immutable or what?

[ryan headley]

Why does the following code compile and run correctly if Strings are immutable and can't be modified?

public class Test
{
public static void main(String args[])
{
String s = "This is a test!";
s = (s + "from java");
System.out.println(s);
}
}

It's been a while since I've been working with just the basics, but apparently I need to...heh
I am running JDK 1.3, Win98.
Thanks

[Bosun Bello]

Ryan, strings are immutable.
What s = (s + "from java") is doing is that it's creating another string and "s" is now referencing that new string, which is "This is a test! from java" it no longer points to "This is a test!".
Bosun

[Mike Curwen]

When you code using the + or +=, the compiler uses the StringBuffer class, and the append() method of that class.

eg:

1 String s = new String("Hello");
2 s+="World";

Line 2 gets translated by the compiler into:
2 s = new StringBuffer(s).append("World).toString();

[This message has been edited by Mike Curwen (edited March 30, 2001).]

[Cindy Glass]

Well . . . the effect is as though you had used an append, that is not necessarily what happens.

15.18.1.2 Optimization of String Concatenation
An implementation may choose to perform conversion and concatenation in one step to avoid creating and then discarding an intermediate String object. To
increase the performance of repeated string concatenation, a Java compiler may use the StringBuffer class or a similar technique to reduce the number of
intermediate String objects that are created by evaluation of an expression.

[ryan headley]

Thanx guys...I was thinking that it would puke, I wasn't thinking that it would just change the reference.
Ryan