java - NullPointerException on Null Check -


i messed below code cannot able distinguish between 2 code snippets:

string check=null;  if(check!=null && check.isempty()){   system.out.println("get inside"); }

above code works fine , print message.

if(check==null && check.isempty()){   system.out.println("get inside") }

this code throw nullpointerexception.not able distinguish between code please help.

the && operator short-circuit, doesn't evaluate right hand side if it's not necessary. in case, it's necessary:

if(check==null && check.isempty()){   system.out.println("get inside") }

if check null (and that's case), you'll continue check condition after &&, , check.isempty(). since check null, it's null.isempty() nep.

why?

when 2 expressions have && between them, if first 1 false, answer false , other side won't checked, when first true, have continue , check other side know if expression should evaluated true or false.

but when have:

if(check!=null && check.isempty()){      system.out.println("get inside") }

then right side won't reached, since it's redundant check it. got false, , doesn't matter if true or false on right side, result false since and (false && whatever = false). why checking?

this link might you.

(i recommend follow java naming conventions , make variables begin lowercase).


Comments

Post a Comment

Popular posts from this blog

SPSS keyboard combination alters encoding -

my question not have programming practical issue on spss. accident keyword combination cannot remember because did not intend press changed encoding in spss , text in data in different language english shown small boxes. nevertheless, when kind of analysis performed different language text shown in output. does know reason? tried change encoding did not produce result. first, @ edit > options , see whether setting unicode or locale. might fix it. if have text in multiple languages, want unicode. otherwise, may have specific locale set wrong. can change set locale, need know locale want use.
Read more

Add new record to the table by click on the button in Microsoft Access -

in ms access form want implement separate button, adds new record table. in order added button , attached button event: private sub btnaddrec_click() refresh codecontextobject on error resume next docmd.gotorecord , , acnewrec if err.number <> 0 btnaddrec.enabled = false end if end end sub everything ok when open window , click btnaddrec button, problem when first of perform navigation through existed records , after click on button. got runtime error: 2105: «you can't go specified record. may @ end of recordset» . how solve issue, need have ability add new record on click on specific button, no matter, have walked or not walked through records before. thanks. i created simple form field call description (and autonumber) , created button code follows click event. filled number of records , navigated through them, clicked addnewrec button. form navigated new record without issues. able click addnewrec button directly after
Read more

CSS3 Transition to highlight new elements created in JQuery -

i want use css3 color transition apply highlight-fading color effect (yellow transparent) new elements appended markup using jquery. css #content div { background-color:transparent; -moz-transition:background-color 2s; -webkit-transition:background-color 2s; -o-transition:background-color 2s; transition:background-color 2s; } #content div.new { background-color:yellow; } html <div id="content"></div> <a id="add-element" href="#">add new element</a> js $('#add-element').click(function() { var newelement = $('<div class="new">new element</div>'); $('#content').append(newelement); newelement.removeclass('new'); }); when click link, new element created. class "new" (background color yellow) , it's appended html markup. should able remove "new" class trigger background color transition transparent (or whate
Read more