1. What You Should Already Know
Review of CSCI 1226
What You Should Already Know

2. What You Should Already Know
Basic programming
program class: class declaration, main method
output: System.out, print & println
variables: declaration, assignment, arithmetic
data types: int, double, boolean, String
input using Scanners:
import, declare, and create
nextInt, nextDouble, next, nextLine
“tidying up” your input

3. What You Should Already Know
Comments
why and when we use them
to end-of-line: // …
multi-line: /* … */
javadoc: /** … */
Style
names and why they’re important
camelCase, CONSTANT_STYLE
indentation, spacing, line length

4. What You Should Already Know
Conditionals and boolean expressions
maybe do: the if control
comparisons: ==, !=, <, <=, >, >=
logical operators: !, &&, ||
exactly one of two: if-else
exactly (or at most) one of many: if-else-if
String methods that return boolean values
equals, equalsIgnoreCase, startsWith, …

5. What You Should Already Know
Loops
definite loops: the for loop (count controlled)
indefinite loops: the while loop
sentinel control: Read-Test-Process-Read
general control: Initialize-Test-Process-Update
Arrays
declare, create, get length of
standard loop for visiting every element

6. What You Should Already Know
Methods (using)
parts of the method call
location/owner, method name, arguments
return value (including void)
Math methods: pow, sqrt, random, …
Arrays methods: toString, sort
String methods: toUpper, toLower, length, …

7. What You Should Already Know
Methods (creating)
why we create methods
reuse, hiding, abstraction
the method’s task/purpose/job
creating a class of related static methods
parts of the method declaration
public/private static, return type, name, parameters
body (including return command)
what a stub is and why we make them

8. What You Should Already Know
Data Types (using)
class data types: String, Scanner, …
variables, objects, and reference:
String myName = “Mark”;
Scanner kbd = new Scanner(System.in);
asking objects questions
getting information about them: getters
changing their information: setters
getting them to do things

9. What You Should Already Know
Data Types (creating)
why we create data types: representation
creating a class for a data type
parts of the data type
instance variables (private) and constants (final)
constructors: assigning values, this(…)
creating getter and setter methods: this.___
static variables, constants, and methods
why, when, and how

10. Review Outline Today: Next week: Following week:
conditionals, loops, and arrays
Next week:
arrays and methods, multi-dimensional arrays
Following week:
data types and the Javabean pattern

11. Purpose of a Conditional
Maybe do some command
need to know the conditions for doing it
if the user says they want fries add fries to the order
Choose between multiple actions
set the letter grade based on the percent grade:
80 or more: A; 70 to 79: B, 60 to 69: C, 50 to 59: D; otherwise F

12. Do or Do Not(*) if user says “yes” to the question say “FRIES!”
What sandwich? Big Greesie
BIG GREESIE!
Would you like fries with that? yes
FRIES!
What can I get you to drink? Cola
COLA!
That'll be $11.93.
What sandwich? Big Greesie
BIG GREESIE!
Would you like fries with that? no
What can I get you to drink? Cola
COLA!
That'll be $9.94.
Maybe add fries…
Total depends…
Total depends…
if user says “yes” to the question
say “FRIES!”
add the price of the fries to the total
(*) There is no try in CSCI 1226…

13. Do or Do Not System.out.print(“What sandwich? ”);
answer = kbd.nextLine();
System.out.println(answer.toUppercase() + “!”);
total += 8.95;
System.out.print(“Want fries with that? ”);
if (answer.startsWith(“y”)) { System.out.println(“FRIES!”);
total += 1.99; } …
if they say they want fries…
…add fries to the order

14. Cascading If Statements
Else part can have an if command in it
if (…) {
…; // program might do this…
} else if (…) {
…; // …or this…
} else {
…; // …or this. }
program chooses one of those four things to do

15. Using Conditionals
Conditionals are used when you need to do only one of multiple possible actions
remembering that “do nothing” may be one of the possible actions
Look for “Do one of the following” or “if such-and-such, do …”

16. Building a Selection Structure
Enumerate the alternatives
what are the possible actions?
is do nothing one of the alternatives?
print “It’s hot!”
print “It’s warm.”
print “It’s cool.”
print “It’s cold!”
print “It’s nice.”

17. Building a Selection Structure
Identify the conditions
when is each action the right thing to do?
30 <= temp
print “It’s hot!”
25 <= temp < 30
print “It’s warm.”
5 <= temp < 15
print “It’s cool.”
temp < 5
print “It’s cold!”
15 <= temp < 25
print “It’s nice.”

