CODEWITHSUNDEEP
javaprogram-entry-point
Bhargav Modi
Bhargav Modi

Reputation: 2655

why Exception or Error not generated when no main method found?

Ok just for sake knowledge , I tried below cases (Assume that Class A and B are in same package)

ClassA 

public class ClassA {

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

ClassB 

public class ClassB extends ClassA {

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

executing above ClassB it will produce output of B now after below change in classB

ClassB 

public class ClassB extends ClassA {
   //blank body
}

If I compile and run in terminal it gives me output A that was totally surprising as it should had given NoSuchMethodError as no main method was their so kindly explain the weird behavior ?

Note: Many answers contains Override word please use hiding as we cannot override static methods in java.

Upvotes: 9

Views: 417

Answers (3)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726539

In Java subclasses inherit all methods of their base classes, including their static methods.

Defining an instance method in the subclass with the matching name and parameters of a method in the superclass is an override. Doing the same thing for static methods hides the method of the superclass.

Hiding does not mean that the method disappears, though: both methods remain callable with the appropriate syntax. In your first example everything is clear: both A and B have their own main; calling A.main() prints A, while calling B.main() prints B.

In your second example, calling B.main() is also allowed. Since main is inherited from A, the result is printing A.

Upvotes: 2

Saif
Saif

Reputation: 7042

public static void main(String[] args) is just a method which you inherit from A in second case.

Upvotes: 0

Maroun
Maroun

Reputation: 95958

In the first case, you're hiding the main method since you're defining a new one in the subclass, in the second case you didn't you'll inherent A's main.

See The Java™ Tutorials - Overriding and Hiding:

If a subclass defines a static method with the same signature as a static method in the superclass, then the method in the subclass hides the one in the superclass.

Upvotes: 7

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