CODEWITHSUNDEEP
java
user3773562
user3773562

Reputation:

whats the difference between the class files generated for a class with main function and the one without main function?

I am a beginner in java i want to know whats the difference between the class files created for a class with main function and the one created for a class without main function.we can create a class without a main function and able to compile it so whats the difference between the class files being generated.It may look like a stupid question but i just want to know the answer for this.

Thank you in advance

Upvotes: 1

Views: 151

Answers (2)

Christian Kuetbach
Christian Kuetbach

Reputation: 16060

There is no difference in the compiler.

In the compiled bytecode are methods.

If there ist a 

public static void main(String[] args){}

You will get a Class, which can be started by calling

java ClassName

It is just a convention, that the main-method is started, if called by Java.

update

Prior to Java 7 you could start a JavaClass like this (without a main-method):

//Don't use this
public class RunnableNoMain{
   static { new RunnableNoMain(); } //creates an instance.
}

The static initializer will create an instance and execute code. Right after, there will be a NoSuchMethodException (main ist not found)

Upvotes: 2

morgano
morgano

Reputation: 17422

There is no special bytecode for one class with a public static void main(String ..args), that method is compiled the same way as any other method.

The difference is made by the Java Virtual Machine (not the compiler), whose specification states this:

The Java Virtual Machine starts up by creating an initial class, which is specified in an implementation-dependent manner, using the bootstrap class loader (§5.3.1). The Java Virtual Machine then links the initial class, initializes it, and invokes the public class method void main(String[]).

Upvotes: 4

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