Java Technology: The Basic Constructs In Java

Java Technology The Basic Constructs in Java

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Session Plan 

Concept of Object Oriented Programming



Java architecture



Rules of Java



Data types



Variables



Operators



Control statements

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References 

Patrick Naughton & Herbert Schildt, Java2: The Complete Reference 3rd Ed., Tata McGraw-ill Publishing Company Limited, New Delhi.

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Eckel & Bruce, Thinking in Java, 3rd Ed., Addison-Wesley.

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"The Java Tutorial", found online at http://java.sun.com/docs/books/tutorial/

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History of Java 

Java is an object-oriented programming language developed by James Gosling and colleagues at Sun Microsystems in the early 1990s.

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Java was started as a project called "Oak" by James Gosling in June 1991.

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The first public implementation was Java 1.0 in 1995.

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Introduction To Java 

A language developed at Sun Microsystems



A general-purpose language



High-level language



Developed initially for consumer devices

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Helps in building a dynamic Web



Supported today by most of the big players like IBM, Oracle etc.

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Features of Java 

Object-oriented



Simple



Robust



Secure



Architecture Neutral / Portable



Multithreaded



Distributed

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What is Java? 

Object Oriented Language



Platform Independent

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What is an Object? 

Objects are things 

PC Monitor, Employee, Space Shuttle, Complex Number, (X+Yi), Bank Account, Bicycle



Objects may be simple or complex



Objects may be real or imaginary

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Object Oriented Program Data

Data

Function

Function

Data

Data

Function

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Function

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Object Oriented Concepts Abstraction

Encapsulation

Oops concepts

Polymorphism

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Inheritance

Object Oriented Concepts 

Abstraction: 

The process of extracting the essential information and hiding the irrelevant details.



Encapsulation: 

The process of binding code and data together in the form of a single unit called class.

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Inheritance - Inheriting the properties of one object by another object

Inheritance

Single Inheritance

MultiLevel Inheritance

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Hybrid Inheritance

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Multiple Inheritance

Hierarchical Inheritance

Polymorphism - A form taking more than one action. Polymorphism

Run-Time Polymorphism

Compile Time Polymorphism

Overriding

Overloading

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Java Platform Independent 

A platform is the hardware or software environment in which a program runs

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Once compiled, code will run on any platform without recompiling or any kind of modification. “Write Once Run Anywhere”

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This is made possible by making use of a Java Virtual Machine (JVM)

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Java Platform Independent 

The Java VM is base for Java platform and is ported onto various hardware-based and OS based platforms.

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The JVM converts machine code into byte code and vice versa. This makes platform independence possible.

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The Java API is a large collection of ready-made, frequently used class libraries, stored in packages.

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The Java Environment Java Program JavaAPI API Java Java Virtual Machine

Native OS Platform

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Java Platfor m

Execution Plan: Source code File Compiler Byte code File Interpreter

JVM

JVM

JVM

Windows

Linux

Sun Solaris

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Structure of a Java Program Package Declaration Import Statements Class declaration Method Definitions Main Method

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A simple Java Program class hello { public static void main(String args[]) { System.out.println(“Welcome to Java”); } }

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Compilation,Execution of program

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Rules of Java 

The name of the file must always be the name of the “public class”

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It is 100% case sensitive

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You can have only one public class in a file (i.e. in one .java file)

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Every “stand alone” Java program must have a public static void main defined 

it is the starting point of the program.

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Java Keywords abstract

const

finally

implements

public

this

boolean

continue

for

instanceof

throw

transient

break

float

if

null

short

void

byte

default

import

int

super

volatile

case

do

false

return

switch

while

catch

double

interface

package

synchronized

char

else

long

private

static

class

extends

goto

protected

try

true

final

new

native

throws

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Data Types in Java 

Java is a Strongly typed language

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Two types of variables 

Primitive type

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Reference type

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null is a special type

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Reference types cannot be cast to primitive types

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Primitive Data Types in Java Type

In bits

Range

Byte

8

-27 to 27-1

Short

16

-215 to 215-1

Int

32

-231 to 231-1

Long

64

-263 to 263-1

Float

32

3.4e-038 to 3.4e+038

Double

64

1.7e-308 to 1.7e+308

Boolean

8

True/False

Char

16

0 to 65,636 (216-1)

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Reference Types in Java 

Arrays, classes, and interfaces are reference types



A reference is called a pointer, or a memory address in other languages The Java programming language does not support the explicit use of addresses like other languages do

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Variables in Java 

The variable is the basic unit of storage in a Java program

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The variables have a scope, which defines their visibility and lifetime

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The variable name is a name given to the memory location in a computer and not for the value present in it.



Member Variables



Automatic Variables

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Variables in Java 

Object Reference Variables

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Type Conversion and Casting 

Implicit (Automatic, non-explicit type changing is known as Conversion)

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Explicit (Casting)

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Widening conversions



Narrowing conversions are allowed in java

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Variable Types: Local Variables

Variables

Static variables

Instance variables

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Java Operators 





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Arithmetic Operators =,-,*,/,% Unary Arithmetic operators ++,-Relational operators >,<,>=,<=,==,!= Logical and Bitwise operators &&, ||, !, >>, <<, >>>, &, | Ternary operator ()?():()

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Control Structures in Java 

Similar to the “C” Programming Language

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Decision making - if-else, switch-case

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Loop - for, while, do-while

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Miscellaneous - Break, continue, label, return

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Arrays in Java 

Java arrays are objects



Array contains like-typed values

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Array can contain both primitive and reference data types

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When used with reference data types, reference (memory location) is only stored in arrays. They are nothing but ‘array of arrays’

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Arrays in Java 

Array Declaration -int my Integers[]; -int[] my Integers;

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Array memory allocation -int myIntegers[]=new int[10];

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Array Initialization -int my Integers[]={1,2,3,4,5};

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Summary 

OO Concepts



Features of Java



Architecture of Java



Structure of a Java Program



Compiling a Java Program



Executing a Java Program

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Summary 

Basic Language Rules



Syntax



Keywords in Java



Variables in Java



Operators in Java



Control Structures in Java

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