Does all java programs start with main?

Question

Web servers like : Apache Tomcat.
App servers like : Weblogic.
EJB containers.
Android java container. 5> all the other java implementations?

All Java programs must start with a main method. Sometimes the method is visible to the programmer, and sometimes (such as with applets), it's not. — Hovercraft Full Of Eels, Feb 14 '13 at 03:07
It depends what you mean by "Java programs". Applets for example starts with `init`. — Pshemo, Feb 14 '13 at 03:14
@Pshemo: but that ignores the fact that there is a main method required somewhere, in this situation in the applet launching code, away from programmer's eyes, but regardless, the main *must* be there. — Hovercraft Full Of Eels, Feb 14 '13 at 03:15
@HovercraftFullOfEels your right. To start JVM we ned to use some variant of `java SomeClass` command which searches for `main` method in that class. — Pshemo, Feb 14 '13 at 03:19

score 1 · Answer 1 · edited May 23 '17 at 11:51

Usually yes. But no, it is not required ... as eloquently pointed out by this answer ... https://stackoverflow.com/a/2897323/1481262

Also, while instrumenting the code of applications (using the java.lang.instrument package), the execution starts with the premain method before the main is executed. - [1] [2].

[1] http://docs.oracle.com/javase/6/docs/api/java/lang/instrument/package-summary.html
[2] http://dhruba.name/2010/02/07/creation-dynamic-loading-and-instrumentation-with-javaagents/

score 0 · Answer 2 · answered Feb 14 '13 at 03:08

0

Yes. When you start a java program, you specify the class to use, and it's static main method is invoked with the command line arguments.

answered Feb 14 '13 at 03:08

Will Hartung

115,893
19
128
203

What about class is implementing threads then main functions is not needed. Everything goes in run method – big Feb 14 '13 at 03:14
@ShivamTiwari: but what code gets *started* in the JVM? There must be a main to get things started. – Hovercraft Full Of Eels Feb 14 '13 at 03:14

score 0 · Answer 3 · answered Feb 14 '13 at 03:09

0

Yes all java programs begin with main, though it's not necessary for each class to have it's individual main function.

answered Feb 14 '13 at 03:09

Shobhit Sharma

1,599
13
14

score 0 · Answer 4 · answered Feb 14 '13 at 03:12

0

Yes, all programs should start with main , It is something like contract between JDK and JRE.

answered Feb 14 '13 at 03:12

Siva Kumar Reddy G

1,274
3
18
32

score 0 · Answer 5 · answered Feb 14 '13 at 03:17

0

The JRE always starts from a main() method. However, it is possible to start up a JRE and use it to run several independent programs. For example, a browser will often run all its applets in the same JRE.

answered Feb 14 '13 at 03:17

Russell Zahniser

16,188
39
30

score 0 · Answer 6 · answered Feb 14 '13 at 03:56

Theoretically, you can write a custom launcher instead of java.exe, like here http://www.codeproject.com/Articles/17352/JVM-Launcher. Take a look at how they invoke main:

//Find the class
jclass    jcJclass = psJNIEnv->FindClass(mainClassName);

//Find the main method id
jmethodID jmMainMethod = 
    psJNIEnv-> GetStaticMethodID(jcJclass, "main", "([Ljava/lang/String;)V");

//Call the main method.
psJNIEnv->CallStaticVoidMethod(jcJclass, jmMainMethod, joApplicationArgs);

that is, it could be any method

Does all java programs start with main?

6 Answers6