Re: Value types - compatibility with existing “value objects”

Palo Marton palo.marton at
Thu Jan 8 12:03:25 UTC 2015

Thank you for response. I have read that thread. But apart from first few
messages it seems to deal with something else - mutable types.

My idea with rewriting String as value is not about changing meaning of
java.lang.String. That identifier should still mean heap object with
identity, null, etc... The idea is to give a new name for string value,
e.g. java.lang.string (lowercase s), or just "string". So "String" will be
boxed version of "string" and all old pre-value-types code will use only
boxed objects as before and there will be no semantic change. In new code
you will use "string" in most cases, but you can use also "String" in
places where you need it.

>From what I have read there are no plans to support something like that. Am
I right?

Reason why I am asking this is that some time ago I was thinking about
value types in java and how they should be implemented in JVM. My idea
about how to implement it in JVM was somehow different, but it can support
this old-code / new-code compatibility.

On Thu, Jan 8, 2015 at 11:42 AM, Richard Warburton <
richard.warburton at> wrote:

> Hi,
> Will it be possible (within valhalla) to rewrite java String as value type
>> in JDK and use it in all places in JDK where it makes sense? (eg.
>> Class.forName(string), Object.toString(), Integer.parseInt(string). …)
>> Or more general question:
>> There are already plenty of “value objects” in existing java code. In JDK
>> we have, String, File, Point2D,... Also many people have already declared
>> their own class Point { final x,y; } and similar objects. Once we move to
>> value types in java, will it be possible to rewrite these to value types
>> without breaking compatibility with old pre-value-types code? E.g. if I
>> change my Point object to value type in my library, can this new library
>> (jar) still be used in other projects that were written before this
>> change?
>> And without need to recompile those other projects?
> See this thread:
> regards,
>   Richard Warburton
>   @RichardWarburto <>

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