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Java Variables and Data Types

Summary - Java Variables and Data Types

Variables in Java

What is a Variable?

A container for storing information, reducing redundancy in code.

Naming Conventions

Variables can start with an underscore (_), dollar sign ($), or letter, and include numbers, underscores, and dollar signs.

Cannot start with numbers, contain spaces, or be reserved keywords.

CamelCase Style

First word lowercase, subsequent words capitalized (e.g., sumOfNumbers).

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Introduction to Data Types

Declaring and Initializing Variables

Declaration: Specify data type and variable name.

Initialization: Assign a value to the variable.

Primary Data Types

Integer: Whole numbers (byte, short, int, long).

Floating Point: Decimal numbers (float, double).

Character: Symbols and letters (char).

Boolean: True/false values (boolean).

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Character & Boolean Data Types

Character (char)

Symbols and letters, enclosed in single quotes ('A').

Boolean (boolean)

True or false values.

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Storing Char and Bool Data Types

ASCII and Unicode

ASCII: Encodes characters in 7 or 8 bits, limited to 128 symbols.

Unicode: Supports over a million characters, using 1 to 32 bits.

UTF-8: Most common format, 1 to 4 bytes.

Boolean Values

Represented as 1 (true) and 0 (false).

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Integer Data Type

Two’s Complement

Method for storing negative numbers in binary.

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Floating Point Numbers

Basics

Float: 4 bytes (32 bits), smaller decimals.

Double: 8 bytes (64 bits), higher precision.

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Common Mistakes with Float

Precision Issues

Floating-point numbers can't always be exactly represented in binary, causing precision errors.

Solution: Tolerance Value

Use a tolerance value (epsilon) for accurate comparisons.

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Overflow and Underflow

Overflow

Value exceeds data type limit, wraps around to minimum value.

Underflow

Value goes below data type limit, wraps around to maximum value.

Real-World Example: YouTube's View Counter

Upgraded to a 64-bit integer to avoid overflow issues.

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Understanding TypeCasting

Widening Type Casting

Automatic conversion to a higher data type.

Narrowing Type Casting

Manual conversion to a lower data type, potentially losing precision.

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Representing Floating Point Numbers

Scientific Notation

Simplifies representation of large and small numbers using mantissa and exponent.

Normalization

Standardizes number representation for efficient storage and precise calculations.

Exponent Biasing

Converts signed exponents into an unsigned form for easier storage and computation.

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Common Mistakes: With Float

Precision Issues

Floating-point arithmetic can result in rounding errors.

Solution: Tolerance Value

Use a tolerance value (epsilon) for accurate comparisons.

These concepts of Java variables and data types are very useful for understanding core Java. For more detailed information, refer to the Notion link:

Java Variables and Data Types⁠

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