Executable.hasRealParameterData() and Parameter.isNamePresent() don't work as expected
Сергей Цыпанов
sergei.tsypanov at yandex.ru
Wed Jun 29 06:54:43 UTC 2022
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.
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