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Lecture 10


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Notes on core java

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Lecture 10

  1. 1. Core Java Debasish Pratihari Inheritance :   Object oriented programming allows classes to inherit commonly used state and behavior from other class through inheritance. Allows a class to acquire the members of another class.  Parent-child/super-sub relationship is established.  Child can not restrict the scope of inheritance.  By default java classes are sub class of Object class directly or indirectly.  Java does not supports multiple inheritance. Parent/super decide the members that can be inherited by access specifiers.  Note:  Java uses a keyword extends to inherit.  Primarily solves two purposes. Re-usability and Providing a generic behavior.  A super class reference can refer to any object of its subclass.  If signature of a function in the super class is same as the signature of a function in the sub-class then the function is said to be over-ridden and it can’t be called by the object of sub class.  Any other class reference can be assigned to Object Class object.   If a function is declared as final it can’t be over-ridden. Incase of a child class member having the same name as of a parent class member then the parent class member is suppresses. And then to call those parent class members we have to use the super keyword.   If a class is final then it is restricted to be inherited. Compiler attaches a word super() as the first line of the constructor by default which calls the no-args constructor of the parent.  Note : Super object always holds address/reference of parent class. Lecture/core/oops3/10 Page #1 feel the Technology…
  2. 2. Core Java Debasish Pratihari Abstract Class:  An abstract class is specifically designed to be inherited only. i.e. it can’t be instantiated. However it can be used to create object reference.  A class can be made Abstract by using the keyword “abstract”  If a class contains any abstract method then it must be declared as abstract.  A abstract class may have fully defined methods (concrete methods) also. Abstract Method:  Abstract methods are not concrete methods.  They need to be override by the subclasses.  An abstract method force to declare its class as abstract. Example : abstract class Shape{ abstract void getData(); void aboutUs(){ System.out.println(“Developed by Debasish at Lakshya”); } } class Circle extends Shape{ void getData(){ //method definition here } } Lecture/core/oops3/10 Page #2 feel the Technology…
  3. 3. Core Java Debasish Pratihari Interface:  Using the keyword interface, you can fully abstract a class interface from its implementation.  Using interface, you can specify what a class must do, but not how it does it.  Interfaces are lack of instance variable, and their methods are declared without any body  A class can implement any number of interfaces  To implement an interface, a class must create a complete set of methods defined by the interface.  All the variables of an interface are public, static and final .All methods are abstract.  The methods of a class that implements can interface must be declared public.  It is both permissible and common for classes that implement interfaces to define additional members of their own.  You can declare variables as object reference that uses an interface rather than a class type. Any instance of any class that implements the declared interface can be referred to by such variable.  An interface reference variable only has knowledge of the methods declared by its interface declaration  If a class includes an interface but does not fully implement the methods defined by that interface, than that class must be declared as abstract  One interface can inherit another interface by use of the keyword extends.  When a class implements an interface that inherits another interface, it must provide implementation for all the methods defined within the interface inheritance chain. Lecture/core/oops3/10 Page #3 feel the Technology…
  4. 4. Core Java Debasish Pratihari Nested, Inner and Anonymous Classes:  A class can be defined inside another class, called nested class.  Its scope is limited within its enclosing class.  A nested class can access all the members of its enclosing class including private members. But the enclosing class can’t access any member of the nested class.  The nested class can be static or non-static  A static nested class can access the members of its enclosing class by instantiating it.  An inner class is a non-static nested class.  The natural application for inner class is to declare classes that are used only inside some other class or that are closely related to another.  Inner classes may declare only compile time constant fields.  inner and anonymous classes can make your Java code easier to understand and maintain. They keep related classes in the same source file and avoid the proliferation of very small classes  Non-static inner classes have some limitations, though. Specifically, they cannot declare static initializers and static members, except in constant fields. Besides that, inner classes declared inside methods cannot access the method’s local variables and parameters, unless they are declared final.  Inner-Anonymous classes are classes that don’t have a name (hence the term anonymous). Because they don’t have a name, there is no way to refer to them. For this reason, their declaration must be given at creation time, as part of the new statement.  Technically, anonymous classes are considered nonstatic inner classes, so they have the same privileges and limitations of non-static inner classes declared inside a method. Lecture/core/oops3/10 Page #4 feel the Technology…