It's somewhat logical, though, that T[0] is faster than T[size]. In both cases, the given array is checked to see if it's large enough to fit the collection contents. If it isn't, then a new array is allocated. By deferring the new array allocation operation to the toArray() method call, you avoid two array length checks.
TL;DR: this is probably a spurious micro-optimization. On Fri, 27 Dec 2019 at 08:48, Gary Gregory <garydgreg...@gmail.com> wrote: > > I wonder where this should be documented. We could add a // comment to each > call site, that seems the simplest. Adding a package or component level > documentation in the style guideline for example could easily be overlooked > by someone in a debugger for example. So each call site would be best IMO > something like > // Using an empty array can be faster > I don't really want a link to an external random blog in the source. > > Thoughts? > > Then we can consider doing it throughout Commons. > > Gary > > On Fri, Dec 27, 2019 at 7:23 AM Pascal Schumacher <pascalschumac...@gmx.net> > wrote: > > > Feel free to revert the changes. > > > > I would revert my changes, but Garry did some follow-up changes so these > > would to be reverted first. > > > > Am 27.12.2019 um 12:33 schrieb sebb: > > > As that article says in conclusion, T[0] seems currently faster, but that > > > may not always be the case with future VMs. > > > > > > Also it says that IntelliJ IDEA and PMD recommend using T[size] rather > > than > > > T[0]. > > > If we release code with T[0], I suspect we will get complaints that the > > > code is not efficient according to x, y and z. > > > > > > I'm not convinced that the change is worth it, but if it is agreed the > > code > > > must be thoroughly documented to try and forestall complaints. > > > According to the article, using a constant empty array is faster, but > > only > > > marginally. If there is a constant available it would probably make sense > > > to use it. > > > This should also be documented, as it affects the return value for the > > > empty case. > > > > > > S. > > > On Fri, 27 Dec 2019 at 09:28, Pascal Schumacher < > > pascalschumac...@gmx.net> > > > wrote: > > > > > >> see https://shipilev.net/blog/2016/arrays-wisdom-ancients/ > > >> > > >> Am 27.12.2019 um 01:24 schrieb sebb: > > >>> Also, where is it documented that modern JVMs are faster? > > >>> To which JVMs does this apply? > > >>> > > >>> S. > > >>> > > >>> On Thu, 26 Dec 2019 at 22:08, Gary Gregory <garydgreg...@gmail.com> > > >> wrote: > > >>>> Please do not cause garbage to apparently be generated all over the > > >> place > > >>>> by creating new empty arrays all the time. Use the constants Commons > > >> Lang > > >>>> constants already defines; see ArrayUtils. > > >>>> > > >>>> Gary > > >>>> > > >>>> On Thu, Dec 26, 2019 at 4:48 PM <pascalschumac...@apache.org> wrote: > > >>>> > > >>>>> This is an automated email from the ASF dual-hosted git repository. > > >>>>> > > >>>>> pascalschumacher pushed a commit to branch master > > >>>>> in repository https://gitbox.apache.org/repos/asf/commons-lang.git > > >>>>> > > >>>>> > > >>>>> The following commit(s) were added to refs/heads/master by this push: > > >>>>> new 84668a2 Use Collection#toArray(new T[0]) instead of a > > >> presized > > >>>>> array as it is faster on modern JVMs. > > >>>>> 84668a2 is described below > > >>>>> > > >>>>> commit 84668a2d980316a580030fd64764cb072b520b09 > > >>>>> Author: pascalschumacher <pascalschumac...