Page History

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Because DateFormat is not thread-safe [API 2011], the value for Date returned by the parse() method might fail to correspond to the str argument:

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This compliant solution creates and returns a new DateFormat instance for each invocation of the parse() method [API 2011]:

final class DateHandler {
  public static java.util.Date parse(String str) throws ParseException {
    return DateFormat.getDateInstance(DateFormat.MEDIUM).parse(str);
  }
}

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This compliant solution makes DateHandler thread-safe by synchronizing statements within the parse() method [API 2011]:

final class DateHandler {
  private static DateFormat format =
    DateFormat.getDateInstance(DateFormat.MEDIUM);

  public static java.util.Date parse(String str) throws ParseException {
    synchronized (format) {
      return format.parse(str);
    }
  }
}

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Technically, strict immutability of the referent is a stronger condition than is fundamentally required for safe publication. When it can be determined that a referent is thread-safe by design, the field that holds its reference may be declared volatile. However, this approach to using volatile decreases maintainability and should be avoided.

Bibliography

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