Hi Daniel, thanks, this is what I was looking for!
And what about JavaDoc of Parameter.isNamePresent()? Should we keep it as is, I mean pointing out to 'MethodParameters' attribute of a class file? Regards, Sergey > Hi Sergey, > > I believe you need to compile with `-parameters` > > https://docs.oracle.com/en/java/javase/18/docs/specs/man/javac.html > > best regards, > > -- daniel > > On 29/06/2022 07:54, Сергей Цыпанов wrote: > >> This question was asked originally here: >> https://stackoverflow.com/questions/72787286/executable-hasrealparameterdata-and-parameter-isnamepresent-dont-work-as-ex >> but as soon as I got no answer I've decided to try it here adding some >> concerns regarding JavaDoc of Parameter.isNamePresent() >> >> With ad-hoc built JDK 19 (having exposed >> `Executable.hasRealParameterData()`) I take the code >> >> public class Main { >> >> public static void main(String[] args) throws NoSuchMethodException { >> Method foo = Main.class.getMethod("foo", String.class, int.class); >> System.out.println(foo.hasRealParameterData()); >> } >> >> public void foo(String parameter1, int parameter2) {} >> } >> >> and compile it with >> >> % javac Main.java >> >> Then I run compiled Java class and it prints `false` into console. This is >> fine because decompiled `Main` class looks like >> >> public class Main { >> //... >> public void foo(String var1, int var2) {} // parameter names are not 'real' >> } >> >> i.e. parameter names are synthetic. >> >> This behaviour is understandable. >> >> Then I take the same Java sources and recompile the class with >> >> javac -g:vars Main.java >> >> I run the same code again and again it prints `false` to console. This >> puzzles me, because now the compiled code looks different: >> >> public class Main { >> //... >> public void foo(String parameter1, int parameter2) {} // parameter names are >> 'real' >> } >> >> Same happens if for recompilation I use plain -g flag (generates all >> auxiliary data). >> >> Now let's stop calling JDK's private API and rely only on the methods >> available out-of-the-box, >> e.g. `Parameter.isNamePresent()` (this one calls >> `Executable.hasRealParameterData()` under the hood): >> >> public static void main(String[] args) throws NoSuchMethodException { >> Method foo = Main.class.getMethod("foo", String.class, int.class); >> Parameter parameter1 = foo.getParameters()[0]; >> Parameter parameter2 = foo.getParameters()[1]; >> System.out.println(parameter1.isNamePresent()); >> System.out.println(parameter2.isNamePresent()); >> } >> >> public void foo(String parameter1, int parameter2) {} >> >> And again, no matter how I compile the sources, this code prints `false >> false`. >> >> So my two questions are >> 1) whether this is a bug or am I doing something wrong? >> 2) is it possible somehow to change the behaviour to have at least >> Parameter.isNamePresent() returning true >> >> P.S. Parameter.isNamePresent() works unexpectedly even when I run it on >> conventional, not hacked JDK. >> >> P.P.S. In compiled code I see 'real' parameter names, but if I stop at debug >> point in IDEA parameter name is suddenly `arg0` in `Parameter.name` field. >> >> P.P.P.S. I think that JavaDoc of Parameter.isNamePresent() should be changed >> as soon as now it points out to 'MethodParameters' attribute of a class file >> which is confusing to me as to end user of Java because I cannot understand >> from plain Java code what are those 'MethodParameters' and what will >> be returned for any of my methods.
