Kotlin | Theory

- ?? Kotlin is the primary language for Android app development and more.

- ?? This beginner's course by Muhammad Wajid Khan covers Kotlin comprehensively.

- ?? Ideal for complete beginners and experienced programmers alike.

- ??? Covers basics like software setup to advanced topics like object-oriented programming.

- ?? Uses engaging animations to explain concepts effectively.

- ?? Declaring a variable with val means its value cannot be changed later.

- ?? Use var to allow changing a variable's value.

- ??? Differentiate between String and Int types for storing text and whole numbers respectively.

- ?? Type inference in Kotlin allows omitting type declarations if the compiler can infer it.

- ?? IntelliJ IDEA uses type inference to determine variable types based on assigned values.

- ?? Kotlin's Int type has a specific range of values (e.g., integers) and limitations.

- ??? Use specific data types (`Byte`, Short, Long) for different ranges of whole numbers.

- ?? Understanding data type widths and memory usage helps optimize code and understand system constraints.

- ?? For floating-point numbers, Kotlin uses Float and Double to handle decimal numbers with different precision and storage capacities.

- ?? Kotlin variables are inferred; adding suffixes directly affects their type.

- ?? Introduction to Kotlin Char and Boolean data types for storing single characters and true/false values.

- ??? Project setup in IntelliJ for Kotlin, focusing on Pascal case naming conventions.

- ?? Declaring Char data types using val for immutability, demonstrating single character storage ('D').

- ??? Printing Char values to console using string interpolation in Kotlin.

- ?? Explanation of Boolean data type usage for logical control in program flow.

- ?? Recap on Kotlin's type inference, which automatically deduces variable types based on assigned values.

- ?? Overview of Kotlin's primitive data types: byte, short, int, long, float, double, char, boolean.

- ? Introduction to Kotlin operators: addition, subtraction, multiplication, division, modulus.

- ?? Increment and decrement operators (`++` and --) demonstrated with variable X initialization and usage.

- ?? Importance of operator precedence in Kotlin expressions, controlled by parentheses for prioritization.

- ?? Explains the usage of if-else statements in Kotlin.

- ?? Demonstrates how to handle conditions using if and else.

- ?? Shows how to chain multiple conditions using else if.

- ?? Illustrates comparisons with operators like greater than and less than.

- ?? Explains the logical operators && (and) and || (or).

- ?? Introduces using if-else as an expression to assign values.

- ?? Emphasizes the importance of using curly braces for clarity in code structure.

- ??? Use curly braces around expressions to execute multiple statements.

- ?? The logical not operator (`!`) can negate a boolean expression.

- ?? Use the when statement as an expression to assign values.

- ??? Always use curly braces for multiple lines of code in Kotlin.

- ?? Use the !! operator carefully to handle potential null pointer exceptions.

- ?? The Elvis operator (`?:`) helps handle null values by providing a default value.

- ?? Functions in Kotlin can take parameters to customize behavior.

- ?? Functions are reusable code blocks that can be called multiple times.

- ?? Multiple parameters can be defined for functions, separated by commas.

- ??? Define a function getMax to find the maximum of two integers a and b.

- ?? Use an if statement inside getMax to compare a and b.

- ?? Ensure proper formatting and type declaration (`int`) for parameters and return type.

- ?? Demonstrate calling getMax with arguments (`5` and 9).

- ??? Capture and print the result using println.

- ?? Discuss the impact of return in functions, highlighting how it stops further code execution.

- ?? Explain function overloading with different types (`int` and double) and additional parameters.

- ?? Showcase default parameters for a function sendMessage, allowing optional message input.

- ?? Utilize named parameters (`message` and name) to selectively assign values to parameters irrespective of order.

- ?? Discuss the use of vararg to handle variable numbers of parameters in a function, like sum, to calculate the sum of multiple integers.

- ?? Looping Mechanism: Demonstrates different ways to loop in Kotlin using for, while, and do-while loops.

- ?? Range Usage: Explains using ranges (`1..10` and 1 until 10) to control loop boundaries and behaviors.

- ?? Step Variation: Introduces arbitrary step (`step 2`) in loops to skip numbers during iterations.

- ? Exclusion with 'until': Highlights how until excludes the upper limit (`1 until 10`) in loops.

- ?? Loop Direction: Discusses looping direction and constraints (`10 downTo 1`) in Kotlin.

- ?? Reverse Looping: Shows how to loop in reverse using downTo keyword (`10 downTo 1`).

- ?? Stepwise Looping: Demonstrates looping with a step (`1..10 step 2`) to skip values during iterations.

- ?? Nested Loops: Illustrates nesting loops (`while` inside while) and their execution flow.

- ?? Break Statement: Explains the use of break to exit loops prematurely based on conditions.

- ? Continue Statement: Shows how continue skips current iteration and proceeds to the next in loops.

- ?? The code iterates over numbers and outputs even numbers to the console.

- ?? It uses conditional checks with continue to skip odd numbers.

