1. COMP 110: Introduction to Programming Tyler Johnson January 14, 2009 MWF 11:00AM-12:15PM Sitterson 014

2. COMP 110 Spring 20092 Announcements Hand in HW0 at the front of the room after class

3. COMP 110 Spring 20093 Questions?

4. COMP 110 Spring 20094 Today in COMP 110 Hardware and Memory Programs and Compiling Your first JAVA program!

5. COMP 110 Spring 20095 Before Programming Need to know basics of a computer If you drive a car you should know it runs on gasoline What’s in the box?

6. COMP 110 Spring 20096 Hardware vs. Software Hardware Physical machine CPU, Memory Software Set of instructions for the machine to execute

7. COMP 110 Spring 20097 Hardware ENIAC One of the first general purpose programmable computers Visit the computer museum in the first floor lobby of Sitterson Hall

8. COMP 110 Spring 20098 Hardware CPU (Central Processing Unit) Executes instructions specified by a programmer GHz - number of instructions per second, how fast is the computer Dual Core - multiple processing units per CPU

9. COMP 110 Spring 20099 Memory Holds data for the computer to process Main Memory (RAM – Random Access Memory) Used for intermediate calculations Used to store the current program itself! Expensive Auxiliary Memory (Secondary Memory) Disk drives, CDs, Flash drives Cheap

10. COMP 110 Spring 200910 Measuring Memory Measured in bytes For example 2 gigabytes (GB) of RAM Megabyte (MB) = 1 million (10 6 ) bytes (or 1,048,576 = 2 20 bytes) Gigabyte (GB) = 1 billion (10 9 ) bytes (or 1,073,741,824 = 2 30 bytes)

11. COMP 110 Spring 200911 What is a Byte? Data, such as numbers and keyboard characters are stored as series of bits A bit is a digit with value 1 or 0 Examples 00111010 is a byte with value 58 01000001 is a byte with value 65 01100001 is a byte with value 97 A byte is composed of 8 bits Just large enough to store a keyboard character

12. COMP 110 Spring 200912 Encoding Characters How to encode keyboard characters? Assign each character a number Example (ASCII) ( 01000001 ) 65 = A ( 01000010 ) 66 = B ( 01000011 ) 67 = C ….

13. COMP 110 Spring 200913 Main Memory Called RAM (Random Access Memory) Fast access Access any location in memory in constant time Addressable Every byte has an address that is used when writing or reading data to memory

14. COMP 110 Spring 200914 What is a Program? Set of instructions for a computer to follow Example instructions: Add two numbers Divide two numbers Store a number at a memory location

15. COMP 110 Spring 200915 Programs Programs take data as input and produce a useful result Example A spell-checking program takes a text file as input and produces a list of misspelled words as output InputProgramOutput

16. COMP 110 Spring 200916 Programming Languages Modern programming languages (Java, C/C++) are designed to be human-readable Called high-level languages Computers can’t understand high level languages A Compiler translates our human-readable program into a machine-readable program Compiler is a program as well!

17. COMP 110 Spring 200917 Role of Compilers Program Source Code Compiler Machine Code Human-readable, What you will be writing in this class Machine-readable, What the machine actually executes Note: Java uses a slightly different approach, which we’ll see later

18. COMP 110 Spring 200918 Human- vs Machine Readable A human-readable instruction to add two numbers a = b + c; The equivalent machine-readable instruction might look this! 00101101101100101010101101010101010001111 01010100101000101001011101001010101010101 101010100

19. COMP 110 Spring 200919 Review What we’ve covered so far Hardware & Memory Programs and Compiling Now let’s learn a bit about Java

20. COMP 110 Spring 200920 Java A high-level programming language Java source code is human-readable Originally envisioned as a programming language for home appliances Is now the language of choice for internet applications Example internet application using Java

21. COMP 110 Spring 200921 Java Java is an interpreted language Compiler produces bytecode instead of machine code Bytecode is not quite readable by any machine When a Java program is run, an interpreter translates the bytecode into machine code on-the- fly The Java interpreter is called the Java Virtual Machine (JVM)

22. COMP 110 Spring 200922 Compiling & Running Java Programs Java program Java compiler Bytecode program Bytecode interpreter (Java JVM) Machine code Compiling a Java program Running a Java program Human- readable Machine- readable Java JVM- readable

