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String is immutable?

At: http://javarevisited.blogspot.com/2010/10/why-string-is-immutable-in-java.html

It says print should have --> B: TEST, A: TEST

But I get --> B: TEST, A: Test

Q1: What am I missing?
Q2: Could you explain why and how String is immutable?

Thank you.

public class StringTest {
    public static void main(String[] args){
        // at: http://javarevisited.blogspot.com/2010/10/why-string-is-immutable-in-java.html
        // it says print line should have-->   B: TEST, A: TEST
        // but I get -->   B: TEST, A: Test
        String A = "Test";
        String B = "Test";
        //System.out.println("B: "+B+", A: "+A+"\n");
        System.out.println("B: "+"Test".toUpperCase()+", A: "+A+"\n");
    }
}

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for_yan

What else can you have:
String A = "Test";
System.out.println("B: "+"Test".toUpperCase()+", A: "+A+"\n");
Of course:
B: TEST,A: Test

for_yan

I ran it - nothing else can be printed - mutable or immutabe:
String A = "Test";
System.out.println("B: "+"Test".toUpperCase()+", A: "+A+"\n");

output:

B: TEST, A: Test

for_yan

They write here: "Imagine" - and how bad it would have been.
Nothing like that happens in fact.
---
1)IMAGINE StringPool facility without making string immutable , its not possible at all because in case of string pool one string object/literal e.g. "Test" has referenced by many reference variables , so if any one of them change the value others will be automatically gets affected i.e. lets say

String A = "Test"
String B = "Test"

Now String B called "Test".toUpperCase() which change the same object into "TEST" , so A will also be "TEST" which is not desirable.
-----

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for_yan

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Mike Eghtebas

ASKER

thanks

for_yan

And immutable jsut means that
when it does
B = B.toUpperCase();

it does not go to every charcater and chnege the particular memory cell
from lower to upper, but rather creates a new String in a new place
with uppercase chracters and then changes tha pointer, so that in our code pointer
associated with B will be now pointing to uppercase string in iits new place
(so our varuiable in the program continues to be B, but teh actual numeric memory address
form this point will in fact be different).
Well, this is of course some simplification relative tio the physical processes with jvm interperting, etc,
but this undderstanding reflect the reality sufficiently well, so that
we could understand what is going on with our string variables
when we are writing java code