String Class is not Immutable

[Ram Pathan]

How can you say that strings are immutable
when you can do an operation like
String motto="Program Once"
motto=motto+"execute everywhere"
motto=motto.concat("dont bet oin it!");
(Plz refer Mughal and rasmussen page 311)

[Thomas Paul]

And everyone of those creates a completely new and distinct object. You haven't created one String object... you have created three!

[Corey McGlone]

Originally posted by Rama Krishna Pathangi:
How can you say that strings are immutable
when you can do an operation like
String motto="Program Once"
motto=motto+"execute everywhere"
motto=motto.concat("dont bet oin it!");
(Plz refer Mughal and rasmussen page 311)

Because none of these operations modify a String object. Rather, each and every one of these creates a brand new String object. Take this example:

String s = "First String";
String t = s;
 
s = s.concat(", Second String");
 
System.out.println(s);
System.out.println(t);

This code snippet generates the following output:

First String, Second String
First String

If the original String object had actually been modified, both variables would have referenced the same String. Rather, when the concat method was invoked, a new String was created and returned from that method.
The String object is, indeed, immutable.
Corey

[Jose Botella]

The methods on String objects that seems to modify them, don't do that. They just create a new String and return it. The original string object is untouched. If you assign the returned string object to the same variable, that variable just point another object. The original string didn't change.
It is the same for the + operator.
Take a look at this code:

public class Test
{   public static void main(String[] args) throws Exception
    {   String motto="Program Once";
        System.out.println(motto.concat("dont bet oin it!"));
        System.out.println(motto);
    }
}
/*
Program Oncedont bet oin it!
Program Once
*/

[Jessica Sant]

Originally posted by Thomas Paul:
And everyone of those creates a completely new and distinct object. You haven't created one String object... you have created three!

Hence the reason why String Concatenation is such an expensive operation.