RFR: 8357289: Break down the String constructor into smaller methods [v3]

[Per Minborg]

On Sun, 25 May 2025 12:54:03 GMT, Chen Liang <liach at openjdk.org> wrote:

>> private String(char[] value, int off, int len, Void sig) {
>>         if (len == 0) {
>>             this.value = "".value;
>>             this.coder = "".coder;
>>             return;
>>         }
>>         if (COMPACT_STRINGS) {
>>             byte[] val = StringUTF16.compress(value, off, len);
>>             this.coder = StringUTF16.coderFromArrayLen(val, len);
>>             this.value = val;
>>             return;
>>         }
>>         this.coder = UTF16;
>>         this.value = StringUTF16.toBytes(value, off, len);
>>     }
>> 
>> 
>> This constructor has additional processing logic for len == 0. 
>> 
>> ValueObject may be used here in the future. I think it is better to keep the original structure.
>
> I thought this would both increase cleaniness and reduce code size of the decode method. @minborg What do you think? This also removes one of the switches on COMPACT_STRING.

I think it is better to keep the code smaller rather than saving 0.2 ns for skipping the zero-length check, which might get optimized away anyhow.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/25290#discussion_r2107187594