Everything in Android & Kotlin, page 21
CoroutineScope: The Parent of Your Coroutines
A CoroutineScope acts as a parent to a group of coroutines, managing their lifecycles. When the parent scope is cancelled, all its children are cancelled too. It's used with builders like launch to group related work, like in an Android ViewModel.
Coroutine Dispatchers: Telling Your Coroutines Which Thread to Use
A Dispatcher tells a coroutine which thread or thread pool to use for its work. Use Dispatchers.Default for CPU-intensive tasks. If none is specified, it inherits from its parent. The main footgun: Unconfined can resume on an unexpected thread.
Kotlin Coroutines on Android
Kotlin coroutines let Android code write asynchronous logic that reads like sequential code, suspending instead of blocking a thread. Structured concurrency ties each coroutine to a scope, so a destroyed ViewModel cancels its children automatically.
Kotlin Sealed Classes: Enums for Types
A sealed class is like an enum, but for types. It defines a closed set of subclasses, letting each one carry different data. It's perfect for modeling states like Loading, Success, and Error, ensuring you handle every case at compile time.
Kotlin Scope Functions: Cleaner Code, Clearer Choices
Kotlin's scope functions (let, run, apply) create a temporary workspace for an object, avoiding repetitive variable names. Use them for object configuration or chaining calls.
Kotlin Extension Functions: Add Methods Without Inheritance
Kotlin extension functions let you add new functionality to existing classes without inheritance, as if you were adding a new method. They're perfect for creating helpers for third-party library classes or framework types like String.
Kotlin Data Classes: Automatic Boilerplate for Data Holders
A Kotlin data class automatically generates boilerplate like equals() and toString() for classes that just hold data. Use it for model objects or DTOs where value equality matters. The footgun: its copy() method is shallow, sharing mutable objects.
Kotlin Inheritance: Open for Extension, Closed by Default
In Kotlin, classes are final by default. Think of inheritance as an opt-in feature you enable with the open keyword. Use it to create specialized versions of a base class, like a Student from a Person.
Kotlin Functions: Named, Reusable Code Blocks
A function is a named recipe for your code. You give it ingredients (parameters) and it produces a result. They are used everywhere, from calculating values to handling button clicks.
Kotlin Null Safety: Catch Nulls at Compile Time
Kotlin's type system catches null pointer errors at compile time. Variables are non-nullable by default; you must opt-in to nulls with a ? (e.g., String?). The compiler then forces you to handle the null case. The main footgun is the !! operator.
Kotlin Variables: `val` for Constants, `var` for Variables
In Kotlin, val creates a read-only constant you assign once, like a fixed setting. var creates a mutable variable you can change later. Always prefer val unless you explicitly need to reassign a value to prevent accidental state changes.
We are hiring for this. Every open role lists the topics its interview covers, so you can prepare for the real thing rather than guessing.
See open roles