how can you modify a String?

[christie xu]

According to my teacher, String is like an array, it can not be resized once created. But how come you can modify a String like:
String s = "abc";
s += "-" + "def";
This is confusing me.

[Pat Barrett]

You're actually creating a new String object!
pb

[Marilyn de Queiroz]

You cannot modify a String. Strings are by definition immutable. However, you can assign a new String to the same String reference.

It is perfectly legal to write
String s1 ;
String s2 = "Hello";
s1 = "abc" ;
s1 = "def" ;
s1 = s2 ; // s1 is now a reference to the String "Hello"
s1 = "abc" + s2 ;
s1 += s2 ;

When you finish you will have 2 references (s1 and s2) and 5 Strings:
"Hello"
"abc"
"def"
"abcHello"
"abcHelloHello"

The old Strings don't get changed or go away, they just aren't referenced anymore.

[Johannes de Jong]

Originally posted by Marilyn deQueiroz:
The old Strings don't get changed or go away, they just aren't referenced anymore.

Can you "re-reference" them without assigning the same value again? ie. s1 = "abc"

[Marilyn de Queiroz]

Once the reference to the String has been lost there is no way to recall it.

However, since the String is still there, when you assign a new (identical) String, Java goes to the String pool, pulls it out , and uses it rather than creating a new identical String.

[Johannes de Jong]

Pretty clever, where do you learn all this stuff by the way?
After posting the above I realized that my reply could be misinterpret I meant Java is pretty clever, but dont worry Marilyn I think you are too
[This message has been edited by Johannes de Jong (edited April 24, 2001).]

[Marilyn de Queiroz]

I learned a lot of it in the forums here at JavaRanch (especially about Strings).

[Johannes de Jong]

Maybe time that I started "surfing" in the other Forums too.