23. COMP 110 Spring 200923 Java Interpreter Why is Java interpreted? The short answer is portability Can run the same byte code on any machine! No need to recompile for Windows or Mac OS X Ideal for internet applications

24. COMP 110 Spring 200924 Your First Java Program Source code on the next slide Displays a welcome message Asks the user to input two numbers Displays the sum of the numbers

25. COMP 110 Spring 200925 Sample Java Program (Section 1.2) import java.util.Scanner; public class FirstProgram { public static void main(String[] args) { System.out.println("Hello out there."); System.out.println("I will add two numbers for you."); System.out.println("Enter two whole numbers on a line:"); int n1, n2; Scanner keyboard = new Scanner(System.in); n1 = keyboard.nextInt(); n2 = keyboard.nextInt(); System.out.println("The sum of those two numbers is"); System.out.println(n1 + n2); } }

26. COMP 110 Spring 200926 Importing Packages import java.util.Scanner; Tells the compiler that this program uses the class “Scanner” in the package “java.util” A class is a piece of code that we give a name to So that when the Scanner class is used later in the program, the compiler knows what we’re referring to A package is a library of classes that have already been defined for you “java.util” – for various utilities such as reading input from the keyboard

27. COMP 110 Spring 200927 Begin the Program public class FirstProgram { … } Begin the class “FirstProgram” A class is just a piece of code that we give a name to Everything within the curly braces will be part of “FirstProgram”

28. COMP 110 Spring 200928 Classes Java programs are rarely written as a single piece of code all in one file They are typically divided into separate pieces called classes For know, think of classes as pieces of Java code

29. COMP 110 Spring 200929 Main Method public static void main(String[] args) { … } Begin the method called “main” Everything between the curly braces is part of the method “main” Methods contain lines of code that actually perform some action (statements) The group of statements within a method make up the method body Every Java program has a method called main

30. COMP 110 Spring 200930 Program Set-Up So far we have import java.util.Scanner; public class FirstProgram { public static void main(String[] args) { …} As of yet, the code performs no action Now for the body of the “main” method where the action occurs

31. COMP 110 Spring 200931 Output to Screen System.out.println("Hello out there."); System.out.println("I will add two numbers for you."); System.out.println("Enter two whole numbers on a line:"); These statements prints what is in quotes out to the screen Example System.out.println("Hello out there."); Causes “Hello out there.” to be printed out to screen

32. COMP 110 Spring 200932 Methods and Objects What does “System.out.println” mean? “System.out” is an object Java programs use objects to perform actions The actions are defined by methods “println” is a method that prints a message to the screen The println method is part of the System.out object

33. COMP 110 Spring 200933 Invoking Methods on Objects myCar.start() airplane.land() System.out.println(“Hi”.) ObjectsMethods Argument

34. COMP 110 Spring 200934 Variable int n1, n2; Declares “n1” and “n2” as variables that will be used to store data int is the data type that will be used for n1 and n2 int indicates an integer (whole number)

35. COMP 110 Spring 200935 Create Scanner Object Scanner keyboard = new Scanner(System.in); Enables the program to read data from the keyboard Creates an object of Scanner class called “keyboard” Class Object Class

36. COMP 110 Spring 200936 Call Method on Object n1 = keyboard.nextInt(); Read an integer from the keyboard and store it in n1 Object Method Invoke/Call

37. COMP 110 Spring 200937 Output to Screen System.out.println("The sum of those two numbers is"); System.out.println(n1 + n2); Add n1 and n2 Print the sum to the screen

38. COMP 110 Spring 200938 Sample Java Program (Section 1.2) import java.util.Scanner; public class FirstProgram { public static void main(String[] args) { System.out.println("Hello out there."); System.out.println("I will add two numbers for you."); System.out.println("Enter two whole numbers on a line:"); int n1, n2; Scanner keyboard = new Scanner(System.in); n1 = keyboard.nextInt(); n2 = keyboard.nextInt(); System.out.println("The sum of those two numbers is"); System.out.println(n1 + n2); } }

39. COMP 110 Spring 200939 Friday Recitation jGRASP Your first Java program Bring Laptop (fully charged) Textbook Download Java Development Kit (JDK) and jGRASP before lab (see webpage) Finish reading Sections 1.1, 1.2

40. COMP 110 Spring 200940 Announcements Hand in HW0 at the front of the room after class