java - Android Studio: Passing RadioButtons using Intent ERROR NullPointerException -

i beginner apologize in advance following error when running program:

java.lang.nullpointerexception: attempt invoke virtual method 'int android.widget.radiogroup.getcheckedradiobuttonid()' on null object reference 

here code "quiz"

public class quiz extends activity { button btn; radiogroup rg; radiobutton rb1; radiobutton rb2; radiobutton rb3; radiobutton rb4; 

then below that: 2

and xml "quiz":

<?xml version="1.0" encoding="utf-8"?> <relativelayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent"> <radiogroup     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignparentbottom="true"     android:layout_centerhorizontal="true"     android:id="@+id/rg"> <radiobutton     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:text="option 1"     android:id="@+id/rb1"     android:layout_marginbottom="55dp"     android:layout_above="@+id/rb2"     android:layout_centerhorizontal="true"     android:checked="false" />  <radiobutton     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:text="option 2"     android:id="@+id/rb2"     android:layout_above="@+id/rb3"     android:layout_alignleft="@+id/rb1"     android:layout_alignstart="@+id/rb1"     android:layout_marginbottom="58dp"     android:checked="false" />  <radiobutton     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:text="option 3"     android:id="@+id/rb3"     android:layout_above="@+id/rb4"     android:layout_alignleft="@+id/rb2"     android:layout_alignstart="@+id/rb2"     android:layout_marginbottom="57dp"     android:checked="false" />  <radiobutton     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:text="option 4"     android:id="@+id/rb4"     android:layout_marginbottom="71dp"     android:layout_alignparentbottom="true"     android:layout_alignleft="@+id/rb3"     android:layout_alignstart="@+id/rb3"     android:checked="false" /> </radiogroup> <textview     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:textappearance="?android:attr/textappearancelarge"     android:text="question:"     android:id="@+id/textview3"     android:layout_margintop="39dp"     android:layout_alignparenttop="true"     android:layout_centerhorizontal="true" />  <button     style="?android:attr/buttonstylesmall"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:text="next"     android:id="@+id/nextbtn"     android:layout_alignparentbottom="true"     android:layout_alignparentright="true"     android:layout_alignparentend="true" /> 

second activity (quiz1): 3

any appreciated thank lots <3

radiogroup rg need init step check radiobutton before invoke getcheckedradiobuttonid().

like this:

radiogroup rg; radiobutton rb1; rg = .... rb1 = .... // check radiobutton first rg.check(r.id.rb1); 

and make sure id in "findviewbyid" method similar radiogroup's id in layout xml.