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The process of obtaining the data members and methods from one class to another class is known as inheritance. It is one of the fundamental features of object-oriented programming.

Important points

• In the inheritance the class which is give data members and methods is known as base or super or parent class.
• The class which is taking the data members and methods is known as sub or derived or child class.
• The data members and methods of a class are known as features.
• The concept of inheritance is also known as re-usability or extendable classes or sub classing or derivation.
  

  
  Why use Inheritance ?

  • For Method Overriding (used for Runtime Polymorphism).
  • It's main uses are to enable polymorphism and to be able to reuse code for different classes by putting it in a common super class
  • For code Re-usability
    
    

Advantage of inheritance

If we develop any application using concept of Inheritance than that application have following advantages,

• Application development time is less.
• Application take less memory.
• Application execution time is less.
• Application performance is enhance (improved).
• Redundancy (repetition) of the code is reduced or minimized so that we get consistence results and less storage cost.
  
  

  Types of Inheritance

  Based on number of ways inheriting the feature of base class into derived class we have five types of inheritance; they are:

  • Single inheritance
  • Multiple inheritance
  • Hierarchical inheritance
  • Multilevel inheritance
  • Hybrid inheritance
    
    

    Single inheritance

    In single inheritance there exists single base class and single derived class.

    Example of Single Inheritance :

    

    Output :  Salary is: 30000.0
                   Bonous is:  2000.0

    Multilevel inheritances in Java

    In Multilevel inheritances there exists single base class, single derived class and multiple intermediate base classes.

    Single base class + single derived class + multiple intermediate base classes.

    Intermediate base classes

    An intermediate base class is one in one context with access derived class and in another context same class access base class.

    

    Output  :  

    Total Salary is:  37000.0

    Multiple inheritance

    In multiple inheritance there exist multiple classes and singel derived class.

    The concept of multiple inheritance is not supported in java through concept of classes but it can be supported through the concept of interface.

    Hybrid inheritance

    Combination of any inheritance type

    In the combination if one of the combination is multiple inheritance then the inherited combination is not supported by java through the classes concept but it can be supported through the concept of interface.

    Important Points for Inheritance:

    • In java programming one derived class can extends only one base class because java programming does not support multiple inheritance through the concept of classes, but it can be supported through the concept of Interface.
    • Whenever we develop any inheritance application first create an object of bottom most derived class but not for top most base class.
    • When we create an object of bottom most derived class, first we get the memory space for the data members of top most base class, and then we get the memory space for data member of other bottom most derived class.
    • Bottom most derived class contains logical appearance for the data members of all top most base classes.
    • If we do not want to give the features of base class to the derived class then the definition of the base class must be preceded by final hence final base classes are not reusable or not inheritable.
    • If we are do not want to give some of the features of base class to derived class than such features of base class must be as private hence private features of base class are not inheritable or accessible in derived class.
    • Data members and methods of a base class can be inherited into the derived class but constructors of base class can not be inherited because every constructor of a class is made for initializing its own data members but not made for initializing the data members of other classes.
    • An object of base class can contain details about features of same class but an object of base class never contains the details about special features of its derived class (this concept is known as scope of base class object).
    • For each and every class in java there exists an implicit predefined super class called java.lang.Object. because it providers garbage collection facilities to its sub classes for collecting un-used memory space and improved the performance of java application.

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