1. Lecture 2: Data Types, Variables, Operators, and Expressions
Dr. Kyung Eun Park
Summer 2017

2. Data Types as Data Categories
Data Categorization:
Integer
Real number
Character
String
Boolean
Data Types: Determine the operators’ behavior
/ (division) for integer numbers or for real numbers

3. Primitive Data Types Primitive Types:
Java supports 8 simple types for numbers, text, etc.:
byte, short, int, long, float, double, char, & boolean
Commonly Used Primitive Types in Java
int: 42, -3, 0,
double: 3.1, ,
char: 'a', 'X', '?', '\n'
boolean: true, false
Special (Object) Type:
String: "Tuesday", "Java",
"Hello World!"

4. Numeric Operators Numeric Binary Operators: Numeric Unary Operator:
Combines two values (operands: left and right)
3*4, 9/2, 68%4, etc.
+ addition
- subtraction (or negation)
* multiplication
/ division
% modulus (a.k.a. remainder)
Numeric Unary Operator:
-5, +6

5. Keywords (Reserved Words)
keyword: An identifier that you cannot use because it already has a reserved meaning in Java.
abstract default if private this
boolean do implements protected throw
break double import public throws
byte else instanceof return transient
case extends int short try
catch final interface static void
char finally long strictfp volatile
class float native super while
const for new switch
continue goto package synchronized

6. Expressions Simple Expression:
Numeric expressions:
1+1, 3*4, (1+5)*50, 10/3, 9%3
String expressions:
"Hello World!"
Numeric expression plus ('+') String value
String concatenation
(2*6)+(4*4)+10
"Hello " + "World!"
"Summer "
"Interstate "
"Class"

7. Program I: Numeric Data Types
public class DataTypes { public static void main(String[] args) { System.out.println("5*8/6 = " + 5*8/6); System.out.println("(2*6)+(4*4)+10 = " + (2*6)+(4*4)+10); System.out.println("6 / / 3 = " + 6 / / 3); System.out.println("6 * 7 % 4 = " + 6 * 7 % 4 ); System.out.println(" * 2 = " * 2); }  Wrong answer! Fix this using () : Higher the evaluation precedence

8. Evaluation Precedence
Precedence: Order in which operators are evaluated.
Generally operators evaluate left-to-right is (1 - 2) - 3 which is -4
But * / % have a higher level of precedence than * 4 is 13
6 + 8 / 2 * 3
* 3
is 18
Parentheses can force a certain order of evaluation: (1 + 3) * 4 is 16

9. Precedence Examples 1 * 2 + 3 * 5 % 4 \_/ | 2 + 3 * 5 % 4
\_/ | * 5 % 4
\_/ | % 4
\___/ |
\________/ |
1 + 8 % 3 * 2 - 9
\_/ | * 2 - 9
\___/ |
\______/ |
\_________/ |

10. Homework I What values result from the following expressions? 9 / 5
695 % 20
7 + 6 * 5
7 * 6 + 5
248 % 100 / 5
6 * / 4
(5 - 7) * 4
6 + (18 % ( ))

11. Program II: Evaluation
public class Evaluation { public static void main(String[] args) { System.out.println("Hello, world!"); System.out.println("Hello " + "World!"); System.out.println("Summer " ); System.out.println("Interstate " ); System.out.println( " Class"); System.out.println("Class " ); }

12. Homework II What String result from the following expressions?
"hello" + 42 is ______________
1 + "abc" + 2 is ______________
"abc" is ______________
"abc" is ______________
"abc" + 9 * 3 is ______________
"1" + 1 is ______________
"abc" is ______________

13. Real Number Examples: 6.022 , -42.0 , 2.143e17
Placing .0 or . after an integer makes it a double
The operators + - * / % () all still work with double.
/ produces an exact answer: / 2.0 is 7.5
Precedence is the same: () before * / % before + -

14. Real Number Examples 2.0 * 2.4 + 2.25 * 4.0 / 2.0
\___/ | * 4.0 / 2.0
\___/ | / 2.0
\_____/ |
\____________/ |

15. Where to store values?
A Named Container for Rewritable Values: variable!!!
Variables are used to hold different types of values:
Integer number: int container (variable)
Real number: double or real container (variable)
Character symbol: char container (variable)
Boolean logical value: boolean container (variable)
String text: String container (object)

16. Variable Declaration Variable declaration: Syntax
Sets aside memory for storing a value
Variables must be declared before they can be used
Syntax
type name;
The name is an identifier.
An identifier name must start with a letter or _ (underscore) or $
Construct using letters [A-Za-z], digits [0-9], and ‘_’ and ‘$’ symbols
int x;
double taxRate;

17. Assignment Assignment: Stores a value into a variable. Syntax
name = expression;
int x; x = 3;
x = x + 3;
double taxRate; taxRate = 0.06; x 3 x 6
taxRate
0.06

18. Declaration/initialization
A variable can be declared/initialized in one statement.
Syntax
type name = expression;
int x = 3;
double taxRate = 0.06;

19. Printing a Variable’s Value
Using '+', attach a variable’s value to the existing String object
double grade = ( ) / 3.0;
System.out.println("Your grade was " + grade);
int students = ;
System.out.println("There are " + students +
" students in the course.");

20. Program III: Receipt
public class Receipt { public static void main(String[] args) { // Calculate total owed, assuming 6% tax / 15% tip int subtotal = ; double tax = subtotal * .06; double tip = subtotal * .15; double total = subtotal + tax + tip; System.out.println("Subtotal: " + subtotal); System.out.println("Tax: " + tax); System.out.println("Tip: " + tip); System.out.println("Total: " + total); }