Introduction to Java

Introduction to Java

• Created by James Gosling in 1995 for Sun Microsystems
• A platform-independent programming language
• Follows the "Write once, Run anywhere" principle

Why Learn Java?

• Java is used in retail, banking, financial services, scientific research, Android development, Stock Market and Big Data
• Essential core technologies include Web Development, Frameworks, Continuous Testing and Android

Features of Java

• Simple and easy to learn
• Portable and platform independent
• Object-oriented where everything is an "object"
• Secure and prevents activities from untrusted sources by running programs inside the sandbox
• Supports Remote Method Invocation (RMI) to invoke methods of other programs across a network
• Dynamic programs used to verify and resolve accesses to objects at run time
• Robust code checks during compilation and run time, as well as handles memory allocation
• High performance achieved through bytecode, which can be translated to native machine code

Java Development Kit (JDK)

• Contains the Java Virtual Machine (JVM)
• Includes Java Class Libraries and Java Runtime Environment (JRE)

How Java Works

• Java source code (.java) is compiled by the Java Compiler into Java Bytecode (.class).
• Bytecode can move locally or through a network.
• The Run-time Environment Class Loader and Bytecode Verifier check the code.
• The Java Interpreter or Just-in-Time Compiler turns code into machine code.

Installation

• Download Java Platform (JDK) version 8 update 121 from Oracle's website.
• Set the permanent path of JDK by going to My Computer Properties, Advanced system setting, and select on Environment Variables.
• Path can be found in the bin folder inside JDK installed on your system (C:\Program Files\Java\jdk1.8.0_121\bin).
• An Eclipse Neon installer needs to be installed.

Data Types in Java

• Primitive: byte (1 byte), short (2 bytes), int (4 bytes), long (8 bytes), float (4 bytes), double (8 bytes), char (2 byte), and boolean (1 byte)

Data Operations in Java

• Arithmetic Operators: +, -, *, /, %
• Unary Operators: ++, --
• Relational Operators: <, <=, >, >=, !=, ==
• Logical Operators: &&, ||, !

Control Statements

• Control statements consist of Selection Statements, Iteration Statements and Jump Statements
• Selection Statements: if statement and switch statement and case statement
  • if statement Syntax example: if (condition){ statements 1 ...} else {statements 2...}
  • switch statement Syntax example switch(expression) {case value1: Statement1 break; case value2: Statement2 break;}
• Iteration Statements: execute repeatedly as long as the loop condition is true
  • Includes while, do while and for loops
  • do while statement Syntax: do {statements...} while (condition is True)
  • while statement Syntax: while (condition is True){ statements...}
  • for statement Syntax:for(initialization; condition; iteration){ statements...}
• Jump Statements: break and continue
  • break statement syntax: break;
  • continue statement syntax: continue;

Array in Java

• Arrays are data structures that hold sequential elements of the same type
• Can be of single or multiple dimensions
  • Single Dimensional Array example initialization: int a[] = new int[12]
  • Multi Dimensional Array example initialization: int table[][] = new int[4][5]

Object Oriented Programming

• An object oriented and class based programming language
• An Object is a collection of data (variables) and methods (functions) that act on said data
• A Class is a blueprint for the object.
• Inheritance is a mechanism through which one object acquires all the properties and behaviors of a parent object
• Helps avoid code redundancy, with a derived class is developed upon a base class to achieve code reusability
• Encapsulation is the mechanism that binds together code and the data it manipulates
  • Variables of a class will be hidden from other classes and can be accessed only through the methods of their current class
• Polymorphism is the ability of a variable, function or object to take on multiple forms.
  • Overloading of functions is achieved by the usage of polymorphism.
• Abstraction is the methodology of hiding the implementation details from the user and only providing the functionality to the users.
  • In Java, abstract class and interface can achieve abstraction.