WAT

Preconditions.java

  /*
   * All recent hotspots (as of 2009) *really* like to have the natural code
   *
   * if (guardExpression) {
   *    throw new BadException(messageExpression);
   * }
   *
   * refactored so that messageExpression is moved to a separate
   * String-returning method.
   *
   * if (guardExpression) {
   *    throw new BadException(badMsg(...));
   * }
   *
   * The alternative natural refactorings into void or Exception-returning
   * methods are much slower.  This is a big deal - we're talking factors of
   * 2-8 in microbenchmarks, not just 10-20%.  (This is a hotspot optimizer
   * bug, which should be fixed, but that's a separate, big project).
   *
   * The coding pattern above is heavily used in java.util, e.g. in ArrayList.
   * There is a RangeCheckMicroBenchmark in the JDK that was used to test this.
   *
   * But the methods in this class want to throw different exceptions,
   * depending on the args, so it appears that this pattern is not directly
   * applicable.  But we can use the ridiculous, devious trick of throwing an
   * exception in the middle of the construction of another exception.
   * Hotspot is fine with that.
   */