Hi Robert;
As mentioned in another thread with Steven Schlansker there is a patch in
progress with similar goals. I will look at your patch and see how much overlap
there is and merge in any relevant parts. This improvement won't make it into
Java 8 but will be implemented early in the Java 9 lifecycle and can be
backported to Java 8 updates.
Thanks!
Mike
On Nov 6 2013, at 17:19 , Robert Stupp <sn...@gmx.de> wrote:
> Hi,
>
> the current implementation of java.util.UUID.fromName() and
> java.util.UUID.toString() unnecessarily produce a lot of temporary objects.
> Especially the fromName() method creates some instances of java.lang.Long and
> indirectly via "name.split()" many Strings, an ArrayList, etc.
> UUID.toString() creates at least 10 String objects plus the implicitly
> created char[] instances.
>
> Here's a hg diff which reduces the temporary object count while still
> providing the same functionality.
>
> -
> Robert
>
>
>
>
> diff --git a/src/share/classes/java/util/UUID.java
> b/src/share/classes/java/util/UUID.java
> --- a/src/share/classes/java/util/UUID.java
> +++ b/src/share/classes/java/util/UUID.java
> @@ -189,23 +189,68 @@
> *
> */
> public static UUID fromString(String name) {
> - String[] components = name.split("-");
> - if (components.length != 5)
> + if (name.length() != 36)
> throw new IllegalArgumentException("Invalid UUID string: "+name);
> - for (int i=0; i<5; i++)
> - components[i] = "0x"+components[i];
>
> - long mostSigBits = Long.decode(components[0]).longValue();
> - mostSigBits <<= 16;
> - mostSigBits |= Long.decode(components[1]).longValue();
> - mostSigBits <<= 16;
> - mostSigBits |= Long.decode(components[2]).longValue();
> + long lo;
> + long hi;
> + lo = hi = 0;
>
> - long leastSigBits = Long.decode(components[3]).longValue();
> - leastSigBits <<= 48;
> - leastSigBits |= Long.decode(components[4]).longValue();
> + for (int i = 0, j = 0; i < 36; ++j) {
> + // Need to bypass hyphens:
>
> - return new UUID(mostSigBits, leastSigBits);
> + switch (i) {
> + case 8:
> + case 13:
> + case 18:
> + case 23:
> + if (name.charAt(i) != '-')
> + throw new IllegalArgumentException("Invalid UUID
> string: "+name);
> +
> + ++i;
> + } // switch
> +
> + int curr;
> + char c = name.charAt(i);
> +
> + if (c >= '0' && c <= '9')
> + curr = (c - '0');
> +
> + else if (c >= 'a' && c <= 'f')
> + curr = (c - 'a' + 10);
> +
> + else if (c >= 'A' && c <= 'F')
> + curr = (c - 'A' + 10);
> +
> + else
> + throw new IllegalArgumentException("Invalid UUID string:
> "+name);
> +
> + curr <<= 4;
> +
> + c = name.charAt(++i);
> +
> + if (c >= '0' && c <= '9')
> + curr |= (c - '0');
> +
> + else if (c >= 'a' && c <= 'f')
> + curr |= (c - 'a' + 10);
> +
> + else if (c >= 'A' && c <= 'F')
> + curr |= (c - 'A' + 10);
> +
> + else
> + throw new IllegalArgumentException("Invalid UUID string:
> "+name);
> +
> + if (j < 8)
> + hi = (hi << 8) | curr;
> +
> + else
> + lo = (lo << 8) | curr;
> +
> + ++i;
> + } // for
> +
> + return new UUID(hi, lo);
> }
>
> // Field Accessor Methods
> @@ -373,17 +418,27 @@
> * @return A string representation of this {@code UUID}
> */
> public String toString() {
> - return (digits(mostSigBits >> 32, 8) + "-" +
> - digits(mostSigBits >> 16, 4) + "-" +
> - digits(mostSigBits, 4) + "-" +
> - digits(leastSigBits >> 48, 4) + "-" +
> - digits(leastSigBits, 12));
> + char[] arr = new char[36];
> + arr[8] = arr[13] = arr[18] = arr[23] = '-';
> + long msb = mostSigBits;
> + long lsb = leastSigBits;
> + // upper 32 bit of MSB
> + digits(msb >> 32, 8, arr, 0);
> + // upper 16 bit of lower 32 bit of MSB
> + digits(msb >> 16, 4, arr, 9);
> + // lower 16 bit of lower 32 bit of MSB
> + digits(msb, 4, arr, 14);
> + // upper 16 bit of LSB
> + digits(lsb, 4, arr, 19);
> + // lower 48 bit of LSB
> + digits(lsb, 12, arr, 24);
> + return new String(arr);
> }
>
> - /** Returns val represented by the specified number of hex digits. */
> - private static String digits(long val, int digits) {
> - long hi = 1L << (digits * 4);
> - return Long.toHexString(hi | (val & (hi - 1))).substring(1);
> + private static final char[] HEX =
> {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};
> + private void digits(long v, int digits, char[] arr, int off) {
> + for ( ; digits > 0 ; off++ )
> + arr[off] = HEX[ (int)(v&15) ];
> }
>
> /**
>
>
