Why doesnt this String change?

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SlowLearner - 16 Dec 2006 22:14 GMT

I'm trying to create a method which returns a flag and a string. So I
passed the String as an argument but it doesn't change. I thought all
objects were past as references and so I could change the value. What
am I doing wrong?

SomeEvent(....) {
String FolderName="123";
if (test(FolderName)) Do SomeThing;
// FolderName still 123 at this line. Why isn't it asdfg?
}

public boolean test(String txt) {
txt="asdfg";
return true;
}

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John Ersatznom - 16 Dec 2006 23:12 GMT

> I'm trying to create a method which returns a flag and a string. So I
> passed the String as an argument but it doesn't change. I thought all
[quoted text clipped - 11 lines]
> return true;
> }

The line

txt="asdfg";

is assigning a String object "asdfg" to the reference "txt", but doesn't
change the reference "FolderName". The references themselves aren't
passed by reference. :)

If you invoked a method on txt that altered its contents, it would
affect FolderName. But Java strings are immutable, so this isn't
possible. To do what you want you need StringBuffer:

StringBuffer FolderName = new StringBuffer("123");
...
public Boolean test (StringBuffer txt) {
    txt.delete(0, txt.length());
    txt.append("asdfg");
    return true;
}

FolderName now also points to "asdfg" after test(FolderName) is called.
(On the other hand, "txt = new StringBuffer("asdfg");" wouldn't work. It
would change "txt" to refer to a different StringBuffer, rather than
change the StringBuffer itself.)

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SlowLearner - 18 Dec 2006 20:01 GMT

> I'm trying to create a method which returns a flag and a string. So I
> passed the String as an argument but it doesn't change. I thought all
[quoted text clipped - 11 lines]
> return true;
> }

Thanks for your help everybody

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Why doesnt this String change?

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