btnfbgetprofile;     @suppresswarnings("unused")     private facebookutils utils;     context mcontext;     @override     public void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.main);         btnfblogin = (button) findviewbyid(r.id.btn_fblogin);         btnfbgetprofile = (button) findviewbyid(r.id.btn_get_profile);         masyncrunner = new asyncfacebookrunner(facebook);         utils = new facebookutils();         btnfblogin.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view v) {                 log.d("image button", "button clicked");                 utils.logintofacebook(mcontext);             }         });         btnfbgetprofile.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view v) {                 utils.getprofileinformation();             }         });     } 

error related activity? getting null exception in line. string access_token = mprefs.getstring("access_token", null);

you have not initialized variable mprefs. hence error since when try mprefs.getstring("access_token", null); null;

as of have declared statement,

private sharedpreferences mprefs; 

but in-order access have initialize as,

 mprefs = getpreferences(mode_private); 

before try use it.