13 X 11 Java Lecture 1 CS 1311 Introduction 13 X 11.

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Java Lecture 1

CS 1311

Introduction

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Serious Stuff

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Put these in order

• Avoid damage to equipment and material• Get the job done• Avoid injuries• Maintain good community relations

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Normal World

• Avoid injuries• Avoid damage to equipment and material• Get the job done• Maintain good community relations

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Military@War

• Get the job done • Avoid injuries• Avoid damage to equipment and material• Maintain good community relations

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Ballistics

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Ballistics

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Ballistics

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Ballistics

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Ballistics

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Ballistics

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Ballistics

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Assumptions• Flat non-rotating earth• Vacuum• Constant gravity

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Ballistics Calculations

• Required rooms full of mathematicians• Very slow, tedious work• Anything that would help could help to win the war

• Money no object• Commercialization not considered• Software Engineering?

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Let's invent a computer

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Computer Programming

• Initially by hand• Big breakthrough: Machine translation• Analysis of computation• Church-Turing

Functional Imperative/Procedural

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Paradigm Review

• Functional Programming– Mathematical base– Provably correct– Disassociated from machine model

• Imperative/Procedural Programming– Machine oriented– Mathematical ties

• Object Oriented Programming– Some features of both– Result of industry maturation & growth

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Origins of OO

• USAF ATC Randolph AFB B220

Locations

Routines

Data

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Origins of OO

• USAF ATC Randolph AFB B220• Simulation

MachinesWorkers

Products

Conveyor

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Origins of OO

• USAF ATC Randolph AFB B220• Simulation• Large scale projects

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Origins of OO

• USAF ATC Randolph AFB B220• Simulation• Large scale projects• GUI's

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So what is it?

• A brief overview• My favorite example

Queue

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Chez Guillaume

• Application to maintain 2 queues• Allow adding to either list• Allow removing from either list

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How might it be done?

Enqueue Module

Dequeue Module

isEmpty Module

head.tailRestaurant Module

head.tail Input Module

Output Module

Menu Module

Data Structure

Data Structure

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How might it be done?

Enqueue Module

Dequeue Module

isEmpty Module

head.tailRestaurant Module

head.tail Input Module

Output Module

Menu Module

Data Structure

Data Structure

Where isthe queue?

The OO ApproachRestaurant Object

Input Module

Output Module

Menu Module

Data Objects

Queue Object

Enqueue Module

Dequeue Module

isEmpty Module

head.tail

Queue Object

head.tail

Enqueue Module

Dequeue Module

isEmpty Module

Data Object

Get Data Module

Set Data Module

Cust Data

Ref

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The OO Approach

• Why do we want a new language?

• Why do we want to arrange things in such a fashion?

• What are the goals?

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Goals

• Encapsulation• Reusability• Adaptability/Flexibility• Decentralization/Distribution

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OOP Terminology

• Abstract Data Type• Class• Object• Method• Fields/Attributes• References

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Characteristics of OOP Language

• Everything is an object• A program is a bunch of objects telling each other

what to do by sending each other messages• Each object has its own memory made up of other

objects• Every object has a type which in OO terms means

that every object is an instance of some class• All objects of a particular type can receive the

same messages. An object of type circle will also be an object of type shape thus...

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Java

• Toasters• Smart cards• Killer apps• The wwweb

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Java, the good news

• Real• Very powerful• In demand• Software engineering• Universal

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Java, the bad news

• Real• Very powerful• Not an educational language• Jack of all trades/Master of none• Slow

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Clever Java Stuff

• Java program can be run by web browser• Borrowed a lot of syntax from c and c++• Give it away• WORA• Security

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Translation

• Compilation– Fortran– Cobol– Pascal– Algol– C/C++

• Interpretation– Basic– Lisp– Scheme

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Emulation

• How to sell a new computer to someone with lots of software?

• Emulate the old hardware!

OldSoftware

New Computer

ProgramEmulating

Old Computer

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The Java Approach

• Compilation into ByteCode

JavaSource

ByteCode

Javac Compiler

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The Java Approach

• Interpretation by the Java Virtual Machine

Any Computer

JavaVirtual

Machine

ByteCode

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Why is this cool?

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The Internet©Al Gore

JavaSource

ByteCode

Javac Compiler

Do this once

Web Server

Your Computer

Your Favorite Browser

JavaVirtual

Machine

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“Source Code” [.java]

Javacompiler

Generic“Byte Code” [.class]

OS-specificJVM

interpreter

Executeprogram

Compilation/Execution

Need one of these for every different

OS

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Sample Application

public class HelloWorld

{

public static void main(String argv[])

{

System.out.println(“Hello World!”);

}

}

We create a file (using an editor) called “HelloWorld.java”

We compile by typing (at the OS prompt):

javac HelloWorld.java

Which produces HelloWorld.class

Then we execute by typing:

java HelloWorld

Hello World!

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Demo

>javac HelloWorld.java

>java HelloWorld

Hello World!

>

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Quick Trix

• The name of the file must match the name of the class EXACTLY!!!• File: Bubba.java• Contains:

• Everything must be EXACTLY correct!!!

class Bubba{...

Capitalization counts

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A Final Word

• static• static is a source of great confusion and

sometimes even frustration• Here's the basic idea (don't worry if this is

confusing we'll explain it again• and again• and again• and again

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Java Structure

• Java programs consist entirely of files containing classes

• Classes are like blueprints or templates• They describe the structure and operation of

objects.• Objects are like whatever is made from a

blueprints or template.• Objects are considered to be dynamic• Sometimes there is a need for something to not

be dynamic hence you may declare it static.

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Questions?

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