- ?? Refactored using single-expression functions and the modulus operator for even number detection.

- ?? Demonstrates the use of for loops for iterating through numbers.

- ?? Introduces arrays and their declaration in Kotlin, with examples of mixed type arrays.

- ?? Explains array indexing and accessing elements using square brackets.

- ?? Shows how to retrieve the size of an array using .size.

- ?? Utilizes loops (`for`) to iterate over arrays and conditional (`if`) checks with is keyword for type checking.

- ?? Implements functions to find maximum and minimum values in an integer array.

- ?? Combines the two functions into a single function using a Boolean parameter to determine whether to find the maximum or minimum value.

- ??? Summarizes the process of using a return statement to exit a function early based on conditions.

- ?? Describes how a loop iterates through numbers to find a minimum value based on comparisons.

- ?? Introduces object-oriented programming concepts, focusing on classes and objects as representations of real-world entities.

- ??? Demonstrates creating a class Car with properties (`name`, model, color, doors) and methods (`move`, stop).

- ?? Discusses the use of constructors to initialize object properties efficiently, replacing direct assignments post object creation.

- ??? Create a user object with customizable properties using Kotlin.

- ?? Define a primary constructor to initialize the user object with parameters like name, last name, and age.

- ?? Use initializer blocks to validate and conditionally assign values to properties based on input conditions.

- ?? Demonstrate how to implement default parameter values for properties within the primary constructor.

- ??? Implement secondary constructors to handle cases where default values are assigned if not all parameters are provided.

- ??? Discuss the benefits of using secondary constructors for executing additional code during object creation.

- ?? Highlight the flexibility of Kotlin in managing constructor overloads and default values for object properties.

- ??? The code includes redundant quad declarations.

- ?? Unnecessary code that duplicates functionality provided by Kotlin's built-in features.

- ?? Scotland already generates implicit code, but you can override it manually.

- ?? Demonstrates how to customize getter behavior to prepend "first name" to property values.

- ??? Shows a print statement for setter behavior when assigning values.

- ?? The field identifier prevents infinite recursion in setter calls.

- ?? Explains why using field instead of first name in setters avoids recursion.

- ?? Demonstrates a recursive setter error caused by calling itself indefinitely.

- ?? Emphasizes that field is restricted to getters and setters to prevent similar errors.

- ?? Compares getters and setters to explicit functions for updating and retrieving properties.

- ?? The object keyword in Kotlin creates a Singleton instance.

- ?? Singleton ensures only one instance exists throughout the application.

- ??? No constructors are used in Singleton, just curly braces for initialization.

- ?? Initializer blocks in Singleton execute once during instance creation.

- ??? Example: object Database { init { println("Database created") } }

- ?? Lazy initialization delays object creation until it's accessed.

- ??? Example: val lazyDatabase by lazy { Database }

- ?? Enum classes represent fixed sets of values, can have properties and methods.

- ?? Example: enum class Direction { NORTH, SOUTH, EAST, WEST }

- ?? Loop through enums with values() method and for loop.

- ?? Access enum properties like .name and custom properties/methods.

- ?? Inner classes in Kotlin are declared inside other classes.

- ?? Example: class Outer { inner class Inner { /* ... */ } }

- ?? Challenge: Create a bank account class with deposit, withdraw, and balance functions.

- ??? private ensures that properties cannot be accessed outside of the class.

- ?? By making properties private, direct data changes outside the class are prevented.

- ?? The compiler recognizes that private properties are only interacted with through specific class functions (`deposit`, withdraw, calculateBalance).

- ??? When defining a primary constructor, private properties are automatically inferred due to their restricted usage.

- ?? Inheritance: Inheritance allows creating new classes (`Car`, Plane) using existing classes (`Vehicle`). It enables inheriting functions and properties, facilitating code reuse.

- ?? Base classes (`Vehicle`) provide shared functionality, avoiding duplicate code in subclasses (`Car`, Plane).

- ?? Inheritance supports overriding functions (`move`) to customize behavior (`flying` for Plane).

- ??? Example demonstrates creating specific classes (`Button`, RoundButton) inheriting from a generic class (`View`) to enhance code reusability and specificity in programming.

- ?? Kotlin's sealed classes ensure exhaustive when expressions, requiring all possible cases to be handled to avoid compilation errors.

- ?? Adding all possible branches (`result`, error, success) ensures exhaustive handling of scenarios in sealed classes.

- ?? Defining functions inside a sealed class like showMessage ensures all subclasses handle necessary cases.

- ?? Sealed classes allow creating nested subclasses (`progress`) that enforce exhaustive handling across all scenarios.

- ?? Compared to enums, sealed classes offer more flexibility with nested subclasses and automatic exhaustive checks.

- ?? Abstract classes in Kotlin allow defining properties and abstract functions, needing inheritance for instantiation.

- ?? Overriding equals, hashCode, and toString in data classes ensures proper structural equality and representation.

- ?? Data classes simplify object comparison by automatically generating equals, hashCode, and toString methods based on properties.

