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Object Oriented Programming - Part 2


What is method overloading ?

Method Overloading means to have two or more methods with same name in the same class with different arguments. The benefit of method overloading is that it allows you to implement methods that support the same semantic operation but differ by argument number or type. Note:
  • Overloaded methods MUST change the argument list
  • Overloaded methods CAN change the return type
  • Overloaded methods CAN change the access modifier
  • Overloaded methods CAN declare new or broader checked exceptions
  • A method can be overloaded in the same class or in a subclass

    What is method overriding ?

    Method overriding occurs when sub class declares a method that has the same type arguments as a method declared by one of its superclass. The key benefit of overriding is the ability to define behavior thatís specific to a particular subclass type. Note:
  • The overriding method cannot have a more restrictive access modifier than the method being overridden (Ex: You canít override a method marked public and make it protected).
  • You cannot override a method marked final
  • You cannot override a method marked static

    What are the differences between method overloading and method overriding ?

    Overloaded Method Overridden Method
    Arguments Must change Must not change
    Return type Can change Canít change except for covariant returns
    Exceptions Can change Can reduce or eliminate. Must not throw new or broader checked exceptions
    Access Can change Must not make more restrictive (can be less restrictive)
    Invocation Reference type determines which overloaded version is selected. Happens at compile time. Object type determines which method is selected. Happens at runtime.

    Can overloaded methods be override too ?

    Yes, derived classes still can override the overloaded methods. Polymorphism can still happen. Compiler will not binding the method calls since it is overloaded, because it might be overridden now or in the future.

    Is it possible to override the main method ?

    NO, because main is a static method. A static method can't be overridden in Java.

    How to invoke a superclass version of an Overridden method ?

    To invoke a superclass method that has been overridden in a subclass, you must either call the method directly through a superclass instance, or use the super prefix in the subclass itself. From the point of the view of the subclass, the super prefix provides an explicit reference to the superclass' implementation of the method.

    What is super ?

    super is a keyword which is used to access the method or member variables from the superclass. If a method hides one of the member variables in its superclass, the method can refer to the hidden variable through the use of the super keyword. In the same way, if a method overrides one of the methods in its superclass, the method can invoke the overridden method through the use of the super keyword.

    How do you prevent a method from being overridden ?

    To prevent a specific method from being overridden in a subclass, use the final modifier on the method declaration, which means "this is the final implementation of this method", the end of its inheritance hierarchy.

    What is an Interface ?

    An interface is a description of a set of methods that conforming implementing classes must have. Note:
  • You canít mark an interface as final.
  • Interface variables must be static.
  • An Interface cannot extend anything but another interfaces.

    Can we instantiate an interface ?

    You canít instantiate an interface directly, but you can instantiate a class that implements an interface.

    Object Oriented Programming - Part 3 >>>




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