1. Introduction to Programming with Java, for Beginners Machine vs. Programming Language Intro to Java Edit-Compile-Run Program Process

2. 1 Outline What do computers understand? Machine Language vs. Programming Language Introduction to Java Process of Computer Programming Write, Compile and Run Java Program

3. 2 Recap A programming language a language that you can learn to write, and the computer can be made to understand We will learn Java in this course But before we jump into Java, lets know a computer a little bit

4. 3 What Computers are good at? Doing calculations and comparisons Producing the same answer every time Like calculating the sum of hundreds of numbers Storing information Mostly do not forget information Looking up information quickly Search through a phone book to find the customer name for a phone number

5. 4 Computer’s Anatomy Consists of: Central Processing Unit (CPU) a.k.a processor  Basically does all the calculation e.g. addition Memory  Stores Information (instructions or data)  RAM (volatile) and Hard Drive (Non-volatile) Input/Output Devices  Communicate with the outside world (e.g. keyboard, mouse)

6. 5 What does the Computer Understand? At the lowest level, a computer has electronic “plumbing” Operates by controlling the flow of electrons through very fast tiny electronic devices called transistors The devices react to presence or absence of voltage Could react actual voltages but designing electronics then becomes complex Symbolically we represent 1. Presence of voltage as “1” 2. Absence of voltage as “0”

7. 6 What does the Computer process & store? An electronic device can represent uniquely only one of two things Each “0” and Each “1” is referred to as a Binary Digit or Bit Fundament unit of information storage To represent more things we need more bits E.g. 2 bits can represent four unique things: 00, 01, 10, 11 k bits can distinguish 2 k distinct items Combination binary bits together can represent some information or data. E.g. 00101001 can be 1. Decimal value 41 2. Alphabet (or character) ‘A’ in ASCII notation 3. Command to be performed e.g. Performing Add operation

8. 7 Machine Language Computers understand only 0’s and 1’s A.k.a Machine Language Very tedious for “Humans” to deal with 0’s or 1’s

9. 8 Programming to Machine Language The compiler translates the programming language into a specific machine language Specific Machine: Electronic Hardware + Operating System e.g. Intel Process + Windows XP vs. Intel processor + Mac OS Once translated (Programming -> Machine) The same program cannot run on different machine Java avoids the above problem Code is portable - Write one run anywhere! One of the features for popularity of Java

10. 9 Java Compiler and Virtual Machine The Java Compiler Reads file with extension.java Checks syntax / grammar Creates a.class file which contains byte code (machine code) independent of any machine Java Byte Code Is portable The JVM(Java Virtual Machine) Translates byte code in to instructions for a particular processor, which “runs the program”

11. 10 Other Features of Java Has Graphical User Interface Capability Create interactive programs  Stand alone Java Applications that can be executed on any computer that has JVM Create Dynamic Web Pages  Java Applets are programs that can run in Browser (e.g. Internet Explorer or Firefox) that has Java Plugin  Java Servlets are programs that can run machines hooked up to internet (server) Gained popularity in gadgets such as PDAs, cell phones etc.

12. 11 Editions of Java Java SE “ Standard Edition” (currently at version 6.0) For desktop applications Java ME “Micro Edition” For gadgets such as smart phones or personal digital assistants Java EE “Enterprise Edition” For Java programs that run on web servers Website: http://java.sun.com/

13. 12 Things needed for Java Program JRE, Java Runtime Environment This is the software that allows you to run Java programs on your computer Called either “the JRE” or “the runtime” JDK, Java Development Kit The software that allows you to create and run Java programs on your computer When you install the SDK, you get a JRE along with it

14. 13 Java Books Online: See the Resources page on course website Java Backpack Reference Guide By Peter J. DePasquale Useful, concise reference Others An Introduction to Problem Solving and Programming” (4th Edition) by Walter Savitch Head First Java by Kathy Sierra and Bert Bates

15. 14 Process of Computer Programming To come up with a computation solution Remember that Rome was not built in one day!! Program in pieces, and test before writing the whole solution Edit (Syntax + Semantics) Compile Run (observe your output) Compile-time or Syntax Error Run-time or Semantic Error

16. 15 Process I Writing Programs Use any regular text editor Write Java style program and save the file as filename.java. Exercise on Linux OS: Save Hello.java in your directory from course website Open Terminal Window  Users interacted with the computer with terminal window before GUI  You should see: “username@ …>”

17. 16 Process I (contd..) Type “ls” to see contents of your disk ls is command that displays files & directory username@...> ls Type “cd” to change directory/folder where Hello.java is saved cd means change directory E.g. cd Desktop

18. 17 Process I (contd..) Compiling Java on a “Linux OS” Type: export PATH=/usr/java/jdk1.5.0_04/bin/  This tells xterm where to find the java compiler To compile type: javac Hello.java If no compiler errors you should see Hello.class in your program1 directory  To see whether your directory contains type “ls” Executing/Running your program At the command prompt type: java Hello You will find the word “Hello World” printed

19. 18 Process I (contd..) This process is not straight forward Need to know commands such as cd, ls  Commands can different on different Operating System e.g. On Windows “ls” is “dir” Regular text editors do no highlight or color certain features that tell us that this a java program  There are better editors that highlight the language syntax

20. 19 Process II Simpler way!! Use Integrated Development Environment (IDE) Another software program that makes it easier to write, compile and run programs We’re going to use the free Dr. Java IDE Activity Dr Java Tutorial