Re: Strings...immutable?

Patricia Shanahan <>
Sun, 18 Mar 2007 18:51:36 -0700
John T wrote:

After doing a bit more studying, I've learned that it's the contents of
the string object that are subject to change, not the string itself,
hence the idea/rule that strings are immutable. Is this a correct
interpretation or do I need to go back to the books again?

No, the contents of a String object can never change.

Returning to a program I posted earlier in this thread:

1 public class Concatenate {
2 public static void main(String[] args) {
3 String s = "hello";
4 String x = s;
5 s += "good-bye";
6 System.out.println(x);
7 }
8 }

A reference variable such as s or x is either null, or a pointer to some

At line 3, s is assigned a pointer to the object representing the String
literal "hello".

At line 4, that pointer is copied to x. They now both point to the same

Line 5 is equivalent to 's = s + "good-bye";'. The JVM creates a String
object representing the concatenation of the String object s references
and the one representing "good-bye". s is assigned a pointer to that

The output at line 6 shows the value of the object x references, the
original, unmodified "hello".

No String objects where modified in the course of this program.


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