Chapter 1 Basic Computing and your first program

1
Chapter 1- Basic Computing and your first program
2
Overview

• Computer Basics
• Programming Basics
• Java Basics and your first program.

3
Computer Basics
4
Basic Computers and terms

• Computer is made up of two parts
• Hardware
• Physical equipment
• Monitor, keyboard, memory, hard disk, processor,
  mouse.
• Usually not changeable.
• Software
• The programs/information you run on the hardware.
  
• Operating Systems (Windows, Linux), applications
  (Word, Photoshop), and games.
• Modifiable.

5
Hardware components

• Monitor/Printer (Output)
• Shows what is happening in the computer.
• Keyboard/Mouse/Joystick (Input)
• Lets you interact with the computer
• CPU (Central Processing Unit)
• Brains of the computer.
• Receives input from the user, performs
  operations, and directs the output devices to
  display the results.

6
Hardware Storage

• We use storage to keep programs on our computer.
  It comes in many types
• Main memory Where most of the calculations are
  done, temporary, wiped out when the power is
  turned off.
• Hard Disk Where data is saved for more
  permanent storage (your files and directories are
  usually on your hard disk).
• Removable media Usually used for archiving
  information/backing up. Can consist of tapes,
  CD-Rs, removable hard disks, ZIP disks, or
  floppies (floppies bad).

7
Hardware storage How

• Information is stored on our computers in bits,
  or 1s and 0s.
• A byte is 8 bits, which used to be the length
  needed to store a single character (there were
  256 characters possible).
• The bytes are stored in a big list in memory, or
  on the hard drive. When I need a piece of
  information (say I open a midterm paper), the
  computer looks up its address in the list, and
  retrieves those 1s and 0s for me. The computer
  then interprets these bits and displays my paper.
  

8
Software

• Software consists of the programs that we run on
  the computer.
• Operating systems
• Applications
• Drivers
• When we combine programs with data or input, then
  we get some sort of results or output.

9
Software programming

• Software today is usually written in high-level
  languages, or programming languages that are
  easily read by humans. C/C, Java, Perl, VB
• Computers dont understand these languages, so
  programs have to be translated into lower-level
  languages for the computer. Machine-language,
  assembly
• Depending on when this translation is done, it
  is called compiling or interpreting.

10
Compiling/Interpreting
x x 1
00011101001001011000100101001011
Compiling
Interpreting
Object code Machine code
Source Program Source Code
11
Compiling vs. Interpreting

• Compiling
• Done before program is run.
• Translates the whole program at once.
• Takes longer to translate the program(compile).
• Finished program runs faster.
• Need to recompile for every new platform.

• Interpreting
• Done while program is run.
• Translates a single line at a time.
• Takes no time at all for any compilation.
• Finished program runs slower.
• No need to recompile for any new platforms.

12
How Java does it.

• Java uses a mixture of interpretation and
  compilation.
• Use the Java compiler to turn our high-level
  program into byte-code.
• To run the program, we then give the byte-code to
  the Java byte-code interpreter to run the code.
• This allows us to run our program on any OS that
  a Java byte-code interpreter has been created for
  (currently Windows, Linux, and Solaris) without
  having to recompile.

13
Large Java programs

• When programs get big, they are often done in
  multiple pieces, each in a separate file.
• Each file is separately compiled into its own
  piece of Java byte-code.
• Before you can run these large programs, the
  individual byte-code files need to be linked.
• Luckily for us, this is done behind-the-scenes
  for us, so we dont have to worry about it.

14
Programming Basics
15
How to go about creating a computer program

• Four main steps (in this class)
• Find out what you need to do (gather
  requirements).
• Figure out how youll do it (design).
• Do it (implement).
• Check to see if youve done it correctly (test).

16
Gather Requirements.

• Read the problem carefully!
• Read it twice if you have to.
• Figure out what it really wants.

