Internet and Web Technology (CLASS-15) [JAVA Basics] | NIC/NIELIT Web Technology

Internet and Web Technology (CLASS-15) [JAVA Basics] | NIC/NIELIT Web Technology

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  Ayes Chinmay Internet & Web Technology (JAVA)
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  IWT Syllabus: Module 4: JavaProgramming OOP Fundamentals, Evolution of Java Programming Language, Basic Elements of Java Program, Class Fundamentals, Taking Input from Keyboard, Arrays in Java, Inheritance, Interfaces.
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  JAVA: Java is ahigh-level programming language originally developed by Sun Microsystems and released in 1995. It promised Write Once, Run Anywhere (WORA), providing no-cost run-times on popular platforms. Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX. James Gosling is known as the father of Java. Before Java, its name was Oak. Since Oak was already a registered company, so James Gosling and his team changed the Oak name to Java. James Gosling
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  Platform Dependent vsPlatform Independent : [Intialization] OS/Hardware machine code C source code gcc myprog.exe JVM bytecodeJava source code myprog.java javac myprog.class OS/Hardware Platform Dependent Platform Independent
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  JAVA Architecture:
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  JAVA Syntax:  Public:It is an Access modifier, which specifies from where and who can access the method. Making the main() method public makes it globally available. It is made public so that JVM can invoke it from outside the class as it is not present in the current class.  Static: It is a keyword which is when associated with a method, makes it a class related method. The main() method is static so that JVM can invoke it without instantiating the class. This also saves the unnecessary wastage of memory which would have been used by the object declared only for calling the main() method by the JVM.  Void: It is a keyword and used to specify that a method doesn’t return anything. As main() method doesn’t return anything, its return type is void. As soon as the main() method terminates, the java program terminates too. Hence, it doesn’t make any sense to return from main() method as JVM can’t do anything with the return value of it.  main: It is the name of Java main method. It is the identifier that the JVM looks for as the starting point of the java program. It’s not a keyword.  String[] args: It stores Java command line arguments and is an array of type java.lang.String class. Here, the name of the String array is args but it is not fixed and user can use any name in place of it. class Test { public static void main(String[] args) { System.out.println("Hello"); } } Test.java
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  OOPs Concepts inJava:
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  OOPs Concepts inJava: (Cont.) CLASS: A class is a user defined blueprint or prototype from which objects are created. It represents the set of properties or methods that are common to all objects of one type. In general, class declarations can include these components, in order:  Modifiers: A class can be public or has default access  Class name: The name should begin with a initial letter (capitalized by convention).  Superclass(if any): The name of the class’s parent (superclass), if any, preceded by the keyword extends. A class can only extend (subclass) one parent.  Interfaces(if any): A comma-separated list of interfaces implemented by the class, if any, preceded by the keyword implements. A class can implement more than one interface.  Body: The class body surrounded by braces, { }.
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  OOPs Concepts inJava: (Cont.) OBJECT: It is a basic unit of Object Oriented Programming and represents the real life entities. A typical Java program creates many objects, which as you know, interact by invoking methods. An object consists of:  State : It is represented by attributes of an object. It also reflects the properties of an object.  Behavior : It is represented by methods of an object. It also reflects the response of an object with other objects.  Identity : It gives a unique name to an object and enables one object to interact with other objects.  Example of an object: dog
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  OOPs Concepts inJava: (Cont.) Encapsulation: Encapsulation is defined as the wrapping up of data under a single unit. It is the mechanism that binds together code and the data it manipulates. Another way to think about encapsulation is, it is a protective shield that prevents the data from being accessed by the code outside this shield.  Technically in encapsulation, the variables or data of a class is hidden from any other class and can be accessed only through any member function of own class in which they are declared.  As in encapsulation, the data in a class is hidden from other classes, so it is also known as data-hiding.  Encapsulation can be achieved by Declaring all the variables in the class as private and writing public methods in the class to set and get the values of variables.
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  OOPs Concepts inJava: (Cont.) Inheritance: Inheritance is an important pillar of OOP(Object Oriented Programming). It is the mechanism in java by which one class is allow to inherit the features(fields and methods) of another class. Important terminology:  Super Class: The class whose features are inherited is known as superclass(or a base class or a parent class).  Sub Class: The class that inherits the other class is known as subclass(or a derived class, extended class, or child class). The subclass can add its own fields and methods in addition to the superclass fields and methods.  Reusability: Inheritance supports the concept of “reusability”, i.e. when we want to create a new class and there is already a class that includes some of the code that we want, we can derive our new class from the existing class. By doing this, we are reusing the fields and methods of the existing class.  The keyword used for inheritance is extends.
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  OOPs Concepts inJava: (Cont.)
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  OOPs Concepts inJava: (Cont.)  Polymorphism: Polymorphism refers to the ability of OOPs programming languages to differentiate between entities with the same name efficiently. This is done by Java with the help of the signature and declaration of these entities. Polymorphism in Java are mainly of 2 types: 1. Overloading in Java 2. Overriding in Java
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  OOPs Concepts inJava: (Cont.) Abstraction: Data Abstraction is the property by virtue of which only the essential details are displayed to the user. The trivial or the non-essentials units are not displayed to the user. Ex: A car is viewed as a car rather than its individual components. Data Abstraction may also be defined as the process of identifying only the required characteristics of an object ignoring the irrelevant details. The properties and behaviours of an object differentiate it from other objects of similar type and also help in classifying/grouping the objects. Consider a real-life example of a man driving a car. The man only knows that pressing the accelerators will increase the speed of car or applying brakes will stop the car but he does not know about how on pressing the accelerator the speed is actually increasing, he does not know about the inner mechanism of the car or the implementation of accelerator, brakes etc in the car. This is what abstraction is. In java, abstraction is achieved by interfaces and abstract classes. We can achieve 100% abstraction using interfaces.
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  JAVA Sample Code: publicclass Test1 { public static void main(String[] args) { String name = "John"; System.out.println(name); } } Test1.java public class Test2 { public static void main(String[] args) { int myNum = 5; float myFloatNum = 5.99f; char myLetter = 'D'; boolean myBool = true; String myText = "Hello"; System.out.println(myNum); System.out.println(myFloatNum); System.out.println(myLetter); System.out.println(myBool); System.out.println(myText); } } Test2.java
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  Model Questions: 1. Whichof the following tag in HTML is used to surround information, such as signature of the person who created the page ? a) <body></body> b) <address></address> c) <strong></strong> d) <em></em> (UGC NET CS 2016) 2. Apache Tomcat is a a) Servlet b) Java Program c) Web Server d) Web Server that is capable of running java programs (APPSC - 2016)
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  Model Questions: (Cont.) 3.In Javascript, What dose in NAN function do ? (a) Return true, if the argument is not a number (b) Return false, if the argument is not a number (c) Return true, if the argument is a number (d) None of the given options 4. An alternative to JavaScript is (a) ASP .NET (b) JSP (c) VBScript (d) None of the given options (APPSC - 2016) (APPSC - 2016)
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  Next Class: Class Fundamentals