Android
Activity lifecycle
Activity lifecycle.
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Code From Scratch Series
Blog — Code From Scratch
Deep technical articles on Android engineering, Kotlin internals, and software systems. Based on the Code From Scratch YouTube series.
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Android
Android platform overview
Android platform overview.
Read →Android Runtime
ANR — why it happens and what the system does
Have you ever seen that dreaded dialog? The one that says
Read →Android Runtime
App startup — from tap to first frame
You tap an icon on your phone. A fraction of a second later, an app appears. It feels instant — or at least it
Read →Memory
Caching — when it helps, when it kills you
Caching feels like a cheat code. You fetch something expensive — a network response, a database query, a decod
Read →Concurrency
Channels
Channels.
Read →Kotlin
Classes and objects
Classes and objects.
Read →Data & Types
Collections
Collections.
Read →Data & Types
Composite types
Composite types.
Read →Failure & Resilience
Consistency vs availability — the trade-off you always make
We have reached the final video in this course, and I saved one of the most important concepts for last. Every
Read →Concurrency
Context switching — the hidden cost of multitasking
In the last video we learned that threads are data structures the kernel manages, and that the scheduler rapid
Read →Kotlin
Control flow in Kotlin
Control flow in Kotlin.
Read →Concurrency
Coroutine context and dispatchers
Coroutine context and dispatchers.
Read →Concurrency
Coroutines — what the compiler actually generates
You have probably heard it said that coroutines are lightweight threads. And while that gives you a useful men
Read →Performance
CPU-bound vs IO-bound — knowing the difference changes everything
If there is one concept in this entire course that will immediately change how you write concurrent code, it i
Read →Data & Types
Data and types
Data and types.
Read →Data & Types
Data validation
Data validation.
Read →Foundations
Decisions and branches
Decisions and branches.
Read →Android
Dependency injection
Dependency injection.
Read →Concurrency
Dispatchers and scheduling — where your code runs
You now know that coroutines are state machines that suspend and resume, borrowing threads from pools rather t
Read →Performance
EAGLE-4 does not run on a Mac. I measured MTP instead: +92% on one model, -19% on another
I measured MTP speculative decoding on an Apple M2 Ultra: +92% on a dense 27B model, -19% on a 35B MoE model.
Read →Concurrency
Error handling in coroutines
Error handling in coroutines.
Read →Foundations
Errors and failure
Errors and failure.
Read →Kotlin
Extension functions
Extension functions.
Read →Concurrency
Flow basics
Flow basics.
Read →Concurrency
Flow operators
Flow operators.
Read →Kotlin
Functions
Functions.
Read →Execution Model
Garbage collection — how the runtime cleans up after you
Have you ever wondered what happens to all the objects you create in Kotlin? You call constructors all day lon
Read →Execution Model
Heap, stack, and where your objects live
Quick question for you. When you write val user equals User parentheses in Kotlin, where does that object actu
Read →Execution Model
How code actually executes
Have you ever stopped to think about what actually happens when you tap
Read →Failure & Resilience
Idempotency — why repeating an action must be safe
Imagine this scenario. A user opens your app, taps
Read →Data & Types
Immutability
Immutability.
Read →Kotlin
Inheritance and interfaces
Inheritance and interfaces.
Read →Foundations
Input and output
Input and output.
Read →Concurrency
Introduction to coroutines
Introduction to coroutines.
Read →Android
Jetpack Compose basics
Jetpack Compose basics.
Read →Kotlin
Kotlin collections
Kotlin collections.
Read →Kotlin
Kotlin fundamentals
Kotlin fundamentals.
Read →Kotlin
Kotlin type system
Kotlin type system.
Read →Kotlin
Lambdas and higher-order functions
Lambdas and higher-order functions.
Read →Architecture
Layers — when they help, when they are overhead
Layers are the most fundamental concept in software architecture. Every architecture you have ever seen is bas
Read →Execution Model
Memory allocation — what "new" really does
How many objects do you think your app creates in a single second? Ten? A hundred? Try tens of thousands. Ever
Read →Concurrency
Memory visibility — happens-before and the JMM
In the last video we talked about race conditions, where two threads interleave their operations and produce w
Read →Data & Types
Modeling with data
Modeling with data.
Read →Architecture
Modularization — the cost nobody talks about
Modularization is one of those topics where the benefits are loudly celebrated and the costs are quietly endur
Read →Memory
Mutability vs immutability — what actually happens in memory
Every Kotlin developer knows the difference between val and var. Val means you cannot reassign it. Var means y
Read →Foundations
Naming and abstraction
Naming and abstraction.
