On Thu, 7 Sep 2023 12:24:58 GMT, Rémi Forax <fo...@openjdk.org> wrote:
>> This PR proposes to slightly improve some iterators of `AbstractMap`: >> >> * Code reuse >> * A field declared `final` >> * Add missing `@Override` annotations > > Hello, > In Java, sharing code may have a runtime cost (or not) depending on the shape > of the code, because the VM may have to speculate on the class of some value > at runtime. > Here, in hasNext() and remove(), the VM has to find the class of the field > 'i' at runtime. > > Iterators are performance sentive (they are used in for loop) and for that > they need the escape analysis to work. > If the iterator code is polymorphic, so part of the code may be unknown so > the escape analysis will consider that the iterator escape. So usually, it's > a good practice to not share the iterator code. > > Also the field should be package private (or even maybe private) but not > protected. Protected is very rare in Java because usually classes that share > implementation details are in the same package (or in the same nestmate nest). @forax Note that HashMap uses a similar subclassing idiom for the iterators of the keySet, values, and entrySet collections in order to share the iterator logic: https://github.com/openjdk/jdk/blob/jdk-21%2B35/src/java.base/share/classes/java/util/HashMap.java#L1626 ------------- PR Comment: https://git.openjdk.org/jdk/pull/15615#issuecomment-1710574566