18. Building a Selection Structure
Sort the options
from “largest” to “smallest”…
…or from “smallest” to “largest”
30 <= temp
print “It’s hot!”
25 <= temp < 30
print “It’s warm.”
15 <= temp < 25
print “It’s nice.”
5 <= temp < 15
print “It’s cool.”
temp < 5
print “It’s cold!”

19. Building a Selection Structure
Assign if/else-if/else
first is if; last is else; others are else if if
30 <= temp
print “It’s hot!”
else if
25 <= temp < 30
print “It’s warm.”
else if
15 <= temp < 25
print “It’s nice.”
else if
5 <= temp < 15
print “It’s cool.”
else
temp < 5
print “It’s cold!”

20. Building a Selection Structure
Simplify the conditions
drop the part that’s implied
We won’t get here
unless temp < 30 if
30 <= temp
print “It’s hot!”
else if
25 <= temp
print “It’s warm.”
else if
15 <= temp
print “It’s nice.”
else if
5 <= temp
print “It’s cool.”
Nor here unless
temp < 5
else
print “It’s cold!”

21. Building a Selection Structure
Add parentheses, indentation, braces, …
if (30 <= temp) {
System.out.print(“It’s hot!”);
} else if (25 <= temp) {
System.out.print(“It’s warm.” );
} else if (15 <= temp) {
System.out.print(“It’s nice.” );
} else if (5 <= temp) {
System.out.print(“It’s cool.” );
} else {
System.out.print(“It’s cold!” ); }

22. Building a Selection Structure
If there is a do nothing option, leave it out
if (30 <= temp) {
System.out.print(“It’s hot!”);
} else if (temp < 5) {
System.out.print(“It’s cold!”); }
30 <= temp
print “It’s hot!”
But be careful with the conditions!
5 <= temp < 30
(do nothing)
temp < 5
print “It’s cold!” {
} else if (5 <= temp) {

23. Boolean Expressions Comparison operators:
==, !=, <, <=, >, >=
equals, not equals, less, less or equal, …
(hours <= 40)
Logical operators combine conditions
and, or, not  &&, ||, !
parentheses recommended (needed for !)
((40 < hours) && (hours <= 60))

24. Combined Comparisons Cannot combine comparisons like this:
if (40 < hours <= 60) …
Need to break into two parts:
if ((40 < hours) && (hours <= 60))

25. Combined Comparisons Cannot combine comparisons like this:
if (hours > 40 && <= 60) …
Need to say what’s less-than-or-equal-to 60
explicitly
if ((hours > 40) && (hours <= 60))

26. Exercise Write a conditional to set letterGrade based on numericGrade:
numericGrade in  letterGrade is ‘A’
numericGrade in  letterGrade is ‘B’
numericGrade in  letterGrade is ‘C’
numericGrade in  letterGrade is ‘D’
numericGrade less than 50  letterGrade is ‘F’
(assume numericGrade is )

27. Purpose of a Loop Do something multiple times
write “Hello” ten times
for count goes from 1 to 10 write “Hello”
Do same thing to many objects/values
add each number to a running total
for each number in the list add that number to the running sum

28. How Many Times?
Do we know how many times the loop body will execute before we start the loop?
if so, we want to use a for loop
if not, then we want to use a while loop
Enter six assignment grades: for loop
for (int a = 1; a <= 6; ++a) { … }
Add up numbers until negative: while loop
while (num >= 0) { … }

29. Before, During, and After
Notice part that repeats, and parts that don’t
Enter all your grades.
Grade on A1: 100
Grade on A2: 90
Grade on A3: 95
Grade on A4: 0
Grade on A5: 100
Grade on A6: 95
Your average is 80.0
Before repeats
Repeats (6 times)
One iteration
After repeats

30. Before, During & After System.out.println(“Enter all your grades.”);
Before repeats
System.out.println(“Enter all your grades.”);
int numAsgn = 6;
double sum = 0.0;
for (int a = 1; a <= numAsgn; a++) { System.out.print(“Grade on A-” + a + “: ”);
double grade = kbd.nextDouble();
kbd.nextLine(); sum += grade; }
double ave = sum / numAsgn;
System.out.println(“Your average is ” + ave);
Repeats
(6 times)
One iteration
After repeats

31. Before, During, and After
Notice part that repeats, and parts that don’t
Enter -1 to end.
Enter first number: 100
Enter next number: 90
Enter next number: 95
Enter next number: 42
Enter next number: -1
The total is 327
Before repeats
Repeats (until -1 entered)
One iteration
After repeats

