1. Week 4 - Friday
CS 121

2. Last time
What did we talk about last time?
Examples
switch statements

3. Questions?

4. Project 1

5. Review

6. Week 1 review topics History of computers Hardware
Software development
Basic Java syntax
Output with System.out.print()

7. History of computers Mechanical Calculation Devices (2400BC onward)
Aid to human calculation
No stored program
Mechanical Computers (1725 onward)
Punch card programming
Serious limitations
Early Electronic Computers (1941 onward)
General purpose, stored program computers
Electronic, using vacuum tubes
Microprocessors (1970's onward)
Succeeded transistors
Now billions of computations per second at a nanometer scale

8. Memory Cache RAM Flash Drive Hard Drive Optical Drive
Actually on the CPU
Fast and expensive
RAM
Primary memory for a desktop computer
Pretty fast and relatively expensive
Flash Drive
Faster than hard drives
Seen on USB drives but SSDs are becoming common too
Hard Drive
Secondary memory for a desktop computer
Slow and cheap
Optical Drive
Secondary memory that can usually only be written once
Very slow and very cheap

9. Memory Storage for all the data and instructions on your computer
Modern computers store everything as binary digits (bits) which have a value of 0 or 1.
1 byte
= 8 bits
1 kilobyte (kb)
= 210 bytes
1 megabyte (mb)
= 220 bytes
1 gigabyte (gb)
= 230 bytes
1 terabyte (tb)
= 240 bytes

10. Input/Output Monitor Speakers Mouse Keyboard
Common visual output device
Speakers
Common audio output device
Mouse
Common input device
Keyboard

11. General compilation model
Solve a problem;
Computer!
Source Code
Machine Code
Hardware

12. Compilation and Execution for Java}
p.solve();
Problem p; {
class A
Java
Source
Code
Java Bytecode
Machine Code
Hardware
Platform
Independent
Platform
Dependent

13. Software development
Often goes through phases similar to the following:
Understand the problem
Plan a solution to the problem
Implement the solution in a programming language
Test the solution
Maintain the solution and do bug fixes
Factor of 10 rule!

14. A basic Java program
The absolute smallest program possible, with a print statement
public class Hello {
public static void main(String[] args)
System.out.println("Hello, world!"); }

15. Sequencing
For example, instead of one print statement, we can have several:
Each statement is an instruction to the computer
They are printed in order, one by one
System.out.println("Hello, world!");
System.out.println("Hello, galaxy!");
System.out.println("Goodbye, world!");

16. Case Sensitivity Java is a case sensitive language
Class is not the same as class
System.out.println("Word!"); prints correctly
system.Out.Println("Word!"); does not compile

17. Whitespace
Java generally ignores whitespace (tabs, newlines, and spaces)
is the same as:
You should use whitespace effectively to make your code readable
System.out.println("Hello, world!");
System.out.
println( "Hello, world!");

18. Comments There are two kinds of comments (actually 3)
Single line comments use //
Multi-line comments start with a /* and end with a */
System.out.println("Hi!"); // this is a comment
System.out.println("Hi!"); /* this is
a multi-line
comment */

19. Week 2 review topics Binary representation Basic data types
Using Scanner for input

20. Base 2 (binary) numbers The binary number system is base 2
This means that its digits are: 0 and 1
Base 2 means that you need 2 digits to represent two, namely 1 and 0
Each place in the number as you move left corresponds to an increase by a factor of 2 instead of 10

21. 11111100001 Base 2 Example Sixty fours 256’s Sixteens Fours 1024’s
Ones
512’s
128’s
Thirty twos
Eights
Twos

22. Built-in types We're focusing on five basic types of data in Java
These are:
int For whole numbers
double For rational numbers
boolean For true or false values
char For single characters
String For words
String is a little different from the rest, since you can call methods on it (and for other reasons)

23. Summary of types Type Kind of values Sample Literals int double
Integers -5
900031
double
Floating-point
Numbers
3.14
-0.6
6.02e23
boolean
Boolean values
true
false
char
Single characters
'A'
'Z'
'&'
String
Sequences of
characters
"If you dis Dr. Dre"
"10 Sesquipedalians"

