Data Types

& Arithmetic Operations

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Week 2

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1

Helping Hand for Relief & Development

Goal of this lesson

• In this lesson, we will learn:
• About the primitive data types in Java
• How to make our own variables in Java
• How to assign and change data in our variables
• How to write print statements with variables
• How to perform simple arithmetic operations like addition, subtraction, multiplication, and division in Java

2

Key Terms

• Data type
• Primitive type
• Variable
• String
• int
• double
• boolean

3

We will learn about these terms in the next slides

What is a data type?

• A data type tells your computer what kind of information you want to store
• Numbers - 1, 2.0, 5, 1034
• Letters/Characters - A, b, Z, #, @
• Words - hello, goodbye, ayesha
• Sentences - nice to meet you!

4

Primitive

Non-primitive

Data types

Numbers

Letters

Characters

Words

Sentences

Quick Review

• Before we get into data types in Java, let us quickly review:
• Integer - whole numbers without decimals like 1, 2, 3, -1, -2, -3
• Examples: 5, 3029, 490
• Real Number - any non imaginary number (includes decimals)
• Examples: 320.43, π, e
• Binary - a base two number. In computer science it is either a 0 or 1

5

Data Types

• In Java, there are 8 primitive data types that allow us to store:
• Integers like 3, 5, 18 - byte, short, int, long
• Decimals like 4.2, 15.3 - float, double
• True or false - boolean
• Characters like ‘A’, ‘k’, ‘#’, ‘?’ - char
• There are also many non-primitive data types. Today we will only look at String that lets us store words and sentences

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Why we need data types

awesome + cool

1 + 2

Example

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• Here, we define the variable sum as the integer 0

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What is a variable?

• In order to create data types that store either numbers, characters, or strings, we need to have a name for the data.
• Variable: A piece of information that has a name, data type, and value

8

“Daanish”

name

0

sum

Most Important Data Types

• char - a character from a to z
• char letter = ‘m’;
• This sets the variable letter to the value m

• String - any arrangement of characters
• String test = “hello”;
• This sets the variable test to the value of hello

• boolean - 1 or 0/True or False
• boolean isOn = false;
• The variable isOn is set to false

9

Most Important Data Types

• byte - an integer between -2⁷ and 2⁷-1 (1 byte)
• byte num = 5;
• short- an integer between -2¹⁵ and 2¹⁵-1 (2 bytes)
• short num = 4398;

• int- an integer between -2³¹ and 2³¹-1 (4 bytes)
• int num = 54892;
• long - an integer between -2⁶³ and 2⁶³-1 (8 bytes)
• long num = 298483;

10

Most Important Data Types

• float - any number from -2³¹ and 2³¹-1 (4 bytes)
• float num = 2090.453
• double - any number from -2⁶³ and 2⁶³-1 (8 bytes)
• double num = 320958434.65

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Why It’s Important

• Important things to note:
• String and char use letters
• boolean helps with simple binary variables
• float and double use real numbers
• byte, short, int, and long deal with integers

12

Variable Declaration

• Variable declaration
• [data type] [variable name] = [value];
• The computer will put aside memory for the variable so it can reference the variable later in the program
• Example:
• int age = 17;
• String name = “Daanish”;
• Create two variables: one that stores your age and one for your name

13

Printing Variables

• Assuming I declared my variable greeting to be “hello”, I can print out the variable
• System.out.print(greeting); or System.out.println(greeting);
• The ln will put the phrase on a new line in the console
• To combine text and a variable, use the following syntax:
• System.out.print(“The variable greeting: ” + greeting);
• The console should read out “The variable greeting: hello”
• Try printing some things on your own!

14

Constant Declaration

• Constant declaration
• final [data type] [variable name] = [value];
• Including the word final lets the computer know the variable will never change in the program
• Example:
• final byte num = 2;
• final char char1= ‘d’;
• In what cases would you use a constant or a variable declaration?

15

Casting

• Widening Casting
• Converting a small type to a bigger type, such as a byte to a double
• int intNum = 5;�double doubleNum = intNum; //doubleNum is 5.0
• Narrowing Casting
• Converting a large type to a smaller type
• double doubleNum = 5.2;�int intNum = (int) doubleNum; //intNum is 5

16

CW Exercise 1

• Explain the difference between 2, 2.0, “2”, and “2.0”
• Cast an integer to a double, and a double to an integer. What happens?
• Create a program that says “hello my name is [insert name] I am [insert age] years old and I want to study [insert field] when I get older”
• Try doing this using variables, not just typing the phrase out into the System.out.print();

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Arithmetic Operations

• The 5 basic operations:
• Addition (+)
• Subtraction (-)
• Multiplication (*)
• Division (/)
• Modulo (%)

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Full Order of Operations

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Short Order of Operations

(1) () (parentheses)

(2) *, /, % (multiplication, division, modulo)

(3) +, - (addition, subtraction)

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Order of Operations - Key Points

• Key things to point out:
• Anything in parentheses is calculated first
• 2 * (3 + 4) = 14
• Multiplication, division, and remainder are one one level above addition and subtraction
• 2 * 3 + 4 = 10, and 2 + 3 * 4 = 14
• You can always go back to the previous slide if necessary when coding in the future

21

CW Exercise 2

• Using the following:

• Output the following in the console

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CW Exercise 3

• What will the following code produce? Make predictions for all the values

23

Use a calculator if necessary

Key Terms

• Data type
• Primitive type
• Variable
• String
• int
• double
• boolean

24

Define these terms in your own words, we will go over them in a minute

Key Terms

• Data type - Tells the computer what kind of info you want to store
• Primitive type - Simple data type (like integer, double, boolean)
• Variable - A piece of memory that has a data type and a value
• String - A data type that is a sequence of characters
• int - An integer data type that stores integers (ie. -3, -2, -1, 0, 1, 2..)
• double - A data type that stores real numbers (ie. -3.2, 4.5, 110)
• boolean - A data type that is either true or false

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What We Learned

• In this lesson, we learned:
• How to create our own variables in Java
• How to print different kinds of output
• About the primitive data types in Java
• How to perform addition, subtraction, multiplication, and division in Java

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Homework

• Here is the link to the homework.
• Please email your java file by Thursday, Feb 4th to hhrd.compsci@gmail.com

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Extra Reading

• Data types
• 2.2 - Data Types
• 2.3 - Variables
• 2.4 - Constants
• 2.5 - Converting Data types
• 2.6 - Mathematical Calculations
• 2.7 - java.lang.Math
• 2.8 - Comparison and Logical operators

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Questions?

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Feel free to ask!

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