android - custom class method access -

i have problem accessing custom class methods handles loads , saves. while same class methods worked intend. since decided reuse save/load methods couple of times needed them in separate class, when try access method program crashes, have solution explanation why? maybe problem mode_private tried changing , still crashes

package com.main.kanji_sama;  import android.app.activity; import android.content.intent; import android.os.bundle; import android.view.view; import android.view.view.onclicklistener; import android.widget.button; import android.widget.checkbox;  import com.main.customclass.sharedpreferences;  public class hiragana extends activity implements onclicklistener{      checkbox cb1,cb2;     button backbutton;     sharedpreferences myfunction = new sharedpreferences();       @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_hiragana);           cb1 = (checkbox) findviewbyid(r.id.hiragana_xx_check);         cb1.setchecked(myfunction.loadsharedpref("cb1"));         cb2 = (checkbox) findviewbyid(r.id.hiragana_kx_check);         cb2.setchecked(myfunction.loadsharedpref("cb2"));          backbutton = (button) findviewbyid(r.id.hiraganaconfbutton);         backbutton.setonclicklistener(this);     }     @override     public void onclick(view v){         startactivity(new intent(hiragana.this, main.class));        }     public void oncheckboxclicked(view view) {     boolean checked = ((checkbox) view).ischecked();     switch(view.getid()) {         case r.id.hiragana_xx_check:             myfunction.savesharedpref("cb1",checked);         break;           case r.id.hiragana_kx_check:             myfunction.savesharedpref("cb2", checked);      } } } **this class**  public class sharedpreferences extends activity {      public boolean loadsharedpref(string key){         sharedpreferences preferences = getapplicationcontext().getsharedpreferences("kanji-sama", android.content.context.mode_private);         return preferences.getboolean(key, false);         }     public void savesharedpref(string key,boolean value){         sharedpreferences preferences = getapplicationcontext().getsharedpreferences("kanji-sama", android.content.context.mode_private);         sharedpreferences.editor editor = preferences.edit();         editor.putboolean(key, value);         editor.commit();         } } 

you no need take class , no need of extend activity.change code this.

public class hiragana extends activity implements onclicklistener {  checkbox cb1, cb2; button backbutton;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_hiragana);      cb1 = (checkbox) findviewbyid(r.id.hiragana_xx_check);     cb1.setchecked(myfunction.loadsharedpref("cb1"));     cb2 = (checkbox) findviewbyid(r.id.hiragana_kx_check);     cb2.setchecked(myfunction.loadsharedpref("cb2"));      backbutton = (button) findviewbyid(r.id.hiraganaconfbutton);     backbutton.setonclicklistener(this); }  @override public void onclick(view v) {     startactivity(new intent(hiragana.this, main.class)); }  public void oncheckboxclicked(view view) {     boolean checked = ((checkbox) view).ischecked();     switch (view.getid()) {     case r.id.hiragana_xx_check:         savesharedpref("cb1", checked);         break;     case r.id.hiragana_kx_check:         savesharedpref("cb2", checked);      } }  public boolean loadsharedpref(string key) {     sharedpreferences preferences = getapplicationcontext()             .getsharedpreferences("kanji-sama",                     android.content.context.mode_private);     return preferences.getboolean(key, false); }  public void savesharedpref(string key, boolean value) {     sharedpreferences preferences = getapplicationcontext()             .getsharedpreferences("kanji-sama",                     android.content.context.mode_private);     sharedpreferences.editor editor = preferences.edit();     editor.putboolean(key, value);     editor.commit(); } } 

that need write oncheckedchange listener checkbox.