java - Getting "Force Close" with my first HelloWorldLogin android code -

i trying learn following lab here https://sites.google.com/site/androidcoursearchive/labs/lab-1

here's code

namegetter.java

public class namegetter extends activity implements onclicklistener {      edittext name;     button submit;      /** called when activity first created. */     @override     public void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         this.setcontentview(r.layout.name_getter);         name = (edittext) this.findviewbyid(r.id.edittext1);         submit = (button) this.findviewbyid(r.id.button1);         submit.setonclicklistener(this);     }      public void onclick(view v) {         string username = name.gettext().tostring();         intent submitintent = new intent(namegetter.this, helloworld.class);         submitintent.putextra("username", username);         this.startactivity(submitintent);     } } 

helloworld.java

public class helloworld extends activity {      /** called when activity first created. */     @override     public void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);          textview tv = (textview) this.findviewbyid(r.id.textviewhello);          bundle name = this.getintent().getextras();          if(name != null) {             string nameentered = name.getstring("username");             if(nameentered != null) {                 tv.settext(nameentered);             } else {                 tv.settext("nameentered null");             }         } else {             tv.settext("name null");         }     } } 

i can enter text edittext box,and when press submit button forced close. logcat says following:

java.lang.runtimeexception: unable start activity componentinfo{com.mypackagerhello.com/com.mypackagerhello.com.helloworld}: java.lang.nullpointerexception`

edit: thank all! this.setcontentview(r.layout.main); line missing helloworld.java.

notice in namegetter activity set content view so:

this.setcontentview(r.layout.name_getter); 

but in helloworld activity haven't done so. add line right after super.oncreate , before findviewbyid. luck!