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Lesson 9Overloading and overriding methods
Objective Explain how method overloading and overriding work.

Overloading and overriding Methods

Multiple methods of the same name but different signatures.
A method is overloaded in a class declaration when two or more methods have the same name but different parameters. That is, the methods differ in the number of parameters, types of parameters, or ordering of their parameter types. Examples of overloading are the println() methods of the java.io.PrintStream class.
Two methods may not be declared with the same name and parameter types but with different return types. This restriction also applies to methods that are inherited from superclasses. However, two methods with the same name and different parameter types may have different return types.
overloading: multiple methods of same name but diferent signatures
overloading: multiple methods of same name but diferent signatures
Advanced Overloading
Overriding
Overriding occurs when a method is declared with the same name, parameter types, and return type as a method that is inherited from one of its superclasses. Overriding allows a class to replace a superclass method with one of its own. The following restrictions apply to overriding:
  1. Methods that are declared as final may not be overridden.
  2. The overriding method must be as accessible as the overridden method. If the overridden method is public, then the overriding method must be public. If the overridden method is protected, then the overriding method must be public or protected. If the overridden method is declared with package access, then the overriding method must not be private.
  3. The overriding method may not throw any exceptions that are not covered by the throws clause of the overridden method.
  4. Static methods may not be overridden to be non-static.
Since private methods are not inherited, they may not be overridden.


Method in the superclass is overridden by the method in the subclass
Method overriding: Method in the superclass is overridden by the method in the subclass
Method Overriding and Exceptions

The superclass method is replaced, or overridden, in MyClass
The following class provides an example of overloading and overriding:
class Overriding extends Overridden {

  // display() is overloaded with three 
  // different method forms.
  void display() {
  }

  int display(int i) {
    return i;
  }
      
  // display(String s) overrides the
  // display(String str) method of
  // its superclass.
  void display(String s) {
  }

}

class Overridden {
	void display(String str) {
  }
}
Covariant Return Type