Overriding, Overloading methods (Interview Questions)/February 25, 2024

1. What must be true for the access modifier of a subclass when it is overriding a method in the superclass?
   
   Answer:
   The overriding method cannot have a more restrictive access modifier than the method being overridden.
   You are allowed to override a method as long as the overiding method's access modifier is not more restrictive than the original one. This means you can do the following:
   Allowed:
   

   class Parent {
     public void aMethod() {
     }
   }
   class Child extends Parent {
     public void aMethod() {
     }
   }
   

   
   You are not allowed to do the following:
   Not Allowed:

   class Parent {
     public void aMethod() {
     }
   }
   class Child extends Parent {
     protected void aMethod() {
     }
   }
   

   In the above example, protected in the subclass is more restrictive than public in the superclass.

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2. What must be observed when overriding methods that throw exceptions?
   
   Answer:
   The overriding method must not throw checked exceptions that are new or broader than those declared by the overridden method.

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3. How does the JVM determine which method to run when a method is overridden?
   
   Answer:
   At runtime the JVM uses virtual method invocation to dynamically select the actual version of the method that will run, based on the actual instance.

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4. What is the relation between a superclass and subclass reference?
   
   Answer:
   A superclass reference can always refer to a subclass instance.

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5. What is the difference between method overriding and method overloading in Java?
   
   Answer:
   The overriding method must fulfill the contract of the superclass. Overloading occurs in Java when you have a different argument list.

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6. What will happen if the method of the subclass does not have the same arugment list as the method of the superclass?
   
   Answer:
   If the method of the subclass does not have the same argument list as the method of the superclass, you will overload instead of override the method.

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7. If a method in a subclass throws an exception, what must be true for the method in the superclass?
   
   Answer:
   General Rule: If the method in the subclass throws an exception, then the method in the superclass must also throw that exception.
   Example: If a method throws FileNotFoundException in a subclass, the overridden method in the superclass must throw the same exception.

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8. What is true about the overriding method of a subclass in relation to the method being overridden in the superclass?
   
   Answer:
   The overriding method must NOT throw checked exceptions that are broader (more encompassing) than those declared by the overridden method (in the superclass).

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9. What types of exceptions can the overriding method in the subclass throw?
   Answer:
   The overriding method can throw narrower or fewer exceptions.

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10. What is the relationship between a superclass and a subclass when it comes to throwing exceptions in Java?
    
    Answer:
    A method in the superclass may throw an exception. However, the overriding method in the subclass does not have to throw that same exception.