HTTP request with volley Java/Android -

i'm trying make http request page, application aways crash. first java application i'm beginner. been researching while not find solution:

    package com.lookingunique.splashstockcontrol;   import android.app.activity; import android.os.bundle; import android.text.editable; import android.text.textwatcher; import android.view.view; import android.widget.button; import android.widget.edittext; import android.widget.toast; import com.android.volley.request; import com.android.volley.requestqueue; import com.android.volley.response; import com.android.volley.volleyerror; import com.android.volley.toolbox.stringrequest; import com.android.volley.toolbox.volley;   public class mainactivity extends activity {  edittext barcode;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);      barcode = (edittext) findviewbyid(r.id.etbarcode);     final button addbtn = (button) findviewbyid(r.id.button);      addbtn.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {              string barcodeval = barcode.gettext().tostring();             // instantiate requestqueue.             requestqueue queue = volley.newrequestqueue(getapplicationcontext());             string url ="http://xxzx.com/zzz/xzxx/yyy.php?barcode="+ barcodeval +"&action=check";              // request string response provided url.             stringrequest stringrequest = new stringrequest( request.method.get, url,                     new response.listener<string>() {                         @override                         public void onresponse(string response) {                             // display first 500 characters of response string.                             string test = response.substring(0,100);                             toast.maketext(getapplicationcontext(), test, toast.length_short).show();                         }                     }, new response.errorlistener() {                 @override                 public void onerrorresponse(volleyerror error) {                     string test = "that didn't work!";                     toast.maketext(getapplicationcontext(), test, toast.length_short).show();                 }             });             // add request requestqueue.             queue.add(stringrequest);             }     });      barcode.addtextchangedlistener(new textwatcher() {         @override         public void beforetextchanged(charsequence s, int start, int count, int after) {          }          @override         public void ontextchanged(charsequence s, int start, int before, int count) {             addbtn.setenabled(!barcode.gettext().tostring().trim().isempty());         }          @override         public void aftertextchanged(editable s) {          }     }); }   } 

08-25 10:15:15.336 2029-2029/com.lookingunique.splashstockcontrol e/androidruntime﹕ fatal exception: main process: com.lookingunique.splashstockcontrol, pid: 2029 java.lang.stringindexoutofboundsexception: length=0; regionstart=0; regionlength=100 @ java.lang.string.startendandlength(string.java:298) @ java.lang.string.substring(string.java:1087) @ com.lookingunique.splashstockcontrol.mainactivity$1$1.onresponse(mainactivity.java:47) @ com.lookingunique.splashstockcontrol.mainactivity$1$1.onresponse(mainactivity.java:43) @ com.android.volley.toolbox.stringrequest.deliverresponse(stringrequest.java:60) @ com.android.volley.toolbox.stringrequest.deliverresponse(stringrequest.java:30) @ com.android.volley.executordelivery$responsedeliveryrunnable.run(executordelivery.java:99) @ android.os.handler.handlecallback(handler.java:739) @ android.os.handler.dispatchmessage(handler.java:95) @ android.os.looper.loop(looper.java:148) @ android.app.activitythread.main(activitythread.java:5417) @ java.lang.reflect.method.invoke(native method) @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:726) @ com.android.internal.os.zygoteinit.main(zygoteinit.java:616)

it seems request not failing response doesn't contain 100 length string if check documentation substring states that:

throws: indexoutofboundsexception - if beginindex negative, or endindex larger length of string object, or beginindex larger endindex.

try , print string instead