android app stops working when spinner values are selected -

whats problem in code below? application stops working when click go after selecting "information technology" branch , "1st" semester (as have fed data in information technology (1st sem) branch only.

check out log image - http://postimg.org/image/6h006a15b/

spinner branch, semester; button go; textview branchtext, semtext;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     branch = (spinner) findviewbyid(r.id.spinner1);     semester = (spinner) findviewbyid(r.id.spinner2);     go = (button) findviewbyid(r.id.button1);      arrayadapter adapter = arrayadapter.createfromresource(this,             r.array.branch, android.r.layout.simple_spinner_item);     branch.setadapter(adapter);      arrayadapter adapter1 = arrayadapter.createfromresource(this,             r.array.semester, android.r.layout.simple_spinner_item);     semester.setadapter(adapter1);      branch.setonitemselectedlistener(this);     semester.setonitemselectedlistener(this);     go.setonclicklistener(this);  }  @override public void onclick(view arg0) {     // todo auto-generated method stub     string check = branchtext.gettext().tostring();     string check1 = semtext.gettext().tostring();     if(check.equals("information technology")&&check1.equals("1st"))     {         intent it=new intent(mainactivity.this, it1stsem.class);         startactivity(it);     } }  @override public void onitemselected(adapterview<?> parent, view view, int position,         long id) {     // todo auto-generated method stub     switch (parent.getid())     {     case r.id.spinner1:         branchtext = (textview) view;         toast.maketext(this, branchtext.gettext(), toast.length_short).show();         break;      case r.id.spinner2:         semtext = (textview) view;         toast.maketext(this, semtext.gettext(), toast.length_short).show();         break;     } }  @override public void onnothingselected(adapterview<?> arg0) {     // todo auto-generated method stub  } 

}

//it1stsem.java

public class it1stsem extends listactivity {  string[] data = {"mathematics-i", "physics-i", "chemistry", "engg. mechanics", "electrical science"}; listview l; @override protected void oncreate(bundle savedinstancestate) {     // todo auto-generated method stub     super.oncreate(savedinstancestate);     //setcontentview(r.layout.it1stsem);     l= (listview) findviewbyid(r.id.listview1);     //=getlistview();     arrayadapter<string> adapter = new arrayadapter<string>(this, android.r.layout.simple_list_item_1, data);     l.setadapter(adapter); }  @override protected void onlistitemclick(listview l, view v, int position, long id) {     // todo auto-generated method stub     textview temp = (textview) v;     toast.maketext(this, ""+temp.gettext()+ " "+position, toast.length_short).show(); } 

}

//values - strings.xml

<?xml version="1.0" encoding="utf-8"?> 

<string name="app_name">kiit syllabus</string> <string name="hello_world">hello world!</string> <string name="menu_settings">settings</string>  <string-array name="branch" >     <item >civil</item>     <item >mechanical</item>     <item >automobile</item>     <item >electrical</item>     <item >electronics &amp; tele-communication</item>     <item >computer science</item>     <item >information technology</item>     <item >electronics &amp; electrical</item>     <item >electronics &amp; instrumentation</item> </string-array>  <string-array name="semester">     <item >1st</item>     <item >2nd</item>     <item >3rd</item>     <item >4th</item>     <item >5th</item>     <item >6th</item>     <item >7th</item>     <item >8th</item> </string-array> 

//setcontentview(r.layout.it1stsem);

why did comment out line? think that's why cannot find listview1 , nullpointerexception. try uncommenting line.