Re: null terminated strings

[Per Bothner <per@bothner.com>]

Ken Anderson wrote:

 >    In Java, which does copy-on-write

String (including substrings) are immutable, so they cannot be written.
The implementation of the StringBuffer class does do copy-on-write, but
that doesn't affect substrings.

> i often find myself  carefully copying the substrings so they don't share structure.

Why?  The only reason I can think of is garbage collection:  A shared
substring prevents the base from being collected.

> This is because of things like:
> - i don't know how long the underlying string (char array actuall) is.

So?

> Java only has one kind of string, which is fairly heavy weight.  For example, the string "" takes 36 bytes:
> 
>>(describe "")
>  is an instance of java.lang.String
> 
>   // from java.lang.String
>   value: [C@d42d08
>   offset: 0
>   count: 0
>   hash: 0

This depends on the implementation, and the version of the
implementation.

GCJ uses for "":
   object header (4 bytes on 32-but systems)
   private Object data; /* points to itself in this case */
   private int boffset; /* offset of first char within data */
   int count; /* number of character */
   private int cachedHashCode;
   /* chars follow if data==this */
(The data and boffset fields are only accessed by native C++ code.)

Total 20 bytes.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/



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