Why is the main method static?

[server_crash]

I've often pondered over this subject. I know the main method has a special signature the JVM looks for, but why is it static?

[OurNation]

Dunno probly cus thats how they want it to work.

[Ghost]

i think static has to do w/ how its accessed

[server_crash]

i think static has to do w/ how its accessed

I already knew that.

[Narue]

>why is it static?
Primarily so that the JVM doesn't have to instantiate your controlling class to get an entry point into the program.

[server_crash]

>why is it static? Primarily so that the JVM doesn't have to instantiate your controlling class to get an entry point into the program.

So that would take longer than having a main method that does the same thing?

[Narue]

>So that would take longer than having a main method that does the same thing?
If main isn't static then an object of the class must be created first (unless the JVM wants to break its own rules, which isn't unheard of). By requiring main to be static, the environment avoids an unnecessary step. So yes, it would take slightly longer.

[server_crash]

>So that would take longer than having a main method that does the same thing? If main isn't static then an object of the class must be created first (unless the JVM wants to break its own rules, which isn't unheard of). By requiring main to be static, the environment avoids an unnecessary step. So yes, it would take slightly longer.

Thank you Narue, I believe I understand now.

[jwenting]

And be potentially impossible.
Which constructor should the JVM take after all?

[server_crash]

Which constructor should the JVM take after all?

The one it likes most?

[LunLun]

I'm not much of a C++ person, but I believe a different angle answer to your question might be found in the file java.c.

I downloaded the J2SE sources from the Sun's site:
http://www.sun.com/software/communitysource/j2se/java2/download.xml

I decompressed the archive and I took a look at the java.c file, from:
jdk-1_5_0-src-jrl\j2se\src\share\bin

I also found a possible answer to the unasked question
"Must the "main" method be public?"

{ /* Make sure the main method is public */
jint mods;
jmethodID mid;
jobject obj = (*env)->ToReflectedMethod(env, mainClass,
mainID, JNI_TRUE);

if( obj == NULL) { /* exception occurred */
ReportExceptionDescription(env);
goto leave;
}

mid =
(*env)->GetMethodID(env,
(*env)->GetObjectClass(env, obj),
"getModifiers", "()I");
if ((*env)->ExceptionOccurred(env)) {
ReportExceptionDescription(env);
goto leave;
}

mods = (*env)->CallIntMethod(env, obj, mid);
if ((mods & 1) == 0) { /* if (!Modifier.isPublic(mods)) ... */
message = "Main method not public.";
messageDest = JNI_TRUE;
goto leave;
}
}

[Narue]

>I also found a possible answer to the unasked question
There's no need to ask it when the asked question was "Why must main be static?". The language specification says that main has to be static, but doesn't explain why in any detail.

>And be potentially impossible.
Theoretically, the JVM could break its own rules (and the rules of OOD) and simply look for a main method as the entry point. But that's more effort than it's worth from my experience implementing object oriented language compilers. ;)

[server_crash]

What exactly is that rule your talking about?

If you guys find any readings on this, please post URL's.

[Narue]

java.sun.com is your friend. :)

[server_crash]

java.sun.com is your friend. :)

I never knew I had any friends?

[OurNation]

Me either I thought you just sat at your computer all day. JK

[server_crash]

Me either I thought you just sat at your computer all day. JK

I do? There's no joking in that.

[jwenting]

Java Language specification (second edition) section 12.1.4:
12.1.4 Invoke Test.main
Finally, after completion of the initialization for class Test (during which other consequential loading, linking, and initializing may have occurred), the method main of Test is invoked.
The method main must be declared public, static, and void. It must accept a single argument that is an array of strings. http://java.sun.com/docs/books/jls/ a mandatory link for everyone using Java, it's the final word on everything.

[server_crash]

Thank you, I like the link :cheesy:

[jwenting]

Told you the JLS is your friend :p

If you want more obscurity, here's the virtual machine specifications: http://java.sun.com/docs/books/vmspec/