String Question

[Kay Liew]

Question from MindQ's

11. The statement ...

String s = "Hello" + "Java";

yields the same value for s as ...

String s = "Hello";
String s2= "Java";
s.concat( s2 );

Answer is false ?!? Could that be a mistake or have I mis-understood the question ?

class testStringConcat{
public static void main(String [] args){
String s3 = "Hello" + "Java";
String s = "Hello";
String s2 = "Java";
System.out.println(s.concat(s2));
System.out.println(s3);
}
}

[osman cinar eren]

It really is false. that is about the String class in Java. String objects are IMMUTABLE. that is:

s.concat(s2) creates a new object whose value is equal to s+s2, but as this new object is not referenced by any variable, it is unreachable. On the other hand, the original object referenced by 's' remains unchanged.

You should read on the concept of String.

hope this helps.

[meena latha]

s i do agree....
If u dont create a object reference to the string the content will be lost.
But with StringBuffer it doesnt happens like that.

StringBuffer s= new StringBuffer("welcome");
s.append("here");
System.out.println(s);

output
Welcome here.

[Kay Liew]

I understand that String is immutable. But the question as is the "value" the same and not are they the same or "==",

To me, values mean the final print out which in this case both resulted HelloJava.

Ok, i guess the problem is how one define "value". In this case, I thought it is asking about the final printout and not asking about "==" or equal() .

[Steven Bell]

The final value in the two would not be the same.
You missed one thing in your code.

String s1 = "Hello";
String s2 = "Java";
String s3 = s1 + s2;
 
s1.concat(s2);
 
System.out.println(s1);//prints "Hello"
System.out.println(s3);//prints "HelloJava"
 
String s4 = s1.concat(s2);
 
System.out.println(s4);//prints "HelloJava"

[Kay Liew]

Steven,

If you do not alter my original code.

class testStringConcat{
public static void main(String [] args){
String s3 = "Hello" + "Java";
String s = "Hello";
String s2 = "Java";
System.out.println("One is: " + s.concat(s2));
System.out.println("Two is: " + s3);    
}
}

What is the printout of One and Two ? Now isn't that the "value" the same ?
thx.
k

[Steven Bell]

But the question was 'yields the same value for s'

when you do
System.out.println(s.concat(s2)
you are not printing the value of s, but the value returned by the concat method.

[ankur rathi]

In a very simplle manner :

"Hi ".concat("How are you");

will return ( what you are thinking is right ) :
Hi How are you

but you don't have any reference for this object , so this is immutable .

s.concat(s1) ; // don't think that result of this will be refereed by s ( it happens in StringBuffer , not in String ) .
[ January 27, 2005: Message edited by: rathi ji ]