String concatenation

[levani dvalishvili]

String name = "levan";
System.out.println("My name is "+name!=null?name:"Not specified");

output is : "Levan"
not : "My name is Levan"
I am wondering why is string concatenation happens before comparison?

[Joshua Smith]

This will give you the expected output, but I'm a little confused how the compiler is understanding the other code that you posted.

String name = "levan";
System.out.println("My name is "+((name!=null)?name:"Not specified"));

I suppose the comparison that it's doing is:
"My name is levan" != null

which evaluates to true and so it prints name.

Josh
[ February 01, 2006: Message edited by: Joshua Smith ]

[Kotto Bass]

Exactly. String concatenation operator has a higher precedence than 'not equal to' operator.

[levani dvalishvili]

yes , I realized putting a parens around solves the problem, but look at this example then :

String name = "hello";
System.out.println(name=null==null?name:"Not specified");
Output is : hello

here comparison happens first and then assignment.
even without parens, I would asume name would be assigned a null value first then comparison and output would be null.

???
getting confused about precedence order
[ February 02, 2006: Message edited by: levani dvalishvili ]

[Keith Lynn]

Originally posted by levani dvalishvili:
yes , I realized putting a parens around solves the problem, but look at this example then :

String name = "hello";
System.out.println(name=null==null?name:"Not specified");
Output is : hello

here comparison happens first and then assignment.
even without parens, I would asume name would be assigned null first then comparison and output would be null.

???
getting confused about precedence order

[ February 02, 2006: Message edited by: levani dvalishvili ]

Why would name be set to null. You are comparing null to null and if they are the same, name is assigned to the value of name. name isn't assigned to null.

[Keith Lynn]

Remember that the ternary operator has higher precedence than the assignment operator.

[levani dvalishvili]

I think yo miss understood :

example 1 :

String name = "levan";
System.out.println("My name is "+name!=null?name:"Not specified");

String concatination happens first,I undertand because concatination(which behind the scene yelds to assignment) has higher precendence than comparison, so
output is : "Levan"

example 2

String name = "hello";
System.out.println(name=null==null?name:"Not specified");

here seems like comparizon happens first and asignment second.
Output is : hello


and if ternary operators have higher precedence than asignment, why output is "levan" in first example? since

"My name is "+name

is type of asignment , right? internaly it means something like

someIternalbuffer.apend("My name is ");
someIternalbuffer.apend(name);
someIternalbuffer.toString();

thats what I am asking.
[ February 02, 2006: Message edited by: levani dvalishvili ]

[Alex Khvatov]

I think you, guys should check out this JavaOne multimedia presentation:

Yet More Programming Puzzlers: TS-3738, 2005
http://developers.sun.com/learning/javaoneonline/2005/coreplatform/TS-3738.html

They explain this problem very well.
Alex