32. Before, During & After int sum = 0.0;
Before repeats
int sum = 0.0;
System.out.println(“Enter -1 to end.”);
System.out.print(“Enter first number: ”);
int num = kbd.nextInt(); kbd.nextLine();
while (num >= 0){ sum += num;
System.out.print(“Enter next number: ”);
num = kbd.nextInt();
kbd.nextLine(); }
System.out.println(“The total is ” + sum);
Repeats
(until -1
entered)
One iteration
After repeats

33. “Sentinel” Loops Goes until a special value is entered
any number less than 0 for the last loop
even tho’ it asked specifically for -1
Usually need to get 1st value before the loop
then use the value (top of loop body)
get the next value last (bottom of loop body)
READ
TEST
PROCESS

34. “Sentinel” Loop int sum = 0.0; System.out.println(“Enter -1 to end.”);
System.out.print(“Enter first number: ”);
int num = kbd.nextInt(); kbd.nextLine();
while (num >= 0){ sum += num;
System.out.print(“Enter next number: ”);
num = kbd.nextInt();
kbd.nextLine(); }
System.out.println(“The total is ” + sum);
Read
Test
Process
Read

35. Exercise
Write a loop to read in names, stopping when no name is entered. Say how many names there were.
Who is in your class?
Name (leave blank to end): Alex
Name (leave blank to end): Bernard
Name (leave blank to end): Cathy
Name (leave blank to end):
There are 3 students in your class.
Remember: READ, test, process, read

36. Arrays Array type is just another data type
int anIntVar; // anIntVar’s type is int
int[] aBunchOfIntVars; // aBunchOfIntVars’ type is int[]
Create by adding [] to a data type
any data type!
double[] aBunchOfDoubleVars;
String[] aBunchOfStringVars;
Scanner[] aBunchOfScannerVars;
int[][] aBunchOfIntArrayVars;

37. Arrays Arrays need to be created with “new” like Scanners
double[] someNumbers = new double[20];
String[] someWords = new String[1000];
word after “new” matches the base data type
base data type = what kind of values are in the array
put the size of the array in the [brackets]
the size can be a variable, but it must have a value
int howManyLines = kbd.nextInt(); kbd.nextLine();
String[] theLines = new String[howManyLines];

38. Arrays An array is a collection/list of variables
each element is of the base type
int, double, String, …
Individual variables picked out using []
someNumbers[3]
brackets go right after the name of the array
number inside the brackets called the index
indexes (or indices) start at 0 (NOT 1!)

39. Array Loops Array elements can be used individually…
a[0] = a[1] + a[2] * a[3];
…but usually used as a group/list
do same thing to each element of the array
for (int i = 0; i < someNumbers.length; ++i) {
someNumbers[i] = Math.sqrt(i); }
usually in a for loop
usually from 0 to less than the length of the array

40. Array Loop Upper Bounds
Every array knows how long it is
use its “dot-length property”
someNumbers.length, someWords.length, …
Or if you have a variable for its length…
double[] grades = new double[numStu];
for (int i = 0; i < numStu; ++i) { … }
Do not use a “magic number”
double[] grades = new double[100];
for (int i = 0; i < 100; ++i) { … }
It’s error-prone
(tends to add bugs to your program)

41. Use Arrays… To remember lots of values
read & print 3 numbers in reverse is easy
int a1, a2, a3;
a1 = kbd.nextInt(); a2 = kbd.nextInt(); a3 = kbd.nextInt();
System.out.println(a3 + “ ” + a2 + “ ” + a1);
but read and print 300 numbers in reverse?!?!
int[] a = new int[300];
for (int i = 0; i < a.length; i++) { a[i] = kbd.nextInt(); }
for (int i = a.length – 1; i >= 0; i--) { Sop(a[i] + “ ”); }
well that was pretty easy, too!

42. Remember Values for Later Use
// read and sum the numbers double[] temps = new double[7]; double sum = 0.0; S.o.p(“Enter ” + temps.length + “ daily highs.”); for (int i = 0; i < NUM_ITEMS; i++) { temps[i] = kbd.nextDouble(); // read the # sum += num[i]; // add it to sum } kbd.nextLine(); // tidy up input stream // calculate the average double ave = sum / temps.length; // print the difference from the average of each for (int i = 0; i < temps.length; i++) { S.o.p((num[i] – ave));
WeeklyTemps.java

43. Exercise
Create a program fragment to read in six grades, then print them in a table and show the average:
labels and grades separated by tabs
lines end after the labels/numbers are printed
so where does the System.out.println() go?
A A A A A A6
Your average: 75.0

44. To Be Continued…
Next two weeks:
Methods
Objects