Thread: java program without main method

Hi every one i want to ask you a Question that :-----> Can we made a java program without main method be sure it should not be an applet?


Second Q. :--> I want to know all the method's of Array declaration in java??


Third Q. :----> I want to know does main method of java is always a primary thread for java can we change the sequence of main thread from another than please tell me???

Hey please send a detail's explanation of these Question if possible than send a small program with ans of these Question...

i too want the answer for these questions buddy,any body help plz..

class WithoutMain
{
static
{
System.out.println("This is a Program without a main method.");
System.exit(0);
}
}

The program wont run. Shows the following error.
Error: Could not find or load main class WithoutMain

Hi..

For the question 1:

Yes,We can write a Java program which does not have main method at all. This can be done using the static block of the class.

How this works is that static initialization blocks get executed as soon as the class is loaded, even before the main method is called. During run time, JVM will search for the main method after exiting from this block. If it does not find the main method, it throws an exception. To avoid the exception System.exit(0); statement is used which terminates the program at the end of the static block itself.

class WithoutMain
{
static
{
System.out.println("This java program ran without the main method");
System.exit(0);

}
}

For the question 2:
Some examples:

Exception ae[] = new Exception[3];
Object aao[][] = new Exception[2][3];
int[] factorial = { 1, 1, 2, 6, 24, 120, 720, 5040 };
char ac[] = { 'n', 'o', 't', ' ', 'a', ' ',
'S', 't', 'r', 'i', 'n', 'g' };
String[] aas = { "array", "of", "String", };

For question 3:
I think,we can change the sequence,but,i am not sure.

Thanks n' Regards
Neelima

Hi neelim ,
The program you provided will compile successfully,but will not execute due to main not found exception.

Thanks neelim It's the ideal solution for me....///

sorry for the answer given by neelim for the question number 1.

No java program executes without main method.

until unless u wil call that class WithoutMain in the main method , static block will not produce output

sorry for the answer given by neelim for the question number 1.
No java program executes without main method.
until unless u wil call that class WithoutMain in the main method , static block will not produce output

Neelim's answer for Question Number 1 is correct...
it will generate o/p.
Memory for the Satic members will be allocated during the compile time itself. and the Interpreter looking for the main method during the execution time if it is not avail , then it throws an java.lang.NoSuchMethodError.if we use System.exit(0) then the programs perfectly run...

Actually both Neelim & Umeshap are correct to an extent. The code provided by Neelim though correct will not execute by itself as it has no main. So what it needs is another class instantiating it (ie. loading it) as below:

public class NoMain
{
static
{
System.out.println("This is an executable class even without a main method");
System.exit(0);
}
}

public class NoMainTest
{
public static void main(String[] args)
{
new NoMain();
}
}

So yes we can have a java prg without the main method...

Hope this helps.

Neelam's answer is correct,recently i heard about this concept

yaa we can execute an java program without main method..




Thanks
Sagar Chugh

I ran this program. Wow amazing. It ran successfully. But I just want to know how it works internally?

can anybody tell wats the use of THIS keyword in java??????????

this code is very tough to understand riju i m beginer so can u give some simple code....for this keyword

Originally Posted by raghavmishra

can anybody tell wats the use of THIS keyword in java??????????

It returns the reference to the current object

Ur first answer:
Yes,u can make a java program without main().You can also compile it and a .class file will be generated after compilation.But you cannot execute it,because when you try to execute this .class file, you will get a runtime error called java.lang.NoSuchMethodError:main.

Ur second answer:
The various ways in which we can declare an array are:
First way:
Here,only an array is created but elements in the array get default values.
int [] arr=new int [5];
Second way:
int arr[]=new int[10];
Third way:
Here in addition to declaring the array,you are also giving the values to the elements in the array.Here,you dont need to specofy the size of array.Depending on the number of entries in the curly braces i.e{},the size is automatically assigned to the array.So,here the size of array becomes 4.
int arr[]={1,2,6,9};
Fourth way:
int arr[]=new int [] {1,2,3};

Ur third answer:
main() will always be the first thread to be executed.When the java run time executes the program,the first thread to be executed is main().From inside main(),other threads are created and then those threads are started.Each thread has got a priority.In java, priority of main() is 5.You can set the priority of other threads greater than the priority of main().So,if you set the other thread at a greater priority,that thread will be given more importance by the JVM.But,main() must be the first thread executed by the JVM and other threads can be started only from within main. Also main() is the last thread to be executed before the program ends.

There is no magic behind this. static block gets called when ClassLoader tries to load the class.after loading the class only jvm calls the main method. so no wonder it executes the statements in the static block with out main method.