java - Cancel an operation on Toast -

i wrote jsoup html scraping class android project. custom class puts user-inputted zip code constructor, , parse html. works in asynchronous thread main thread. since there no right way deal incorrect zip codes, had check null in particular element, specifically:

        if(doc.select("div.columns").first().text() == null)         {             ((activity) context).runonuithread(new runnable() {                 public void run()                  {                     toast toast = toast.maketext(context, r.string.toast_parse_fail, toast.length_long);                     toast.show();                     return;                 }             });         } 

if particular element null (meaning no such data exists zip code), create toast user. why try wouldn't work in case, because jsoup , java doesn't know whether parse failed or not, since web page still loads fine; only, there no data, crash app nullpointerexception code following it.

despite toast exception handling using .runonuithread, app still crash. there particular methods cancel operations follow null-checking method? know crashing because toast not cancelling operations, , preceding execute following code causes nullpointerexceptions.

posted full pollen constructor.

        public pollen(int zipcode, final context context)         {             this.context = context;             this.zipcode = zipcode;             document doc;              try             {                 // pass address wunderground's website using our inputted zipcode                 doc = jsoup.connect("http://www.wunderground.com/displaypollen.asp?zipcode=" + this.zipcode).get();                  if(doc.select("div.columns").first().text() == null)                 {                     ((activity) context).runonuithread(new runnable() {                         public void run()                          {                             toast toast = toast.maketext(context, r.string.toast_parse_fail, toast.length_long);                             toast.show();                             return;                         }                     });                 }                  // "location" xml                 element location = doc.select("div.columns").first();                 this.location = location.text();                  // "pollen type" xml                 element pollentype = doc.select("div.panel h3").first();                 this.pollentype = pollentype.text();                  simpledateformat format = new simpledateformat("eee mmmm dd, yyyy");                  // add 4 items of pollen , dates                 // respective list                 for(int = 0; < 4; i++)                 {                     element dates = doc.select("td.text-center.even-four").get(i);                     element levels = doc.select("td.levels").get(i);                     try                     {                         pollenmap.put(format.parse(dates.text()), levels.text());                     }                     catch (parseexception e)                     {                         ((activity) context).runonuithread(new runnable() {                             public void run()                              {                                 toast toast = toast.maketext(context, r.string.toast_parse_fail, toast.length_long);                                 toast.show();                                 return;                             }                         });                     }                 }             }             catch (ioexception e)             {                 ((activity) context).runonuithread(new runnable() {                     public void run()                      {                         toast toast = toast.maketext(context, r.string.toast_parse_fail, toast.length_long);                         toast.show();                         return;                     }                 });             }         } 

tl;dr still want toast show - want on-toast, cancel operations follow it, since know if particular toast shows, if code following executes, crash app.

since in try-catch-block, can't throw exception?

public pollen(int zipcode, final context context) {     this.context = context;     this.zipcode = zipcode;     document doc;      try {        // pass address wunderground's website using our inputted zipcode        doc = jsoup.connect("http://www.wunderground.com/displaypollen.asp?zipcode=" + this.zipcode).get();         if(doc.select("div.columns").first().text() == null) {            // oh no! div.colums empty. lets throw exception,            // prevent code below executing.            throw new illegalstateexception("div.columns null");        }         // "location" xml        element location = doc.select("div.columns").first();        this.location = location.text();         // "pollen type" xml        element pollentype = doc.select("div.panel h3").first();        this.pollentype = pollentype.text();         simpledateformat format = new simpledateformat("eee mmmm dd, yyyy");         // add 4 items of pollen , dates        // respective list        for(int = 0; < 4; i++) {            element dates = doc.select("td.text-center.even-four").get(i);            element levels = doc.select("td.levels").get(i);             // removed nested try-catch block            pollenmap.put(format.parse(dates.text()), levels.text());        }     } catch (ioexception e) {         displaytoast(context);     } catch (parseexception e) {         // catch parseexception here instead of nesting try-catch blocks.         displaytoast(context);     } catch (illegalstateexception e) {         // catch illegalstateexception thrown when div.columns null,         // , let user know went wrong.         displaytoast(context);     } }  private void displaytoast(context context) {     ((activity) context).runonuithread(new runnable() {         public void run() {             toast toast = toast.maketext(context, r.string.toast_parse_fail, toast.length_long);             toast.show();         }     }); }