java - attempt to invoke virtual method on a null object reference using intent to another activity -


in android application, have 2 activity classes. have button on first 1 , want show second when clicked, error. here classes:

public class mainactivity extends activity{     @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);          button startbutton = (button)findviewbyid(r.id.startbtn);         startbutton.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view view) {                 intent intent = new intent(mainactivity.this, startfield.class);                 startactivity(intent);             }         });     } }

here second class: 

public class startfield extends activity {     @override     public void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.start_layout);          button startbutton = (button) findviewbyid(r.id.end);         startbutton.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view view) {                 finish();             }         });     } }

i added second class in manifest file. when press button, error comes , in logcat says 

 caused by: java.lang.nullpointerexception: attempt invoke virtual method 'void android.widget.button.setonclicklistener(android.view.view$onclicklistener)' on null object reference         @ com.example.tavatievs.kurstoti.startfield.oncreate(startfield.java:20)


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