1. Computer Programming Methodology Introduction to Java
COS 130
Computer Programming Methodology
Introduction to Java

2. Sign in sheet

3. Algorithm Like a Recipe, but . . . Strictly defines the order of steps
“In mathematics and computing, an algorithm is a procedure (a finite set of well-defined instructions) for accomplishing some task which, given an initial state, will terminate in a defined end-state.” - Wikipedia
Like a Recipe, but . . .
Strictly defines the order of steps

4. Program “A computer program is a list of instructions
to be executed by the computer.”
- Wikipedia
Programs implement algorithms
Programs are executable by “machines”
Programs group instructions into a unit of work

5. Programs Exist in 2 Forms
Source
Designed to be understood by people
Letters, words
Executable
Designed to drive the computer
Binary – 1’s and 0’s

6. Computing a 2 Step Process
Compilation
Compiler
Source
Executable
Execution
Executable
Computer
Data In
Data Out

7. Java Recent language developed by Sun
Primarily OO, procedural programming also supported (somewhat awkwardly)
Most “popular” computer language
Tiobe Software’s TPC index (
Write once, run everywhere

8. First Java Program
A name you pick
Capitalization important
Must call file the same name
public class Hello { public static void main(String args[]) System.out.println(“Hello World”); }
Starts a java file
All code inside class
We will only use 1
Braces group code
They always come in pairs
Special Method
Your program starts running here
Make it just like this
We will always have exactly one
An instruction to print something
Your program will do this
Statements always end in a semicolon
Or a brace

9. Literals Do not change while program is running
Must edit and re-compile program to change

10. Note: ‘A’ is not the same as “A”
Literals (cont.)
String Literal
Group of characters (letters)
Inside quotes
“Hello World”
Character Literals
One character (letter)
Inside single quotes
Example: ‘A’
Note: ‘A’ is not the same as “A”

11. Literals (cont) Integer Literals Floating Point Literals
Numbers with no decimal point
Just by itself
Example: 7
Floating Point Literals
Numbers with a decimal point
Example: 3.14
Note: 7 is not the same as 7.0
Note: 7 is not the same as “7”
Note: 7 is not the same as ‘7’

12. Variable Declarations
Sets aside space in memory
Labels the space with a name
Declaration sets variable for a particular type – numbers, letters, etc.
Once type is set it can not be changed
Variable must be declared before it can be used

13. Name rules First letter: A-Z a-z Remaining letters: A-Z a-z 0-9
May be as long as you want
Capitalization is important
May not include spaces

14. int declaration int numStudents;
Declares a variable to hold an integer number
Start variable names with a small letter
This variable will be named numStudents
It will set aside 1 32bit word of space
It can hold values between
-2,147,483,648 and +2,147,483,647

15. A Shortcut
When we create a variable we can also set it to a particular value
This is called “initialization”
Example:
int maxStudents = 30;

16. Integer Operators + Addition - Subtraction * Multiplication / Division
% Remainder

17. Division and Remainder
What is 5 / 9 ?
What is 5 % 9 ? 5
What is 28 / 9 ? 3
What is 28 % 9 ? 1

18. Integer Expressions
Use the integer operators on int variables and literals
Operators are applied left to right
Multiplication, Division, and Remainder are done before addition and subtraction
What is * 30 ?
307

19. Integer Expression (cont)
To control the order things happen use parens “(“ and “)”
What is (7 + 10) * 30 ?
510
Notice that parens do not imply multiplication
What is (7 + 10) 30 ?

20. With Variables How many seats are left in a class?
maxStudents - curEnroll
Where does the result go?
How do we save the result?
How do we use the result?

21. =
Equal Sign?
NO!

22. Assignment Operator = maxStudents = 30; Left side must be a variable
The value from the right is put in the spot in memory named on the left
. . . 30
maxStudents

23. maxStudents – curEnroll
Example
seatsLeft =
maxStudents – curEnroll ;
. . . 33
curEnroll
. . . -3 -3
seatsLeft
. . . 30
maxStudents

24. Example How to increase a number by 1 count = count + 1;
This is a very common case, be sure you understand it.
This is mathematical nonsense.

25. More Data Types
long
double
boolean

26. long What if I need a number that is too big to fit into an int?
long population;
Use pretty much like an int
long popNorthAmerica, popSouthAmerica, popNewWorld;
. . .
popNewWorld = popNorthAmerica + popSouthAmerica;

27. Caution An int will fit into a long
But, a long will not fit into an int
long myLong;
int myInt;
. . .
myLong = myInt + 17; // this is ok
myInt = myLong + 1; // this will not work

28. What if I need a fraction?
float and double give you numbers that have places to the right of the decimal point
float pi = 3.14;
Using float is a bad idea
double pi = 3.14;
Use double instead!

29. Arithmetic with doubles
double area;
double pi=3.14;
double radius=7.5;
…..
area = pi * (radius * radius);

30. Simple conversion No! No! No! int myInt=7; long myLong=77;
double myDouble=7.77;
No!
myInt = myLong;
myLong = myInt;
myInt = myDouble;
myLong = myDouble;
myDouble = myInt;
myDouble = myLong;
No!
No!

31. Note: true is not the same as “true”
boolean
A variable that can be true or false
boolean isVegetarian;
isVegetarian = true;
isVegetarian = false;
Note: true is not the same as “true”

32. Variable Declarations (Review)
Sets aside space in memory
Labels the space with a name
Declaration sets variable for a particular type – numbers, letters, etc.
Once type is set it can not be changed
Variable must be declared before it can be used

33. Comments
Comments are a way to stick notes to other people (and your self) in your program code
The compiler skips over comments
Therefore, no trace of your comments goes into the executable

34. Comments (cont) Two slashes comments out the rest of the line Example:
numStudents = 30; // current enrollment

35. Comments (cont)
A slash asterisk comments out every line until an asterisk slash is found
Example: /*
Current enrollment */
numStudents = 30;

36. Comments (cont) What if we do this: /* Current enrollment
numStudents = 30; */

37. Comments (cont) Use comments to put your name on your programs
Use comments to identify what your program does