java - Can't access SharedPreferences in class that extend Application -

i'm trying code global method extending application class. i'm trying add 2 method rapidly access 1 value stored in sharedpreferences. unfortunately can't make sharedpreferences work, here code:

package postfixcalculator.mattiarubini.com.postfixcalculator;  import android.app.application; import android.content.context; import android.content.sharedpreferences;  public class postfixcalculatorextendapplication extends application {      public void changepreference (boolean flag){         //i'm updating preference file based on purchase         sharedpreferences sharedpref = getactivity().getpreferences(context.mode_private);         sharedpreferences.editor editor = sharedpref.edit();         editor.putboolean(getstring(r.string.purchase_status), flag);         editor.commit();     }      public boolean retrievepreferences (){         sharedpreferences sharedpref = this.getpreferences(context.mode_private);         /*if file doesn't exist, create file , i'm returned false value.         * because if file not created it's first install.         * if user acquired product on store, able restore purchase.*/         boolean flagpurchase = sharedpref.getboolean(getstring(r.string.purchase_status), false);         return flagpurchase;     } } 

i understand getactivity() doesn't work in activity in fragment, don't know in specific case. in activity, make sharedpreferences works, need use key word this.

these errors get:

cannot resolve method 'getactivity()'

cannot resolve method 'getpreferences(int)'

try getapplicationcontext() getsharedpreferences()