Read →Android
Navigation
Navigation.
Read →Android
Network requests
Network requests.
Read →Data & Types
Null and absence
Null and absence.
Read →Memory
Object graphs and references — why memory leaks happen
Memory leaks. Every Android developer dreads them. You see the warnings in your profiler, maybe LeakCanary pop
Read →Networking
Offline-first — designing for no network
Here is a question for you. How often do your users have no network? If you said
Read →Failure & Resilience
Partial failures — most things fail partially, not completely
When we think about failure in software, we tend to think in binary terms. It either worked or it did not. The
Read →Data & Types
Primitive types
Primitive types.
Read →Android Runtime
Process death — your app is killed more than you think
I want to tell you about the single most common source of bugs in Android apps. It is not null pointer excepti
Read →Performance
Profiling — reading traces, not guessing
In the last two videos, we talked about where time is actually spent and the difference between CPU-bound and
Read →Concurrency
Race conditions — why shared state breaks
Here is a simple problem. You have a variable called counter, it starts at zero, and you have two threads. Eac
Read →Performance
Real optimization — what works, what is myth
We have spent three videos building up the tools and concepts you need: where time is spent, the CPU-bound ver
Read →Foundations
Repetition
Repetition.
Read →Android
Repository pattern
Repository pattern.
Read →Networking
Retries, backoff, and timeouts — failure is normal
Here is something that will change how you think about networking: failure is not an edge case. Failure is the
Read →Android
Room database
Room database.
Read →Kotlin
Scope functions
Scope functions.
Read →Foundations
Sequence and order
Sequence and order.
Read →Kotlin
Sequences
Sequences.
Read →Networking
Serialization — the cost of converting data
Your server sends JSON. Your app needs Kotlin objects. Something has to convert between the two. You probably
Read →Concurrency
Shared state problems
Shared state problems.
Read →Foundations
State and change
State and change.
Read →Android
State in Compose
State in Compose.
Read →Architecture
State management — the real trade-offs
MVI, MVVM, MVC. If you have been in Android development for a while, you have probably seen passionate debates
Read →Memory
Strings, buffers, and copies — the cost nobody measures
Here is a question I want you to sit with for a moment. How many String objects does your app create when it p
Read →Concurrency
Structured concurrency
Structured concurrency.
Read →Concurrency
Suspend functions
Suspend functions.
Read →Concurrency
Synchronization
Synchronization.
Read →Networking
TCP, HTTP, and latency — where time goes
In the last video, we traced a single API call and saw that it takes around 500 milliseconds just to get a res
Read →Android
Testing on Android
Testing on Android.
Read →Execution Model
The call stack — what happens when you call a function
Have you ever wondered what actually happens inside your phone's processor the instant you call a function? No
Read →Android Runtime
The main thread, Looper, and Handler
Every Android developer knows one rule: do not block the main thread. But do you actually know what the main t
Read →Android Runtime
The rendering pipeline — measure, layout, draw
You write a TextView in XML or call Text in Compose, and text appears on screen. Simple, right? But think abou
Read →Concurrency
Threads
Threads.
Read →Concurrency
Threads — what they are at the OS level
You use threads every single day. Every Android app you have ever built runs on threads. Your main thread draw
Read →Failure & Resilience
Timeouts and retries — getting them right
Every time your app makes a network call, it is placing a bet. It is betting that the server will respond with
Read →Kotlin
Variables and values
Variables and values.
Read →Android
ViewModel
ViewModel.
Read →Android
Views and layouts
Views and layouts.
Read →Memory
WeakReferences, SoftReferences — what the GC sees
We have talked about how the garbage collector traces from roots, following references to decide what stays al
Read →Networking
What happens when you call an API
You have written this code a hundred times. You define a Retrofit interface, you call getUser, you get back a
Read →Foundations
What is a program?
What is a program?
Read →Concurrency
What is concurrency
What is concurrency.
Read →Architecture
When NOT to abstract
Abstraction is the most celebrated tool in software engineering. We are taught from day one: do not repeat you
Read →Performance
Where time is actually spent
Performance optimization is one of the most satisfying things you can do as a developer. You find the slow thi
Read →Architecture
Why Clean Architecture fails in practice
If you have been in Android development for more than a year, you have almost certainly encountered Clean Arch
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