Java newbie question

They are, however the String object that s points to can be changed.

Strings are immutable meaning any operation on an instance of String returns a new String object. Immutable String class is fundamental to the JVM for security reasons. Its critical to the operation of the String pool, which is an optimization on the JVM memory model around the storing of Strings. Only 1 (immutable) instance of a particular String object exists in the pool and then multiple references to the recurring strings exist throughout your program. This is a memory saving technique since the guys realised Strings were used everywhere. If Strings were mutable this could not happen.

[HTML]s=s.toLowerCase();[/HTML]

this reads assign s(the reference) to location of the new object returned from the method.

the original object s was pointing to will go out of scope and be reclaimed by the gc(if no other reference to this String exists see above)

Dont take my word for it tho, its right here in the API implementation.

http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b27/java/lang/String.java#String.toLowerCase%28java.util.Locale%29

[HTML]
public String toLowerCase(Locale locale) {

...
...
return new String(0, count+resultOffset, result);
}
[/HTML]

TarfHead wrote: »

OK thanks.

I don't understand the answer, but that's to do with me, not you

Strings are immutable, but you are re-assigning the value of s, which is why it works.

ie.

s = s.toLowerCase();

works because you are not actually trying to modify the string. the

.toLowerCase()

method that you are calling returns a new value, which is assigned to the reference variable s