Here you can see that there are 2 public static void main (String args[]) in a single file with the name Test.java (specifically didn't use the name of file as either of the 2 classes names) and the 2 classes are with the default access specifier.
class Sum {
int add(int a, int b) {
return (a+b);
}
public static void main (String args[]) {
System.out.println(" using Sum class");
Sum a = new Sum();
System.out.println("Sum is :" + a.add(5, 10));
}
public static void main (int i) {
System.out.println(" Using Sum class main function with integer argument");
Sum a = new Sum();
System.out.println("Sum is :" + a.add(20, 10));
}
}
class DefClass {
public static void main (String args[]) {
System.out.println(" using DefClass");
Sum a = new Sum();
System.out.println("Sum is :" + a.add(5, 10));
Sum.main(null);
Sum.main(1);
}
}
When we compile the code Test.java it will generate 2 .class files (viz Sum.class and DefClass.class) and if we run Test.java we cannot run it as it won't find any main class with the name Test. Instead if we do java Sum or java DefClass both will give different outputs using different main(). To use the main method of Sum class we can use the class name Sum.main(null) or Sum.main(1)//Passing integer value in the DefClass main().
In a class scope we can have only one public static void main (String args[]) per class since a static method of a class belongs to a class and not to its objects and is called using its class name. Even if we create multiple objects and call the same static methods using them then the instance of the static method to which these call will refer will be the same.
We can also do the overloading of the main method by passing different set of arguments in the main. The Similar example is provided in the above code but by default the control flow will start with the public static void main (String args[]) of the class file which we have invoked using java classname. To invoke the main method with other set of arguments we have to explicitly call it from other classes.