Strings are immutable yet they can be changed ?

[anjanesh]

Hi

Trying to get the hang of Java.

In the String doc, its mentioned :

Strings are constant; their values cannot be changed after they are created. String buffers support mutable strings.

But in that case how come this works ?

String s = "abcde"; System.out.println(s);
s = "12345"; System.out.println(s);

Thanks

[fritz]

because you are not changing the String, you are changing what the 's' reference points to.

in other words, 's' is NOT a String, it is a REFERENCE TO a String. 's' lives on the stack, and the String object containing "abcde" lives in the heap (let's not get into the String pool right now). when you run the line

s= "12345", a new String is created in the heap. 's' is changed to point to it, but the String "abcde" is still hanging around, unchanged.

[anjanesh]

So when s references to 12345, does the string obj containing abcde get deleted from the heap ?

[fritz]

no.

String literals are a special case. whenever you have a double quoted string, it gets created in the string pool. these are not eligible for normal garbage collection.

the details are a little more than you need to know right now, but basically:

Strings are never changed. new strings can be created, and references re-assigned to them.

[anjanesh]

So is this a bad way to go about ?

String s = "abcde"; 
s = "12345"; 
.
.
.
s = "somethingelse";

Is there an more efficient way (in terms of memory) to code this ?