24. The int type
The int type is used to store integers (positive and negative whole numbers and zero)
Examples: 54
Inside the computer, an int takes up 4 bytes of space, which is 32 bits (1's and 0's)

25. The double type You will use the int type very often
Sometimes, however, you need to represent numbers with a fractional part
The double type is well suited to this purpose
Declaration of a double variable is just like an int variable:
double x;

26. The boolean type Numbers are great
But, sometimes you only need to keep track of whether or not something is true or false
This is what the boolean type is for
Hopefully you have more appreciation for booleans now
Declaration of a boolean variable is like so:
boolean value;

27. The char type Sometimes you need to deal with characters
This is what the char type is for
The char type only allows you to store a single character like '$' or 'q'
Declaration of a char variable is like so:
char c;

28. The String type
The String type is different from the other types in several ways
The important thing for you to focus on now is that it can hold a large number of chars, not just a single value
A String literal is what we used in the Hello, World program
String word;

29. Using Scanner There are three parts to using Scanner for input
Include the appropriate import statement so that your program knows what a Scanner object is
Create a specific Scanner object with a name you choose
Use the object you create to read in data

30. Importing Scanner
Lots of people have written all kinds of useful Java code
By importing that code, we can use it to help solve our problems
To import code, you type import and then the name of the package or class
To import Scanner, type the following at the top of your program (before the class!)
import java.util.Scanner;

31. Creating a Scanner object
Once you have imported the Scanner class, you have to create a Scanner object
To do so, declare a reference of type Scanner, and use the new keyword to create a new Scanner with System.in as a parameter like so:
You can call it whatever you want, I chose to call it in
Doesn't make any sense? For now, that's okay.
Scanner in = new Scanner(System.in);

32. Using a Scanner object
Now that you've got a Scanner object, you can use it to read some data
It has a method that will read in the next piece of data that user types in, but you have to know if that data is going to be an int, a double, or a String
Let's say the user is going to input her age (an int) and you want to store it in an int variable called years
We'll use the nextInt() method to do so:
int years;
years = in.nextInt();

33. Scanner methods
Scanner has a lot of methods (ways to accomplish some tasks)
For now, we're only interested in three
These allow us to read the next int, the next double, and the next String, respectively:
Scanner in = new Scanner(System.in);
int number = in.nextInt();
double radius = in.nextDouble();
String word = in.next();

34. Week 3 review topics Numerical operations Advanced math operations
boolean operations
char operations
String operations
Wrapper classes

35. Numerical operations + adds - subtracts * multiplies
/ divides (integer division for int type and fractional parts for double type)
% finds the remainder

36. Complex expressions Order of operations holds like in math
You can use parentheses to clarify or change the precedence
Now a is 16
int a = 31;
int b = 16;
int c = 1;
int d = 2;
a = (((b + c) * d) – a / b) / d;

37. Casting You cannot directly store a double value into an int variable
However, you can cast the double value to convert it into an int
Casting tells the compiler that you want the loss of precision to happen
You can always store an int into a double
int a = 2.6; // fails!
int a = (int)2.6; // succeeds! (a = 2)

38. Math method example with sin()
The sin() method allows you to find the sine of an angle (in radians)
This method is inside the Math class
The answer that it gives back is of type double
To use it, you might type the following:
double value = Math.sin( 2.4 );

39. Rounding
In Java, the conversion of a double into an int does not use rounding
As in the case of integer division, the fractional part is dropped
For positive numbers, that's like using floor
For negative numbers, that's like using ceiling
The right way to do rounding is to call Math.round()
double x = 2.6;
int a = (int)Math.round(x); // rounds

