Java avoiding null pointer exception in generic class -


okay here 2 classes.my aim insert in obt using generic class.in case trying strings.when call insert method in main keep getting: 

exception in thread "main" java.lang.nullpointerexception @ obtcomparable.insert(obtcomparable.java:37) @ findtest.main(findtest.java:12)

i found problem: since var "data" null , can't use compare.

the question: how can change "data" avoid null pointer exception(it string).

generic obtcomparable class:

public class obtcomparable<type extends comparable<type>>                          {   private boolean empty;    private type data;   private obtcomparable left;   private obtcomparable right;    public obtcomparable()   {     setempty();   }    private void setempty()   {     empty = true;     data = null;  /////////////////// problem //     left = null;     right = null;   }     private void setdata(type reqdata)   {     if (empty)     {       empty = false;       left = new obtcomparable();       right = new obtcomparable();     }     data = reqdata;   }     public void insert(type insertdata)   {     int compare = data.compareto(insertdata); /////////////// here     if (empty)       setdata(insertdata);     else if (compare < 0)       left.insert(insertdata);     else       right.insert(insertdata);   }      public boolean find(type finddata)   {     int compare = finddata.compareto(data);     if (empty)       return false;     else if (compare == 0)       return true;     else if (compare < 0)       return left.find(finddata);     else       return right.find(finddata);   }        public int compareto(obtcomparable<type> other)        { return 0; }  } // class

test class:

public class test {   public static void main(string[] args)   {     obtcomparable<string> obt = new obtcomparable<string>();     string [] insertstrings =        new string [] { "my", "name", "is", "mark", "smith", "and", "my",                       "hobbies", "include", "films", "music", "computing" };       (int = 0; < insertstrings.length; i++)     {       obt.insert(insertstrings[i]); //////////// here       system.out.println("inserting" + insertstrings[i]);     }   } // main } // class

in method you're referencing data before call setdata you're going problem.

a rewrite of insert around be

public void insert(type insertdata) {     if (empty)      {         setdata(insertdata);     }     else     {         int compare = data.compareto(insertdata);         if (compare < 0)             left.insert(insertdata);         else             right.insert(insertdata);     } }

you need apply similar changes find()

you should @ optional way represent values may null. ideally, state of object set in constructor have valid object immediately.


Comments

Post a Comment

Popular posts from this blog

php - failed to open stream: HTTP request failed! HTTP/1.0 400 Bad Request -

this code i'm using find latitude , longitude of place: function coords($address){ echo $url="http://maps.googleapis.com/maps/api/geocode/json?address=".$address; $json = file_get_contents(urlencode($url)); $data = json_decode($json, true); print_r($data['results'][0]['geometry']['location']['lat']); print_r($data['results'][0]['geometry']['location']['lng']); } however returns warning: failed open stream: http request failed! http/1.0 400 bad request if use above code in simple procedure works fine not in function. note: have tried curl_init()... method produced same result? instead of encoding whole url encode address part. following code work fine $add='jamshoro phase 2'; $url="http://maps.googleapis.com/maps/api/geocode/json?address=".urlencode($add); $json = file_get_contents($url); $data = json_decode($json, true); print_r($data['r
Read more

java - How to filter a backspace keyboard input -

i have code gives message when key number pressed: txtvalueofclause.addeventfilter(keyevent.key_typed, new eventhandler<keyevent>() { @override public void handle(keyevent t) { char ar[] = t.getcharacter().tochararray(); char ch = ar[t.getcharacter().tochararray().length - 1]; if (!(ch >= '0' && ch <= '9')) { system.out.println("the char entered not number"); t.consume(); } } }); now if press on wrong button , press backspace remove it, error message. how can add backspace input if statement? i have found answer: txtvalueofclause.addeventfilter(keyevent.key_typed, new eventhandler<keyevent>() { @override public void handle(keyevent t) { char ar[] = t.getcharacter().tochararray(); char ch = ar[t.getcharacter().tochar
Read more

java - Show Soft Keyboard when EditText Appears -

i have code in android app, alert dialog , keyboard, , when dialog shown want keyboard appear. not , not sure why? here code: final alertdialog.builder alert = new alertdialog.builder(this); alert.settitle("title"); alert.setmessage("message"); final edittext input = new edittext(this); input.setinputtype(inputtype.type_class_number); alert.setview(input); input.setonfocuschangelistener(new view.onfocuschangelistener() { @override public void onfocuschange(view v, boolean hasfocus) { if (hasfocus) { log.i(tag, "in focus"); inputmethodmanager inputmethodmanager = (inputmethodmanager) getsystemservice(context.input_method_service); inputmethodmanager.showsoftinput(input, inputmethodmanager.show_implicit); } } }); but keyboard not appear though edit text in focus, , tell appear why, doesn't come up? thanks in advance.
Read more