- ?? The tutorial discusses implementing interfaces in Kotlin classes to define shared behaviors.

- ?? It demonstrates how to override the toString() method in Kotlin to customize object string representations.

- ?? Explains using the data keyword in Kotlin to automatically generate equals(), hashCode(), and toString() methods for data classes.

- ?? Shows practical use of interfaces in Android Studio, linking UI elements to Kotlin code using setOnClickListener.

- ??? Illustrates creating an Android emulator to test UI button functionality linked via Kotlin code.

- ?? Implemented the "one click" function for each object, making it specific to each button.

- ?? Used object expressions (anonymous classes) for this purpose, allowing instantiation and implementation in place.

- ?? Explained delegation in Kotlin, highlighting its use to delegate authority from one class to another, useful when multiple inheritance isn't possible.

- ?? Demonstrated delegation with interfaces A and B, showing how classes can inherit behavior from multiple interfaces using the by keyword.

- ?? Used delegation with properties, showing how to override getValue and setValue to customize behavior when getting and setting values.

- ?? Discussed collections, focusing on lists, sets, and maps in Kotlin.

- ?? Detailed the difference between mutable and immutable collections, showing examples of each.

- ?? Introduced transformations in collections, starting with mapping to transform elements by a specified function (like multiplying each element by 10 in a set).

- ?? We can create pairs: "fox" and "red", "bear" and "brown", "wolf" and "gray" using the zip function.

- ??? Two ways to print colors and animals in pairs using zip: colors.zip(animals) or colors.zip(animals) { color, animal -> ... }.

- ?? unzip function used to separate pairs into individual collections after zip.

- ??? associateWith function creates a map where collection elements are keys and values are transformations (e.g., uppercase first letter).

- ??? associateBy function builds a map where transformations on values define keys and values (e.g., first letter uppercase, value length).

- ?? flatten function converts nested collections into a single-dimensional array for easier handling.

- ?? Functions like joinToString provide customizable string representations of collections with separators, prefixes, and postfixes.

- ?? Using limit and truncated in joinToString limits the number of elements displayed and specifies the trailing text for truncated collections.

- ?? Slice Function:

- Explains slicing a collection based on indices or a range.

- Demonstrates using slice to select specific elements from a collection.

- Shows how slice works with steps to skip elements.

- ?? Take and Drop Functions:

- Covers take to select elements from the start and takeLast for the end.

- Illustrates drop to exclude elements from the start and dropLast for the end.

- Shows practical examples of using these functions with predicates.

- ?? Take While and Drop While:

- Introduces takeWhile to select elements until a condition is false.

- Explains dropWhile to exclude elements until a condition is false.

- Demonstrates usage with predicates to conditionally filter elements.

- ?? Chunked Function:

- Describes chunked for breaking a collection into fixed-size chunks.

- Provides an example of chunking a list into chunks of three elements each.

Each section explains Kotlin's collection operations clearly, with practical examples to demonstrate their usage.

- ?? Summarize aggregate operations in Kotlin collections:

- Kotlin collections offer functions like minOrNull and maxOrNull for finding smallest and largest elements.

- average computes the average value of collection elements.

- sum returns the sum of numeric collection elements.

- count provides the count of elements in the collection.

- ?? Demonstrate usage with a sample list:

- Created a list numbers containing integers.

- Used functions sum, count, average, minOrNull, and maxOrNull to compute respective values.

- Output displayed the computed results for sum, count, average, min, and max values of the list.

- ?? Explore advanced use of sumOf:

- Introduced sumOf function with a transformation.

- Demonstrated multiplying each element by 2 using sumOf.

- ?? Introduce sorting with sorted:

- Used sorted to sort numbers in ascending order.

- Explained how sorted works using the Comparable interface implemented by integers.

- ?? Implement custom sorting with Comparator:

- Defined a Comparator for sorting objects based on RAM size.

- Sorted a list of custom objects (`laptops`) based on RAM using sortedWith.

- ?? Simplify sorting with sortedBy:

- Simplified sorting using Lambda expressions with sortedBy.

- Sorted lists by price and RAM size using sortedBy.

- ?? Highlight benefits of concise code:

- Emphasized how Lambda functions (`sortedBy`) reduce complexity and improve readability.

- Showed how to chain sorting criteria using sortedWith and thenBy.

These bulleted summaries encapsulate the main concepts and practical examples covered in the given text.

- ?? Binary search efficiently finds elements in a sorted collection by dividing the list in half at each step.

- ?? It continually adjusts its search range based on whether the middle element is greater or less than the target.

- ? Using generics in Kotlin allows type-safe collections, ensuring only specified types are stored.

- ?? Example: Creating a generic Team class allows adding players of specific types like FootballPlayer and BaseballPlayer.

- ?? Upper bounds in generics restrict types that can be used, enforcing inheritance from a specified class like Player.

- ?? Generics in Kotlin improve code consistency and prevent runtime errors by resolving types at compile time.