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

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

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, 926394 double: 3.1, -0.25, 19.83425 char: 'a', 'X', '?', '\n' boolean: true, false Special (Object) Type: String: "Tuesday", "Java", "Hello World!"

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

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

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 " + 2017 "Interstate " + 9 + 5 20 + 20 + "Class"

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 / 2 + 7 / 3 = " + 6 / 2 + 7 / 3); System.out.println("6 * 7 % 4 = " + 6 * 7 % 4 ); System.out.println("22 + 4 * 2 = " + 22 + 4 * 2); }  Wrong answer! Fix this using () : Higher the evaluation precedence

Evaluation Precedence Precedence: Order in which operators are evaluated. Generally operators evaluate left-to-right. 1 - 2 - 3 is (1 - 2) - 3 which is -4 But * / % have a higher level of precedence than + - 1 + 3 * 4 is 13 6 + 8 / 2 * 3 6 + 4 * 3 6 + 12 is 18 Parentheses can force a certain order of evaluation: (1 + 3) * 4 is 16

Precedence Examples 1 * 2 + 3 * 5 % 4 \_/ | 2 + 3 * 5 % 4 \_/ | 2 + 3 * 5 % 4 \_/ | 2 + 15 % 4 \___/ | 2 + 3 \________/ | 5 1 + 8 % 3 * 2 - 9 \_/ | 1 + 2 * 2 - 9 \___/ | 1 + 4 - 9 \______/ | 5 - 9 \_________/ | -4

Homework I What values result from the following expressions? 9 / 5 695 % 20 7 + 6 * 5 7 * 6 + 5 248 % 100 / 5 6 * 3 - 9 / 4 (5 - 7) * 4 6 + (18 % (17 - 12))

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 " + 2017); System.out.println("Interstate " + 9 + 5); System.out.println(20 + 20 + " Class"); System.out.println("Class " + 20 + 20); }

Homework II What String result from the following expressions? "hello" + 42 is ______________ 1 + "abc" + 2 is ______________ "abc" + 1 + 2 is ______________ 1 + 2 + "abc" is ______________ "abc" + 9 * 3 is ______________ "1" + 1 is ______________ 4 - 1 + "abc" is ______________

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: 15.0 / 2.0 is 7.5 Precedence is the same: () before * / % before + -

Real Number Examples 2.0 * 2.4 + 2.25 * 4.0 / 2.0 \___/ | 4.8 + 2.25 * 4.0 / 2.0 \___/ | 4.8 + 9.0 / 2.0 \_____/ | 4.8 + 4.5 \____________/ | 9.3

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)

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;

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

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

Printing a Variable’s Value Using '+', attach a variable’s value to the existing String object double grade = (95.1 + 71.9 + 82.6) / 3.0; System.out.println("Your grade was " + grade); int students = 11 + 17 + 4 + 19 + 14; System.out.println("There are " + students + " students in the course.");

Program III: Receipt public class Receipt { public static void main(String[] args) { // Calculate total owed, assuming 6% tax / 15% tip int subtotal = 38 + 40 + 30; 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); }