asked on

Simple Java question

Why does ..

String password = "bingo";

if ( args[0] == password) not work yet

if( "bingo" == password) does?

PS I am entering the word "bingo" in as a run time parameter
PPS I know I can use args[0].equals(password), I'm just curious why '==' doesn't work in this case.

Mick Barry

== tests for object equality
you needs to equals() method to test object equality

the fact that bingo works is just coincidence that that are the same object (due to string pooling)

CEHJ

That will be because (when it works) the string is drawn from the constant pool and is the same in each case. i.e. it has the same reference. So both

password.equals("bingo")

and

password == "bingo"

are true

sciuriware

if( "bingo" == password)

NEVER DO THAT:

if(password.equals("bingo"))
{
..................

See why?

;JOOP!

SOLUTION

Mick Barry

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sciuriware

>>> if( "bingo" == password) :::

::: "IF THE MEMORY ADDRESS OF THIS LITERAL IS THE SAME AS THAT OF 'password'".

But, you want to know if the content of password is equal to "bingo".

;JOOP!

sciuriware

O what are you guys quick this day.
I was still typing when ........................

;JOOP!

SOLUTION

CEHJ

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me_patrick

ASKER

Wow ... thanks for all the responses. Let me see if I'm getting this ...

String a = "abc", b="abc", c="123";

.... each of these variables are all part of this particular instance of the String Class therefor they would all evaluate as true when compared with ('==') each other .... is that correct?

Secondly, on reading Jim's blog...

final String s1 = j;
final String s2 = im;
String jim = jim;
System.out.println(s1+s2 == jim); // returns true: Constant expression.

String s3 = j;
String s4 = im;
System.out.println(s3 + s4 == jim); // returns false: Not a constant expression.

Is this just very subtle or is it a typo - these comparisons look identical to me, what am I missing?

Thanks again.
Patrick.

PS I'm not up on these texting shortened phrases ... what does ;JOOP! mean?

ASKER CERTIFIED SOLUTION

sciuriware

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sciuriware

.............................. and JOOP is my first name.

;JOOP!

me_patrick

ASKER

Thanks guys for your contributions - I'm finding this quite tricky to get my head around but you given me enough ideas to go away and have a think.

PS. Sorry about the name blunder Joop.

CEHJ

me_patrick: out of interest, from which application did you post the code at http:#23496305 ?

me_patrick

ASKER

Do you mean ...

final String s1 = j;
final String s2 = im;....... etc?

That was cut and pasted from the Jim Blog article you suggested.

Regards.
Patrick

CEHJ

Thanks. The quotes are broken in my browser for this site. They're fine from the original

vahana

Very good link , When u pass string as args it create new String and add it to String array , I think that why
"==" operator compare to different obj