What is Immutable in String

[elektronika]

Dear All,

I learn in the Sun java tutorial, there was something like this :

Note: The String class is immutable, so that once it is created a String object cannot be changed. The String class has a number of methods, some of which will be discussed below, that appear to modify strings. Since strings are immutable, what these methods really do is create and return a new string that contains the result of the operation.

What does it mean by immutable? The contents of the string can easily be changed.

String newstrings;
newstrings = " What do you mean";
System.out.println(newstrings);
newstrings = " With that?";
System.out.println(newstrings);

 What do you mean
 With that?

Kindest Regards,




Elektronika

[masijade]

No, that is not changing the contents of the String. That is changing the Object that the reference variable points to. A String is immutable in that you cannot change the contents of a String object, it has nothing to do with changing the value of a reference.

[elektronika]

Dear masijade,

So what does the

so that once it is created a String object cannot be changed

means?

so before it is created it can be changed? and what does the changed here means...

Kindest Regards,




Elektronika

[masijade]

A String is an object that "wraps" a character array. What is "immutable" about a String is that you cannot change those contents. A variable is not a String. A variable is simply a placeholder in which a pointer to a String can be saved. Changing that pointer does not change the String, it simply changes which String the variable now points to. And before it is created there is nothing to change, of course.

See http://www.javaranch.com/campfire/StoryCups.jsp and http://www.javaranch.com/campfire/StoryPassBy.jsp

[elektronika]

Oh..thank you masijade!
I also found your link useful :)

Kindest Regards,




Elektronika