What Restrictions Are Placed on Method Overriding

In Java, there are certain restrictions and rules placed on method overriding. Here are the key points:

1. Access Modifier: The access level of the overriding method must be the same or more accessible than the overridden method. For example, if a method in the superclass is declared as protected, the overriding method in the subclass cannot be private, but it can be protected or public.
   java

   // Example
class Superclass {
protected void exampleMethod() {
// code
}
}class Subclass extends Superclass {
   // This is valid
   protected void exampleMethod() {
   // code
   }
   }

2. Return Type: The return type of the overriding method must be the same as, or a subtype of, the return type of the overridden method. Covariant return types (returning a subtype) were introduced in Java 5.
   java

   // Example
class Superclass {
Number exampleMethod() {
// code
return 0;
}
}class Subclass extends Superclass {
   // Valid: Covariant return type
   Integer exampleMethod() {
   // code
   return 0;
   }
   }

3. Exception Handling: If the overridden method throws any checked exceptions, the overriding method can only throw the same, subclass of those exceptions, or no exception (unchecked exception).
   java

   // Example
class Superclass {
void exampleMethod() throws IOException {
// code
}
}class Subclass extends Superclass {
   // Valid: Same exception
   void exampleMethod() throws IOException {
   // code
   }

   // Valid: Subclass exception
   void exampleMethod() throws FileNotFoundException {
   // code
   }

   // Valid: No exception
   void exampleMethod() {
   // code
   }
   }

4. Static and Final Methods: It’s not possible to override a static method in Java. If a method in the superclass is declared as final, it cannot be overridden in any subclass.

These rules ensure that the behavior of polymorphism is maintained and that the overriding method in the subclass is a true subtype of the overridden method in the superclass.