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).