The Joy of Programming

(also known as)

Introduction to Object-Oriented Programming

Resources• Java in a Nutshell from O’Reilly

• Java Standard Edition (JSE) download

http://www.oracle.com/technetwork/java/javase/downloads/index.html(download the SDK, not the JRE; you may not want it bundled with

NetBeans; you can also download the documentation from this link)

• Java API Documentationhttp://docs.oracle.com/javase/7/docs/api/

• Java Tutorialhttp://docs.oracle.com/javase/tutorial/index.html

• Lots of other stuffhttp://www.oracle.com/technetwork/java/javase/overview/index.html

What is a computer?

memoryprocessor disk

I/Odevices

data

instructions

Programming Languages• assembled languages

// X = (A+B) * (C+D)

LR 1, A // load register 1 from A

AR 1, B // add B to register 1

LR 2, C // load register 2 from C

AR 2, D // add D to register 2

MP 2, #1 // multiply register 2 by register 1

SR 2, X // store register 2 in X

• compiled languages (Fortran, Cobol)X = (A + B) * (C + D)

• structured languages (C, Pascal)

Programming Languages (cont.)• object-oriented languages (C++, Ada, Smalltalk,

Java)

• 4th generation languages: special purpose (RPG, DBASE, Delphi)– databases– proprietary products

• visual programming environments /integrated development environments (Visual Basic, Visual C++, JBuilder, Eclipse)

Compiled vs. Interpreted• Compiled Languages

source code => compiler => relocatable object code =>

loader => absolute code– source code is portable (sort of)– object code is platform-specific

• Interpreted Languages (Java)source code=> compiler => bytecode => interpreter =>

absolute code on the fly– bytecode is portable to any platform with an interpreter– interpreting is slower

Java• an object oriented language

• an interpreted language

• developed by Sun MicroSystems

• versions:– JDK v1.7.x

• available free from Oracle:http://www.oracle.com/technetwork/java/javase/downloads/index.html

Applications vs. Applets• A program which runs directly on the computer is

called an application

• programs may also be downloaded from the web and run in a browser; these are called applets

• applets are an outgrowth of Java’s platform independence, which allows an applet to run in a browser on any machine (PC, MAC, UNIX, …)

• applets are subject to security restrictions:– they cannot read or write the local hard drive– they cannot print– they can only talk to the computer that served them

Java Structure• The basic programming element in Java is the class

• every class has a name

• all instructions and data in Java exist in a class

• classes usually contain methods, which also have a name

• all instructions in Java exist in a method inside a class (almost)

Application Mechanics• write a class in a text editor; save it to a file with the same

name as the class and a .java suffix• set the path:

– In the MS-DOS Prompt window set path=%path%;c:\jdk1.4\bin

– Windows98, etc.:in C:Autoexec.bat (save the original first)

– WindowsXP: Control Panel > System > Advanced > Environment Variables > select Path under System Variables > Edit

• compile the file in an MS-DOS Prompt window: javac MyProgram.java

• run the class in an MS-DOS Prompt window:java MyProgram

Applet Mechanics• write a class that extends Applet in a text editor;

save it to a file with the same name as the class and a .java suffix

• compile in an MS-DOS Prompt window: javac MyApplet.java

• write an html program to load the applet; save it to a file with .html suffix

• load the html file in a browser, or via appletviewer in an MS-DOS Prompt window:

appletviewer MyApplet.html

• applets usually involve a graphical display, and/or some interaction with the user (GUI)

Hello World Application// the HelloWorld class, in file HelloWorld.javapublic class HelloWorld{ // the main method public static void main (String[] args) { System.out.println (“Hello World!”); }}

– class– method definition– method invocation– method parameters/Strings– comments– keywords (in blue)– curly braces/indentation

Hello World Appletimport java.applet.*;

import java.awt.*;

// the HelloWorldApplet class

// (saved as HelloWorldApplet.java)

public class HelloWorldApplet extends Applet

{

// the paint method

public void paint (Graphics g)

{

g.drawString (“Hello World!”, 20, 20);

}

}

Hello World Applet (cont.)• the HTML, saved as HelloWorldApplet.html

<HTML>

<HEAD>

<TITLE>First Applet</TITLE>

</HEAD><BODY> <APPLET code=HelloWorldApplet.class

width=200 height=100> </APPLET></BODY>

</HTML>

Edit program

Compile program

Compilererrors?

Run program

Exceptions?IncorrectResults?

yes

yes

ProgramDevelopmentProcess

Algorithms

• A procedure which is– unambiguous– executable– terminating

• Example: IRS Form 1040

• computer programs implement algorithms

• you must understand the algorithm before it can be programmed