DataTypes and Variables

Memory (Unit) - Bit, Byte
programming space doesn't used.

int price = 35000;
String brand = "hp";

Leftside
(int, tring) --> Datatype
(price, brand) --> Identifiers/ Reference Variable
= -->Assign or Assignment operator
Rightside
(35000, "hp") --> Value
; --> End of statement

C,C++, Java --> Statically Typed Programming Language
Python, JavaScript --> Dynamically Typed Programming Language

Variables

Variable Declaration Syntax (Single Variable)

data_type variableName = value;
(ex: int number =10;)

Multiple variables of the same data type

data_type variableName1 = value1, variableName2 = value2;
(ex: String firstName="Arunkumar", lastName = "Selvam";)

Syntax of Variable Declaration & Initialization

data_type variableName; (Variable Declaration)

data_type variaableName = value; (Variable Initialization)

Example:

String userName; // Variable Declaration
String userName = "Arunkumar"; //Variable Initialization

Points to Remember While Using Variables:

In Java, always initialize variables before using them with a default value.
Variables can only be accessed within their code block or scope. Don't try to use them outside of scope.
The variable type and the value assigned must match.
Give variables meaningful names.
Use the final keyword for values that shouldn't change during the program. These are called constants.

Variable Naming Convention

Variable names are case-sensitive.
In Java, variable names should follow camelCase (e.g., firstName, lastName).
They should not start with special characters like & (ampersand), $ (dollar), or _ (underscore).
Avoid using single-character variables like x, y, or z.

Types of Variables

Local
Global (Field)
- Static
- Non-Static

Data Types in Java

Byte
Short
Int (Integer)
Long
Float
Double
Boolean
Char
String

Note

These are reserved keywords in java.

1 Byte = 8 Bit

1 bit - binary
digit - 0,1s

base2 - 0,1 (Computer Usage)
base8 - 01234567
base10 - 0123456789 (Human Usage)
base16 - 0123456789ABCDEF

2⁸ = 256 = 256/2 = -128 to -1 0 1 to 127 - byte

Datatype - Size, type of date store

Data Type	Size (Bytes)	Maxi and Mini Value Stored	Default Value
Byte	1	-128 to 127	0
Short	2	-32,768 to 32,767	0
Int	4	-2,147,483,648 (-2³¹) to 2,147,483,647 (2^31-1).	0
Long	8	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807	0L
Float	4	6 to 7 decimal point	0.0f
Double	8	15 decimal point	0.0d
Char	2	single character/letter or ASCII values is -128 to 127	'\u0000'
Boolean	1	true or false values	false

Bit - Binary Digit - 0, 1s

Base 2 - 0, 1

Base 8 - 01234567

Base 10 - 0123456789

Base 16 - 0123456789ABCDEF

ASCII - American Standard for Code Information Interchange

In Java, the default data type for numbers is "int".

Q&A

What is Variable?

In Java, variables are like storage boxes where we keep data.
Each variable has a type (like int, String, etc.) that tells what kind of data it can hold.
You can assign values to these variables and use them later in your program.
It is a name of the memory location.

Why should learning Datatypes?

They defines what type of data can be stored and manipulated in a program.
It ensures proper memory allocation or usage

What is data manipulation?

Data manipulation is the process of modifying or organizing data to make it more useful and to handle operations efficiently.

What is Data Types?

Data types are the kinds of values you can use in programming.
For example, numbers, text (strings), and true/false (boolean) are common data types.
They help the computer understand what kind of data it's working with.
It is useful for allocating memory for the data that is stored.
They define the maximum and minimum values that can be stored in the memory location.

What is a statically typed language, and can you give an example? (or) Why is Java considered a statically typed language?

In statically typed languages (like Java), the type of data a variable will hold is set during compile-time. Once set, it can't be changed.
Java is statically typed, so once you decide a variable's type (like int for numbers), it can't hold anything else.
Type checking occurs at compile time

Dynamically Typed Languages

Dynamic means that we can change the variable type after setting the particular type value to the particular variable. For example, the Python language is a dynamically typed language.
A variable in Python can store a string first, then an integer, without causing an error.
Type checking occurs at runtime or execution time

Difference Between Statically Typed Languages and Dynamically Typed Languages

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DataTypes and Variables - Obsidian Files - Obsidian v1.6.7 12-09-2024 20_28_35.png

What is Primitive Data Types?

Primitive data types are the most basic types of data in programming.
They hold simple, single values and not complex data.
There are a total of 8 primitive data types: byte, short, int, long, float, double, boolean, and char.
The size of these data types doesn't change across different operating systems, making Java platform-independent.

What is Non-Primitive Data Types?

Non-primitive data types are more complex and can hold multiple values.
Examples include arrays, classes, and objects.
They are created by the programmer and can store different types of data together.

What is Wrapper Class?

A wrapper class in Java is used to convert primitive data types (like int, char, boolean) into objects.
For example, Integer is the wrapper class for int.
This allows primitives to be treated as objects when needed, like in collections.
There are 8 wrapper classes in Java.
The wrapper class in Java package is java.lang.

What is auto-boxing?

Auto-boxing in Java is when the compiler automatically converts a primitive data type (like int) into its wrapper class object (like Integer).
It makes it easier to work with primitives in situations that need objects, like in lists or maps.

What is unboxing?

Unboxing is the reverse of auto-boxing in Java.
It automatically converts a wrapper class object (like Integer) back into a primitive data type (like int).
This happens when you need the primitive value from the object.

What is Unicode?
?

Unicode is a universal character encoding standard that allows computers to represent and handle text from any language.
It assigns a unique number (code point) to every character, symbol, or emoji, ensuring consistent text display across different systems and platforms.