android - Use sharedPreference to save account and password -

public class loginactivity extends baseactivity{     private sharedpreferences pref;     private sharedpreferences.editor editor;      private edittext accountedit;      private edittext passwordedit;      private button login;     private checkbox rememberpass;      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.login);         accountedit =(edittext)findviewbyid(r.id.account);         passwordedit = (edittext)findviewbyid(r.id.password);         rememberpass=(checkbox)findviewbyid(r.id.remember_pass);          login = (button)findviewbyid(r.id.login);         editor.putboolean("remember_password",false);         boolean isremember = pref.getboolean("remember_password",false);         if(isremember){             string account = pref.getstring("account", "");             string password =pref.getstring("password", "");             accountedit.settext(account);             passwordedit.settext(password);                      rememberpass.setchecked(true);         }          login.setonclicklistener(new onclicklistener() {              @override             public void onclick(view v) {                 string account =accountedit.gettext().tostring();                 string password = passwordedit.gettext().tostring();                  if (account.equals("admin")&& password.equals("123456"))                  {   editor = pref.edit();                     if(rememberpass.ischecked())                     {                         editor.putboolean("remember_password",true);                         editor.putstring("account",account);                         editor.putstring("password",password);                     }                     else                      {                         editor.clear();                     }                     editor.commit();                      intent intent = new intent(loginactivity.this,mainactivity.class);                     startactivity(intent);                     finish();                 }                  else                  {                     toast.maketext(loginactivity.this,"account password invalid",                             toast.length_long).show();                 }                            }         });       }  } 

i use eclipse code android.i got error in logcat,which nullpointerexception cause "boolean isremember = pref.getboolean("remember_password",false);" don't know why.how use getboolean correctly? in advance.

because pref=null at

boolean isremember = pref.getboolean("remember_password",false); 

initialized before used

sharedpreferences pref= preferencemanager.getdefaultsharedpreferences(loginactivity.this);