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

Socket.connect doesn't throw exception in Android -

if put nonsense url no exception thrown , none of rest of code executed not rest of asynctask called method connects. try { socketcliente.connect(new inetsocketaddress("f", port), 2000); } catch (unknownhostexception e) { geterror("host doesn't exist"); return -1; } catch (ioexception e) { geterror("could not connect: host down"); return -1; } add catch statement. catch ( exception e ) { log.d(tag, e.getmessage(),e); toast.maketext(getapplicationcontext(), "unexpected error:" + e.getmessage(), toast.length_long).show(); } this write log , pop toast tell what's going on.
Read more

iphone - How do I keep MDScrollView from truncating my row headers and making my cells look bad? -

Image
here's screenshot show describing: and relevant code: - (nsinteger)spreadview:(mdspreadview *)aspreadview numberofcolumnsinsection:(nsinteger)section{ return self.viewmodel.matrix.width - 1; } - (nsinteger)spreadview:(mdspreadview *)aspreadview numberofrowsinsection:(nsinteger)section{ return self.viewmodel.matrix.height - 1; } -(mdspreadviewcell *)spreadview:(mdspreadview *)aspreadview cellforrowatindexpath:(mdindexpath *)rowpath forcolumnatindexpath:(mdindexpath *)columnpath{ mdspreadviewcell *cell = [aspreadview dequeuereusablecellwithidentifier:@"infocell"]; if (cell == nil){ cell = [[[mdspreadviewcell alloc] initwithstyle:mdspreadviewcellstyledefault reuseidentifier:@"infocell"] autorelease]; } cell.textlabel.text = ((dtvendor *)self.vendors[rowpath.row]).name; return cell; } -(cgfloat)spreadview:(mdspreadview *)aspreadview heightforrowheaderinsection:(nsinteger)rowsection{ return 200; } -(cgfloat)spreadview:(mdspreadview...
Read more