1. Variables & Data Types
Java

2. Variables
Variables – a cup … a container…. It holds something… some type of data
When we declare a variable in Java, we must tell our program what type of data will be stored in that variable
It’s no longer OK to just say the variable is a ‘number’ – we must specify WHAT kind of number
Always be aware of the type of data your program is processing
Variables can change values throughout a program

3. Primitive Data Types
Data types – what KIND of data is stored in the variable
There are 8 primitive data types (built-in types), but we mostly use:
Int – integers (whole numbers… no decimal points)
Double – numbers that contain decimal points. Called floating-point numbers
Boolean – true or false
String – sequence of characters

4. Integers Int x = 7; This line is considered a declaration
It declares the name of a variable (x) – also called an identifier
It declares the data type of x – it’s an int
The equal assign is an assignment operator
Java is a strongly-type language – must declare data type

5. Integers Can hold values between -2147483648 and 2147483648
You can use standard arithmetic operations for addition (+), subtraction (-), multiplication (*), division (/), and the remainder of division (%)

6. Addition/Subtraction
Public class AddNumbers { public static void main (String[] args) int x = 7; int y = 6; int z = x +y; System.out.println(z); }

7. Division Public class DivideNumbers {
public static void main (String[] args)
int weeklyPay = 800;
int hoursWorked = 40;
int hourlyRate = weeklyPay/hoursWorked;
System.out.println(hourlyRate); }

8. Multiplication
int weeklyRate = 20; int hoursWorked = 40; int WeeklyPay = hourlyRate*hoursWorked; System.out.println(WeeklyPay);

9. Modulus (remainder
Int x = 7; Int y = 3; Int z = x % y; // z will be 1 System.out.println(z);

10. Floating Point Numbers
Numbers that contain decimal places
Double and Float
Precision – how accurate do you need your data to be? How many decimal places do you need?
Double is the generally used data type for decimal places

11. Double
Double hourlyRate = 15.75; Double hoursWorked = 38.25; Double totalPay = hourlyRate * hoursWorked; // will display //this won’t compile Int totalPay = hourlyRate * hoursWorked;

12. Double - continued // this won’t compile Double hourlyRate = 15.75;
Int hoursWorked = 38.25;
Double totalPay = hourlyRate * hoursWorked;
System.out.println (totalPay)
// this will compile
Int hoursWorked = 38;

13. Classroom Learning
Create a Java program named Pay that calculates a worker’s net pay after taxes.
Establish appropriate variables for:
A person’s hourly rate
The number of hours worked
The person’s tax rate
The gross pay
The amount of taxes taken off
The net pay

14. Payroll - continued Assign the following values to the variables:
The hourly rate should be 9.25 per hour
The number of hours worked should be 32
The person’s tax rate is 18%
The gross pay should calculate hourly rate * number of hours worked
Taxes should be gross pay * tax rate
Net pay should be gross pay – taxes
At the end of the program display “Your net pay is _________ Thank you!!”

15. Getting input from UserScanner Class
import java.util.Scanner; [at top of program] [after public static void …..] Scanner response = new Scanner(System.in); Int testVariable; [putting input from scanner into a variable] System.out.print (“what is 1st number?”); testVariable = response.nextInt()

16. Boolean Boolean isMale = true; Boolean isFemale = false;
Has just two values – true or false
Used with conditional/decision-making logic

17. Strings Sequence of characters Needs to be stored in quotes
String firstName = “Chet”;
Data type upper case “S”

18. Changing Variable Valeus
int x = 7; int y = 6; X = 5; int z = x +y; //z is 11 //will get compiler errors Int x = 7; Int y = 6; Int x = 5; Int z = x + y;

19. Concatenation Used to combine two strings or a number and a string
String firstName = “Chet”;
String lastName = “Brown”;
System.out.println (firstName + lastName);
//will display ChetBrown
System.out.println (firstName + “ “ + lastName);
// will display Chet Brown

20. Concatenation – cont’d
String firstName = “Chet”; Int age = 25; System.out.println(FirstName + “ is” + age + “years old”); //will display Chet is 25 years old