Inheritance polymorphism-in-java
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The document discusses inheritance and polymorphism in Java object-oriented programming, explaining key concepts such as the creation of subclasses from superclasses, calling superclass constructors, method overriding, and the use of protected members. It emphasizes the code reusability provided by inheritance and outlines how access modifiers affect member visibility. Additionally, it highlights the significance of abstract classes and interfaces in Java programming.
Inheritance polymorphism-in-java
- 1. INHERITANCE AND POLYMORPHISM IN JAVA Object-Oriented Programming www.beginwithjava.comwww.beginwithjava.com
- 2. WHAT YOU SHOULD LEARN www.beginwithjava.com What Is Inheritance? Calling the Superclass Constructor Overriding Methods Protected Member Multilevel Inheritance Polymorphism Abstract Classes and Abstract Method Interfaces
- 3. WHAT IS INHERITANCE Inheritance is the mechanism that allows programmers to create new classes from existing class. By using inheritance programmers can re-use code they've already written. Any new class that you create from an existing class is called sub class; existing class is called super class. www.beginwithjava.com
- 5. The complete program of above diagram is available at : www.beginwithjava.com The sub class gets all of the methods and state variables of the super class by default. The sub class can add new methods and state variables.
- 6. CALLING THE SUPER CLASS CONSTRUCTOR A subclass can have its own private data members, so a subclass can also have its own constructors. The constructors of the subclass can initialize only the instance variables of the subclass. When a subclass object is instantiated the subclass object must also automatically execute one of the constructors of the super class. To call a super class constructor the super keyword is used. www.beginwithjava.com The complete example program is available at : www.beginwithjava.com
- 7. OVERRIDING SUPER CLASS METHODS In a class hierarchy, when a method in a subclass has the same name and type signature as a method in its super class, then the method in the subclass is said to override the method in the super class. The version of the method defined by the super class will be hidden inside subclass. www.beginwithjava.com
- 8. The complete example program is available at : www.beginwithjava.com
- 9. PROTECTED MEMBER The private members of a class cannot be directly accessed outside the class. Only methods of that class can access the private members directly. However, sometimes it may be necessary for a subclass to access a private member of a super class. If you make a private member public, then anyone can access that member. So, if a member of a super class needs to be (directly) accessed in a subclass and yet still prevent its direct access outside the class, you must declare that member protected. www.beginwithjava.com Modifier Class Subclass World public Y Y Y protected Y Y N private Y N N