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

Question

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.

There is no `static` method overriding, but there is **hiding**. In the first case, `ClassB` hides the `main` method from `ClassA`. In the second case `ClassB` does not hide the `main` method so the one from `ClassA` is called. — Boris the Spider, Apr 06 '15 at 13:12

Maroun · Accepted Answer · 2015-04-06T13:11:09.837

7

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.

edited Apr 06 '15 at 13:11

answered Apr 06 '15 at 13:10

Maroun

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we cannot override static methods as java says :) – Bhargav Modi Apr 06 '15 at 13:11
1

@BhargavModi Indeed, override is a bad word. Fixed. – Maroun Apr 06 '15 at 13:12
@Maroun Maroun, this is what I proved with my classes. @ Boris the Spider; please try to execute. – Saurabh Jhunjhunwala Apr 06 '15 at 13:18

score 2 · Answer 2 · answered Apr 06 '15 at 13:16

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.

score 0 · Answer 3 · answered Apr 06 '15 at 13:14

0

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

answered Apr 06 '15 at 13:14

Saif

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

3 Answers3