@gmx.net> > > >>>>> AuthorDate: Thu Dec 26 22:48:12 2019 +0100 > > >>>>> > > >>>>> Use Collection#toArray(new T[0]) instead of a presized array as > > >> it is > > >>>>> faster on modern JVMs. > > >>>>> --- > > >>>>> src/main/java/org/apache/commons/lang3/CharSet.java | > > 2 > > >> +- > > >>>>> src/main/java/org/apache/commons/lang3/StringUtils.java | > > 10 > > >>>>> +++++----- > > >>>>> .../org/apache/commons/lang3/exception/ExceptionUtils.java | > > 6 > > >>>> +++--- > > >>>>> src/main/java/org/apache/commons/lang3/reflect/FieldUtils.java | > > 4 > > >> ++-- > > >>>>> .../java/org/apache/commons/lang3/reflect/MethodUtils.java | > > 2 > > >> +- > > >>>>> src/main/java/org/apache/commons/lang3/reflect/TypeUtils.java | > > 2 > > >> +- > > >>>>> src/main/java/org/apache/commons/lang3/text/StrTokenizer.java | > > 4 > > >> ++-- > > >>>>> .../org/apache/commons/lang3/time/DurationFormatUtils.java | > > 2 > > >> +- > > >>>>> .../java/org/apache/commons/lang3/time/FastDatePrinter.java | > > 2 > > >> +- > > >>>>> .../commons/lang3/concurrent/EventCountCircuitBreakerTest.java | > > 2 > > >> +- > > >>>>> 10 files changed, 18 insertions(+), 18 deletions(-) > > >>>>> > > >>>>> diff --git a/src/main/java/org/apache/commons/lang3/CharSet.java > > >>>>> b/src/main/java/org/apache/commons/lang3/CharSet.java > > >>>>> index 3fdfd07..7955115 100644 > > >>>>> --- a/src/main/java/org/apache/commons/lang3/CharSet.java > > >>>>> +++ b/src/main/java/org/apache/commons/lang3/CharSet.java > > >>>>> @@ -225,7 +225,7 @@ public class CharSet implements Serializable { > > >>>>> // NOTE: This is no longer public as CharRange is no longer a > > public > > >>>>> class. > > >>>>> // It may be replaced when CharSet moves to Range. > > >>>>> /*public*/ CharRange[] getCharRanges() { > > >>>>> - return set.toArray(new CharRange[set.size()]); > > >>>>> + return set.toArray(new CharRange[0]); > > >>>>> } > > >>>>> > > >>>>> > > >>>>> > > >> > > //----------------------------------------------------------------------- > > >>>>> diff --git a/src/main/java/org/apache/commons/lang3/StringUtils.java > > >>>>> b/src/main/java/org/apache/commons/lang3/StringUtils.java > > >>>>> index abde7ec..d629806 100644 > > >>>>> --- a/src/main/java/org/apache/commons/lang3/StringUtils.java > > >>>>> +++ b/src/main/java/org/apache/commons/lang3/StringUtils.java > > >>>>> @@ -7507,7 +7507,7 @@ public class StringUtils { > > >>>>> currentType = type; > > >>>>> } > > >>>>> list.add(new String(c, tokenStart, c.length - > > tokenStart)); > > >>>>> - return list.toArray(new String[list.size()]); > > >>>>> + return list.toArray(new String[0]); > > >>>>> } > > >>>>> > > >>>>> /** > > >>>>> @@ -7735,7 +7735,7 @@ public class StringUtils { > > >>>>> } > > >>>>> } > > >>>>> > > >>>>> - return substrings.toArray(new String[substrings.size()]); > > >>>>> + return substrings.toArray(new String[0]); > > >>>>> } > > >>>>> > > >>>>> // > > >>>>> > > ----------------------------------------------------------------------- > > >>>>> @@ -7923,7 +7923,7 @@ public class StringUtils { > > >>>>> if (match || preserveAllTokens && lastMatch) { > > >>>>> list.add(str.substring(start, i)); > > >>>>> } > > >>>>> - return list.toArray(new String[list.size()]); > > >>>>> + return list.toArray(new String[0]); > > >>>>> } > > >>>>> > > >>>>> /** > > >>>>> @@ -8022,7 +8022,7 @@ public class StringUtils { > > >>>>> if (match || preserveAllTokens && lastMatch) { > > >>>>> list.add(str.substring(start, i)); > > >>>>> } > > >>>>> - return list.toArray(new String[list.size()]); > > >>>>> + return list.toArray(new String[0]); > > >>>>> } > > >>>>> > > >>>>> /** > > >>>>> @@ -8835,7 +8835,7 @@ public class StringUtils { > > >>>>> if (list.isEmpty()) { > > >>>>> return null; > > >>>>> } > > >>>>> - return list.toArray(new String[list.size()]); > > >>>>> + return list.toArray(new String[0]); > > >>>>> } > > >>>>> > > >>>>> /** > > >>>>> diff --git > > >>>>> > > a/src/main/java/org/apache/commons/lang3/exception/ExceptionUtils.java > > >>>>> > > b/src/main/java/org/apache/commons/lang3/exception/ExceptionUtils.java > > >>>>> index 5969614..dd154e3 100644 > > >>>>> --- > > >>>> a/src/main/java/org/apache/commons/lang3/exception/ExceptionUtils.java > > >>>>> +++ > > >>>> b/src/main/java/org/apache/commons/lang3/exception/ExceptionUtils.java > > >>>>> @@ -274,7 +274,7 @@ public class ExceptionUtils { > > >>>>> } > > >>>>> frames.addAll(trace); > > >>>>> } > > >>>>> - return frames.toArray(new String[frames.size()]); > > >>>>> + return frames.toArray(new String[0]); > > >>>>> } > > >>>>> > > >>>>> /** > > >>>>> @@ -325,7 +325,7 @@ public class ExceptionUtils { > > >>>>> while (frames.hasMoreTokens()) { > > >>>>> list.add(frames.nextToken()); > > >>>>> } > > >>>>> - return list.toArray(new String[list.size()]); > > >>>>> + return list.toArray(new String[0]); > > >>>>> } > > >>>>> > > >>>>> /** > > >>>>> @@ -438,7 +438,7 @@ public class ExceptionUtils { > > >>>>> */ > > >>>>> public static Throwable[] getThrowables(final Throwable > > >> throwable) { > > >>>>> final List<Throwable> list = getThrowableList(throwable); > > >>>>> - return list.toArray(new Throwable[list.size()]); > > >>>>> + return list.toArray(new Throwable[0]); > > >>>>> } > > >>>>> > > >>>>> /** > > >>>>> diff --git > > >>>>> a/src/main/java/org/apache/commons/lang3/reflect/FieldUtils.java > > >>>>> b/src/main/java/org/apache/commons/lang3/reflect/FieldUtils.java > > >>>>> index d72dc53..553be4e 100644 > > >>>>> --- a/src/main/java/org/apache/commons/lang3/reflect/FieldUtils.java > > >>>>> +++ b/src/main/java/org/apache/commons/lang3/reflect/FieldUtils.java > > >>>>> @@ -199,7 +199,7 @@ public class FieldUtils { > > >>>>> */ > > >>>>> public static Field[] getAllFields(final Class<?> cls) { > > >>>>> final List<Field> allFieldsList = getAllFieldsList(cls); > > >>>>> - return allFieldsList.toArray(new > > Field[allFieldsList.size()]); > > >>>>> + return allFieldsList.toArray(new Field[0]); > > >>>>> } > > >>>>> > > >>>>> /** > > >>>>> @@ -237,7 +237,7 @@ public class FieldUtils { > > >>>>> */ > > >>>>> public static Field[] getFieldsWithAnnotation(final Class<?> > > cls, > > >>>>> final Class<? extends Annotation> annotationCls) { > > >>>>> final List<Field> annotatedFieldsList = > > >>>>> getFieldsListWithAnnotation(cls, annotationCls); > > >>>>> - return annotatedFieldsList.toArray(new > > >>>>> Field[annotatedFieldsList.size()]); > > >>>>> + return annotatedFieldsList.toArray(new Field[0]); > > >>>>> } > > >>>>> > > >>>>> /** > > >>>>> diff --git > > >>>>> a/src/main/java/org/apache/commons/lang3/reflect/MethodUtils.java > > >>>>> b/src/main/java/org/apache/commons/lang3/reflect/MethodUtils.java > > >>>>> index bbd5019..491470d 100644 > > >>>>> --- a/src/main/java/org/apache/commons/lang3/reflect/MethodUtils.java > > >>>>> +++ b/src/main/java/org/apache/commons/lang3/reflect/MethodUtils.java > > >>>>> @@ -878,7 +878,7 @@ public class MethodUtils { > > >>>>> final boolean > > >>>>> searchSupers, final boolean ignoreAccess) { > > >>>>> final List<Method> annotatedMethodsList = > > >>>>> getMethodsListWithAnnotation(cls, annotationCls, searchSupers, > > >>>>> ignoreAccess); > > >>>>> - return annotatedMethodsList.toArray(new > > >>>>> Method[annotatedMethodsList.size()]); > > >>>>> + return annotatedMethodsList.toArray(new Method[0]); > > >>>>> } > > >>>>> > > >>>>> /** > > >>>>> diff --git > > >>>> a/src/main/java/org/apache/commons/lang3/reflect/TypeUtils.java > > >>>>> b/src/main/java/org/apache/commons/lang3/reflect/TypeUtils.java > > >>>>> index 2a6ccd0..f9df8c6 100644 > > >>>>> --- a/src/main/java/org/apache/commons/lang3/reflect/TypeUtils.java > > >>>>> +++ b/src/main/java/org/apache/commons/lang3/reflect/TypeUtils.java > > >>>>> @@ -1149,7 +1149,7 @@ public class TypeUtils { > > >>>>> } > > >>>>> } > > >>>>> > > >>>>> - return types.toArray(new Type[types.size()]); > > >>>>> + return types.toArray(new Type[0]); > > >>>>> } > > >>>>> > > >>>>> /** > > >>>>> diff --git > > >>>> a/src/main/java/org/apache/commons/lang3/text/StrTokenizer.java > > >>>>> b/src/main/java/org/apache/commons/lang3/text/StrTokenizer.java > > >>>>> index c9ab666..97fae7d 100644 > > >>>>> --- a/src/main/java/org/apache/commons/lang3/text/StrTokenizer.java > > >>>>> +++ b/src/main/java/org/apache/commons/lang3/text/StrTokenizer.java > > >>>>> @@ -604,10 +604,10 @@ public class StrTokenizer implements > > >>>>> ListIterator<String>, Cloneable { > > >>>>> if (chars == null) { > > >>>>> // still call tokenize as subclass may do some > > work > > >>>>> final List<String> split = tokenize(null, 0, 0); > > >>>>> - tokens = split.toArray(new String[split.size()]); > > >>>>> + tokens = split.toArray(new String[0]); > > >>>>> } else { > > >>>>> final List<String> split = tokenize(chars, 0, > > >>>>> chars.length); > > >>>>> - tokens = split.toArray(new String[split.size()]); > > >>>>> + tokens = split.toArray(new String[0]); > > >>>>> } > > >>>>> } > > >>>>> } > > >>>>> diff --git > > >>>>> > > a/src/main/java/org/apache/commons/lang3/time/DurationFormatUtils.java > > >>>>> > > b/src/main/java/org/apache/commons/lang3/time/DurationFormatUtils.java > > >>>>> index 83af2e0..4a75237 100644 > > >>>>> --- > > >>>> a/src/main/java/org/apache/commons/lang3/time/DurationFormatUtils.java > > >>>>> +++ > > >>>> b/src/main/java/org/apache/commons/lang3/time/DurationFormatUtils.java > > >>>>> @@ -564,7 +564,7 @@ public class DurationFormatUtils { > > >>>>> if (inLiteral) { // i.e. we have not found the end of the > > >>>> literal > > >>>>> throw new IllegalArgumentException("Unmatched quote in > > >>>>> format: " + format); > > >>>>> } > > >>>>> - return list.toArray(new Token[list.size()]); > > >>>>> + return list.toArray(new Token[0]); > > >>>>> } > > >>>>> > > >>>>> > > >>>>> > > >> > > //----------------------------------------------------------------------- > > >>>>> diff --git > > >>>>> a/src/main/java/org/apache/commons/lang3/time/FastDatePrinter.java > > >>>>> b/src/main/java/org/apache/commons/lang3/time/FastDatePrinter.java > > >>>>> index a5edb28..888d3fb 100644 > > >>>>> --- > > a/src/main/java/org/apache/commons/lang3/time/FastDatePrinter.java > > >>>>> +++ > > b/src/main/java/org/apache/commons/lang3/time/FastDatePrinter.java > > >>>>> @@ -160,7 +160,7 @@ public class FastDatePrinter implements > > >> DatePrinter, > > >>>>> Serializable { > > >>>>> */ > > >>>>> private void init() { > > >>>>> final List<Rule> rulesList = parsePattern(); > > >>>>> - mRules = rulesList.toArray(new Rule[rulesList.size()]); > > >>>>> + mRules = rulesList.toArray(new Rule[0]); > > >>>>> > > >>>>> int len = 0; > > >>>>> for (int i=mRules.length; --i >= 0; ) { > > >>>>> diff --git > > >>>>> > > >> > > a/src/test/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreakerTest.java > > >> > > b/src/test/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreakerTest.java > > >>>>> index b3fb5cf..2819006 100644 > > >>>>> --- > > >>>>> > > >> > > a/src/test/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreakerTest.java > > >>>>> +++ > > >>>>> > > >> > > b/src/test/java/org/apache/commons/lang3/concurrent/EventCountCircuitBreakerTest.java > > >>>>> @@ -407,7 +407,7 @@ public class EventCountCircuitBreakerTest { > > >>>>> */ > > >>>>> public void verify(final Boolean... values) { > > >>>>> assertArrayEquals(values, > > >>>>> - changedValues.toArray(new > > >>>>> Boolean[changedValues.size()])); > > >>>>> + changedValues.toArray(new Boolean[0])); > > >>>>> } > > >>>>> } > > >>>>> } > > >>>>> > > >>>>> > > >> > > >> --------------------------------------------------------------------- > > >> To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org > > >> For additional commands, e-mail: dev-h...@commons.apache.org > > >> > > >> > > > > > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org > > For additional commands, e-mail: dev-h...@commons.apache.org > > > > -- Matt Sicker <boa...@gmail.com> --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