40. Math methods Return type Name Job double sin( double theta )
Find the sine of angle theta
cos( double theta )
Find the cosine of angle theta
tan( double theta )
Find the tangent of angle theta
exp( double a )
Raise e to the power of a (ea)
log( double a )
Find the natural log of a
pow( double a, double b )
Raise a to the power of b (ab)
long
round( double a )
Round a to the nearest integer
random()
Create a random number in [0, 1)
sqrt( double a )
Find the square root of a
toDegrees( double radians )
Convert radians to degrees
toRadians( double degrees )
Convert degrees to radians

41. boolean operations ! NOT && AND || OR ^ XOR
Flips value of operand from true to false or vice versa
&& AND
true if both operands are true
|| OR
true if either operand is true
^ XOR
true if operands are different

42. Short circuit evaluation
In some circumstances, Java doesn't check the whole expression:
(true || (some complicated expression))
Ignores everything after || and gives back true
(false && (some complicated expression))
Ignores everything after && and gives back false

43. char operations char values can be treated like an int
It can be more useful to get the offset from a starting point
int number;
number = 'a'; // number contains 97
char letter = 'r';
int number;
number = letter – 'a' + 1;
//number is 18

44. Escape sequences
Remember that we use single quotes to designate a char literal: 'z'
What if you want to use the apostrophe character ( ' )?
apostrophe: '\''
What if you want to use characters that can't be printed, like tab or newline?
tab: '\t'
newline: '\n'
The backslash is a message that a special command called an escape sequence is coming
These can be used in String literals as well:
"\t\t\t\nThey said, \"Wow!\""

45. String concatenation
The only operator that we will use directly with Strings is the + (concatenation) operator
This operator creates a new String that is the concatenation of the two source Strings
Concatenation can be used to insert the values of other types into Strings as well
String word;
word = "tick" + "tock"; // word is "ticktock"

46. String methods equals() compareTo() length() charAt() substring()
Tests two Strings to see if they are the same
compareTo()
Returns a negative number if the first String comes earlier in the alphabet, a positive number if the first String comes later in the alphabet, and 0 if they are the same
length()
Returns the length of the String
charAt()
Returns the character at a particular index inside the String
substring()
Returns a new String made up of the characters that start at the first index and go up to but do not include the second index

47. Wrapper classes Each primitive data type in Java has a wrapper class
Integer
Allows String representations of integer values to be converted into ints
Double
Allows String representations of floating point values to be converted into doubles
Character
Provides methods to test if a char value is a digit, is a letter, is lower case, is upper case
Provides methods to change a char value to upper case or lower case

48. Week 4 review topics Making choices with if statements
Basics
Having if bodies with more than one line
Using else blocks
Nesting if statements
Using switch statements

49. if( condition ) statement; Anatomy of an if Any boolean expression
The if part
if( condition )
statement;
Any single executable statement

50. Two different outcomes
Anatomy of an if-else
if( condition )
statement1;
else
statement2;
Two different outcomes

51. An if with multiple statements
if( condition ) {
statement1;
statement2; …
statementn; }
A whole bunch of statements

52. Nested ifs if( condition1 ) { statement1; if( condition2 )… }

53. Comparison
The most common condition you will find in an if is a comparison between two primitive types
In Java, that comparison can be:
== equals
!= does not equal
< less than
<= less than or equal to
> greater than
>= greater than or equal to

54. Anatomy of a switch statement
switch( data ) {
case value1:
statements 1;
case value2:
statements 2; …
case valuen:
statements n;
default:
default statements; }

55. Peculiarities of switch
Both "Three" and "Four" are printed
int data = 3;
switch( data ) {
case 3: System.out.println("Three");
case 4:
System.out.println("Four");
break;
case 5:
System.out.println("Five"); }
Go to SwitchAge
The break is optional
The default is optional too

56. Rules for switch
The data that you are performing your switch on must be either an int, a char, or a String
The value for each case must be a literal
Execution will jump to the case that matches
If no case matches, it will go to default
If there is no default, it will skip the whole switch block
Execution will continue until it hits a break

57. Lab 4

58. Upcoming

59. Next time…
Exam 1

60. Reminders Study for Exam 1
Keep working on Project 1, due tonight by 11:59!
Never look at another student's code