17
Design

• Start off with an English description of what you
  want to do in general.
• Step by step, start adding more details to your
  description.
• Continue this until you can translate this
  description into Java code.

18
Design Example

• I want to write a program that converts
  temperatures.

• a program that converts Fahrenheit to Celsius.

• a program that
• gets a value in Fahrenheit
• converts that value to Celsius
• outputs the Celsius value to the screen.

• b. Celsius 5(degreesF 32)/9

19
Implement

• Translate your design into actual Java code.

20
Test

• Test your written program to make sure that is
  does all that the problem originally asked you to
  do.

21
Object Oriented Programming and Java.

• Java is heavily object oriented. In fact, almost
  everything we end up doing is with objects.
• Objects are the things that surround us books,
  cars, flashlights, etc.
• Methods are the actions that objects can perform.
  Cars can accelerate or turn, flashlights can turn
  on and off, etc.
• A class is a category of objects. Toyota Camry
  and Honda Accord both belong to the class of cars
  and to the class of automobiles.

22
Object Oriented Programming (OOP)

• Composed of three principles
• Encapsulation- I dont need to know how it works,
  just that it does.
• Polymorphism- The same word means different
  things to different people.
• Inheritance- You inherit characteristics from
  your ancestors.
• We will cover these more at a later time.

23
Your first Java program.
24
FirstProgram.java
public class FirstProgram public static
void main(String args)
System.out.println("Hello out there.")
System.out.println("Want to talk some more?")
System.out.println("Answer y for yes or n
for no.") char answerLetter
answerLetter SavitchIn.readLineNonwhiteChar()
if (answerLetter 'y')
System.out.println("Nice weather we are
having.") System.out.println("Good-bye.")
System.out.println("Press enter key to
end program.") String junk junk
SavitchIn.readLine()
25
Code explanation
public class FirstProgram public static
void main(String args)

• Always have nearly the same first two lines in
  every program for now. You will only change the
  class name (FirstProgram).
• Since it says public class FirstProgram you must
  save this in a file called FirstProgram.java .
• The beginning of the program is indicated by the
  main method.

26
Code Explanation
System.out.println("Hello out there.") System.out
.println("Want to talk some more?") System.out.pr
intln("Answer y for yes or n for no.")

• System.out.println tells the computer to write
  the upcoming message out to the monitor.
• When the program is run, these three lines will
  appear on the screen

Hello out there. Want to talk some more? Answer y
for yes or n for no.
27
Code Explanation
char answerLetter answerLetter
SavitchIn.readLineNonwhiteChar()

• Makes answerLetter a variable that can hold a
  single character.
• Second line waits until the user inputs a single
  character. When they do, it assigns (single equal
  sign) whatever the user pressed in the variable.

28
Code Explanation
if (answerLetter 'y') System.out.println(
"Nice weather we are having.")

• Checks to see if what is stored in answerLetter
  (what the user entered), is equal (double equal
  sign) to the letter y.
• If they are equal (if the user entered y) then
  it prints out the message about the weather. Else
  the weather message is not printed at all.

29
Code Explanation
System.out.println("Good-bye.") System.out.printl
n("Press enter key to end program.") String
junk junk SavitchIn.readLine()

• Prints out a few more lines and then waits for
  the user to press the enter key before ending the
  program.
• Depending on your computer, you may or may not
  need these last two lines. It prevents the
  computer from shutting the program down before
  the user gets a chance to see all of the output.

30
Code Explanation

• The ending curly brackets tell the computer that
  the program has ended. For every opening curly
  bracket (), you must have a closing curly
  bracket (). If you dont the computer will
  complain of an error.

31
Java rules of syntax

• Javas syntax is very picky.
• Dont forget the semicolons! They usually go at
  the end of every statement.
• Java is case sensitive. System and system are
  not the same thing in Java.

32
End of Chapter 1

• Computer Basics
• Programming Basics
• A first Java program.
• Any questions?