Improve antlr generated code [shared-ldap]
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Key: DIRSHARED-62
URL: https://issues.apache.org/jira/browse/DIRSHARED-62
Project: Directory Shared
Issue Type: Improvement
Environment: All
Reporter: Felix Knecht
The generated code by antlr could be improved regarding performance. Listed
classes below use the construct new Integer(...) a lot of times in their
constructor. If these classes are created many times it's an improvement to
have Integer.valueOf(...). Looking at the generated classes almost all values
for new Integer are in a range of [-128,128] what matches the criterias for
more performance [1].
Classes:
/shared-ldap/target/generated-sources/antlr/org/apache/directory/shared/ldap/aci/AntlrACIItemCheckerLexer.java
/shared-ldap/target/generated-sources/antlr/org/apache/directory/shared/ldap/aci/AntlrACIItemLexer.java
/shared-ldap/target/generated-sources/antlr/org/apache/directory/shared/ldap/subtree/AntlrSubtreeSpecificationCheckerLexer.java
/shared-ldap/target/generated-sources/antlr/org/apache/directory/shared/ldap/subtree/AntlrSubtreeSpecificationLexer.java
/shared-ldap/target/generated-sources/antlr/org/apache/directory/shared/ldap/trigger/AntlrTriggerSpecificationLexer.java
[1] http://findbugs.sourceforge.net/bugDescriptions.html#DM_NUMBER_CTOR
Using new Integer(int) is guaranteed to always result in a new object whereas
Integer.valueOf(int) allows caching of values to be done by the compiler, class
library, or JVM. Using of cached values avoids object allocation and the code
will be faster.
Values between -128 and 127 are guaranteed to have corresponding cached
instances and using valueOf is approximately 3.5 times faster than using
constructor. For values outside the constant range the performance of both
styles is the same.
Unless the class must be compatible with JVMs predating Java 1.5, use either
autoboxing or the valueOf() method when creating instances of Long, Integer,
Short, Character, and Byte.
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