12

Every Java program requires the presence of at least one class.

Is the above statement always true ?

Ani Menon
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Tony
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7 Answers7

25

Yes, you need at least one class to have a program, but no, you do not need any methods (contrary to some other answers).

The reason you need a class is because in Java, all code is inside classes. So to have any code, you need a class. However, code doesn't necessarily need to be in a method. It can also be in initializers. So, here is a complete Java program with no methods:

class LookMaNoMethods {
    static {
        System.out.println("Hello, world!");
        System.exit(0);
    }
}

And that gives...

$ javac LookMaNoMethods.java 
$ java LookMaNoMethods 
Hello, world!
$

EDIT : From Java 7 the above code with just static block and no main method does not produce any output. Main method is now compulsory. The code with no main method compiles successfully though.

Lord Nick
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rlibby
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    Interesting. A class with a static initializer is a valid program, even though there is no `main` method, which is then again required if there is no static initializer. I wonder what the standard says exactly about the requirement for an entry point. – Matti Virkkunen Mar 05 '11 at 14:53
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    The static-block is implemented as special kind of method internally (""). At least AFAIK. But still a good answer, I never was aware that you could start a method without a main(), too... Nice to know. – Boris Mar 05 '11 at 15:05
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    This program works only because the static initializer invokes `System.exit()` before the error message about a missing main method can be shown. – Paŭlo Ebermann Mar 05 '11 at 17:21
  • @Paŭlo Ebermann, yes, that's correct, but it is still orderly, not a race. The class is obviously loaded before any attempt to invoke `main`. – rlibby Mar 05 '11 at 21:43
9

From the JVM's point of view; yes. From a programmers view point, it can be a Class or an Enum.

public enum AAA {

    AAA;

    public static void main(final String[] args) {
        System.out.println("H");
    }

}

EDIT: Even if you have a class with empty main method, there are a lot of core classes which work behind the scene to just run the "empty" class of yours. A list of those classes (around 200 from the java.* package) can be viewed by setting the -verbose:class JVM parameter.

Sanjay T. Sharma
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    But an Enum is a class: http://download.oracle.com/javase/1.5.0/docs/api/java/lang/Enum.html. The new keyword is syntactic sugar that hides the class keyword. – duffymo Mar 05 '11 at 15:45
7

A program requires an entry point. An entry point has to be a method. In Java, every method must be contained in a class.

That would imply that every program must have a at least one class.

Matti Virkkunen
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    This is a very reasonable answer, but "an entry point has to be a method" is not *completely* true. See my answer for an entry point that is not a method. – rlibby Mar 05 '11 at 14:48
3

Yes. In Java you always need one class with the function main to have the JRE run it.

Konerak
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    This isn’t the reason. Ruby too is object oriented but it doesn’t need any class. The reason is just “because”. – Konrad Rudolph Mar 05 '11 at 14:29
  • Hmm I agree the implication is not true. How about 'sun wants it so?'/. – Konerak Mar 05 '11 at 14:30
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    Groovy (obviously built on top of JVM) does not require any classes to run. But the generated bytecode defines classes behind the scenes. – Tomasz Nurkiewicz Mar 05 '11 at 14:33
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    @Konrad - the statement wasn't that all object-oriented languages require a class, only Java. And other languages that have functions as first-class objects, unlike Java, might appear to allow functions as entry points, but they're still classes underneath. – duffymo Mar 05 '11 at 15:46
  • @duffymo Well, it was before @Konerak changed the answer. The current answer is correct. – Konrad Rudolph Mar 05 '11 at 22:00
1

yes , you need minimum one class.

Jacob Schoen
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stinepike
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0

No, classes aren't mandatory always we can write/define methods without using classes It is simple, Use INTERFACES , here is the code

public interface MainWithoutClass {
public static void main(String[] args) {
    System.out.println("Main method without Class");
}

public static void m1() {
    System.out.println("M1 method ");
    
}

}

Because Java 8 and after versions allows the interface to have a static methods .

Hrk Manbattulwar
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  • Although you are not really wrong with your statement, it is also not really correct: there is no class `java.lang.Interface` that corresponds to `java.lang.Class`– instead also your `MainWithoutClass` is represented by an instance of `Class`. So it is a `Class` although it is an interface. Have fun … – tquadrat Mar 21 '22 at 16:13
-2

JAVA required at least one class in a program because at the time of execution of Java programs we needed to provide the name of a class which contains the main () method.
so, it is compulsory to provide at least one class name to Java programs. ex--->`

class Test 
{ 
public static void main(String [] args)
{ 
System.out.println("Hello World");
}
}

so, javac _____ ("Here we have to give the name of java program in which we save")

java ______ ("Provide the name of a class which contain the main() method")

-----> according to our program

javac Hello (here I save the program name by Hello.java)

java Test (because Test class contains main() method)

Thank You

JATIN BEHUNE
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