Android activity does not run. Here's the code -

while try start activity, not run.

logcat shows following error :

07-25 12:10:46.813: e/androidruntime(797): fatal exception: main 07-25 12:10:46.813: e/androidruntime(797): java.lang.runtimeexception: unable instantiate activity componentinfo{com.example.testingandroid/com.example.testingandroid.dosums}: java.lang.nullpointerexception 

my code :

public class dosums extends activity implements onclicklistener {     public radiobutton r1 = (radiobutton) findviewbyid(r.id.doradiobutton1);     public radiobutton r2 = (radiobutton) findviewbyid(r.id.doradiobutton2);     public radiobutton r3 = (radiobutton) findviewbyid(r.id.doradiobutton3);     public radiobutton r4 = (radiobutton) findviewbyid(r.id.doradiobutton4);      public edittext et = (edittext) findviewbyid(r.id.doedittext1);     //button btnnextscreen = (button) findviewbyid(r.id.button1);      timeanddistancem pen = new timeanddistancem();      public string q, a, finalvalue, scale;     public double fv;      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_do_sums);          objcreator();         //btnnextscreen.setonclicklistener(this);         r1.setonclicklistener(this);         r2.setonclicklistener(this);         r3.setonclicklistener(this);         r4.setonclicklistener(this);     }      @override     public boolean oncreateoptionsmenu(menu menu) {         // inflate menu; adds items action bar if present.         getmenuinflater().inflate(r.menu.do_sums, menu);         return true;     }      public void objcreator() {          pen.timeanddistancem();         // setting question         string q = pen.q;         et.settext("question" + q);         // setting options          // 1. getting options         options ops = new options();         ops.optionscreator(pen.fv, pen.scale);          // 2.assigning options         r1.settext(ops.jradiobutton1);         r2.settext(ops.jradiobutton2);         r3.settext(ops.jradiobutton3);         r4.settext(ops.jradiobutton4);     }      public void radiobuttonaction(radiobutton testradio) {          if (testradio.gettext().tostring().equals(pen.finalvalue)) {             objcreator();         }     }      @override     public void onclick(view arg0) {          switch (arg0.getid()) {         /*case r.id.doradiobutton1:             pen.timeanddistancem();             string q = pen.q;             et.settext("question" + q);             break;*/         case r.id.doradiobutton1:             radiobuttonaction(r1);             break;          case r.id.doradiobutton2:             radiobuttonaction(r2);             break;          case r.id.doradiobutton3:             radiobuttonaction(r3);             break;          case r.id.doradiobutton4:             radiobuttonaction(r4);             break;         }     } } 

you should find views after setting content view activity :

public radiobutton r1; public radiobutton r2; public radiobutton r3; public radiobutton r4; public edittext et;  protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_do_sums);         //here should retreive views ids         r1 = (radiobutton) findviewbyid(r.id.doradiobutton1);         r2 = (radiobutton) findviewbyid(r.id.doradiobutton2);         r3 = (radiobutton) findviewbyid(r.id.doradiobutton3);         r4 = (radiobutton) findviewbyid(r.id.doradiobutton4);         et = (edittext) findviewbyid(r.id.doedittext1);