I’m Looking for a definitive answer from a primary or secondary source for why (notably) Java and C# decided to have a static method as their entry point, rather than representing an application instance by an instance of an Application class (with the entry point being an appropriate constructor).
Background and details of my prior research
This has been asked before. Unfortunately, the existing answers are merely begging the question. In particular, the following answers don’t satisfy me, as I deem them incorrect:
- There would be ambiguity if the constructor were overloaded. – In fact, C# (as well as C and C++) allows different signatures for
Mainso the same potential ambiguity exists, and is dealt with. - A
staticmethod means no objects can be instantiated before so order of initialisation is clear. – This is just factually wrong, some objects are instantiated before (e.g. in a static constructor). - So they can be invoked by the runtime without having to instantiate a parent object. – This is no answer at all.
Just to justify further why I think this is a valid and interesting question:
-
Many frameworks do use classes to represent applications, and constructors as entry points. For instance, the VB.NET application framework uses a dedicated main dialog (and its constructor) as the entry point1.
-
Neither Java nor C# technically need a main method. Well, C# needs one to compile, but Java not even that. And in neither case is it needed for execution. So this doesn’t appear to be a technical restriction. And, as I mentioned in the first paragraph, for a mere convention it seems oddly unfitting with the general design principle of Java and C#.
To be clear, there isn’t a specific disadvantage to having a static main method, it’s just distinctly odd, which made me wonder if there was some technical rationale behind it.
I’m interested in a definitive answer from a primary or secondary source, not mere speculations.
1 Although there is a callback (Startup) which may intercept this.
Best Answer
TL;DR
In Java, the reason of
public static void main(String[] args)is thatFor C#, the reasoning is transitively similar so to speak. Language designers kept the program entry point syntax familiar for programmers coming from Java. As C# architect Anders Hejlsberg puts it,
Long version
expanding above and backed up with boring references.
java Terminator Hasta la vista Baby!
VM Spec, 2.17.1 Virtual Machine Start-up
...see also: Appendix: I need your clothes, your boots and your motorcycle
execution targeted for use like typical scripts in command line interface.
important sidestep
...that helps avoid a couple of false traces in our investigation.
VM Spec, 1.2 The Java Virtual Machine
I noticed above when studying prior chapter - 1.1 History which I thought could be helpful (but turned out useless).
execution is governed by VM spec alone, which
explicitly declares that it has nothing to do with Java language
=> OK to ignore JLS and anything Java language related at all
Gosling: a compromise between C and scripting language...
Based on above, I began searching the web for JVM history. Didn't help, too much garbage in results.
Then, I recalled legends about Gosling and narrowed down my search to Gosling JVM history.
Eureka! How The JVM Spec Came To Be
explicit declaration that at the moment of creation,
C and scripting have been considered most important influences.
Already seen nod to scripting in VM Spec 2.17.1,
command line arguments sufficiently explain
String[] argsbut
staticandmainaren't there yet, need to dig further...Note while typing this - connecting C, scripting and VM Spec 1.2 with its nothing-of-Java - I feel like something familiar, something... object oriented is slowly passing away. Take my hand and keep movin' Don't slow down we're nearly there now
Keynote slides are available online: 20_Gosling_keynote.pdf, quite convenient for copying key points.
page 3 The Prehistory of Java * What shaped my thinking page 9 NeWS * Networked Extensible Window System * A window system based on scripting.... PostScript (!!) page 16 A Big (but quiet) Goal: How close could I get to a "scripting" feel... page 19 The original concept * Was all about building networks of things, orchestrated by a scripting language * (Unix shells, AppleScript, ...) page 20 A Wolf in Sheeps Clothing * C syntax to make developers comfortableA-ha! Let's look closer at C syntax.
Are we getting closer? you bet. It is also worth following "main" link from above quote:
To be comfortable for C developer, program entry point has to be
main.Also, since Java requires any method to be in class,
Class.mainisas close as it gets: static invocation, just class name and dot,
no constructors please - C knows nothing like that.
This also transitively applies to C#, taking into account
the idea of easy migration to it from Java.
Readers thinking that familiar program entry point doesn't matter are kindly invited to search and check Stack Overflow questions where guys coming from Java SE are trying to write Hello World for Java ME MIDP. Note MIDP entry point has no
mainnorstatic.Conclusion
Based on above I would say that
static,mainandString[] argswere at the moments of Java and C# creation most reasonable choices to define program entry point.Appendix: I need your clothes, your boots and your motorcycle
Have to admit, reading VM Spec 2.17.1 was enormous fun.
Symbolic references from
Terminatoroh yeah.