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  1. JDK
  2. JDK-8192784

Use Long#parseLong(String, int) in UUID#fromString(String) to avoid unnecessary string concatenation

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      Description

      A DESCRIPTION OF THE REQUEST :
      The current implementation of UUID#fromString(String) is as follows:

      ```
      public static UUID fromString(String name) {
          String[] components = name.split("-");
          if (components.length != 5)
              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 leastSigBits = Long.decode(components[3]).longValue();
          leastSigBits <<= 48;
          leastSigBits |= Long.decode(components[4]).longValue();

          return new UUID(mostSigBits, leastSigBits);
      }
      ```

      To convince Long#decode(String) to parse the string as a hexadecimal value, the method prepends "0x" to be beginning of each element of the `components` array. We could instead use `Long#parseLong(String, int)` and avoid five string concatenations per call to `UUID#fromString(String)`:

      ```
      public static UUID fromString(final String name) {
          String[] components = name.split("-");
          if (components.length != 5)
              throw new IllegalArgumentException("Invalid UUID string: "+name);

          long mostSigBits = Long.parseLong(components[0], 16);
          mostSigBits <<= 16;
          mostSigBits |= Long.parseLong(components[1], 16);
          mostSigBits <<= 16;
          mostSigBits |= Long.parseLong(components[2], 16);

          long leastSigBits = Long.parseLong(components[3], 16);
          leastSigBits <<= 48;
          leastSigBits |= Long.parseLong(components[4], 16);

          return new UUID(mostSigBits, leastSigBits);
      }
      ```

      JUSTIFICATION :
      This approach eliminates five string concatenations per call to `UUID#fromString(String)` and also eliminates some unnecessary unboxing (the calls to `Long#longValue()`). With these changes, jmh shows an improvement in throughput of nearly 50%:

      ```
      Benchmark Mode Cnt Score Error Units
      UuidBenchmark.benchmarkUuidFromString thrpt 40 1544067.340 ± 39521.275 ops/s
      UuidBenchmark.benchmarkUuidFromStringWithRadix thrpt 40 2284632.364 ± 53192.174 ops/s
      ```


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            • Assignee:
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              Reporter:
              webbuggrp Webbug Group
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              • Created:
                Updated: