Programming Concepts

Question 1

When, if/else as an expression

Answer 1

The body must return a value but you don’t have to use return statement:
val name = if (condition) {
body 1
} else { condition
body 2
}

val name = when (parameter) {
condition 1 → body 1
condition 2 → body 2
condition 3 → body 3
}

Question 2

Lambda expression

Answer 2

Shorthand syntax to declare function without fun keyword. You can store a lambda expression directly in a variable

val variableName ={
lambda expression
}

variableName () - to call it

Question 3

?.

Answer 3

Save call operator
nullableVariable ?. method / property

Stops any attempt off member access to null references and return null

Question 4

!!.

Answer 4

Not null assertion operator
nullableVariable!!. method / property

You assert that the value is not null

Question 5

, - in when statement

Answer 5

To separate multiple conditions

condition 1, condition 2

Question 6

in in when statement

Answer 6

in 1…10

Question 7

is in when statement

Answer 7

To check the data type

is type → body 1

Question 8

?:

Answer 8

Elvis operator to add default value when there is indeed null
val name = nullableVariable?.method ?: defaultValue

Question 9

Class in Kotlin

Answer 9

ClassName {
Properties
Methods
Constructors
}

ClassName () - to create an object
ClassObj.methodName() - to call class method

Question 10

Getter and setter functions

Answer 10

F.e.
var speakerVolume = 2
get () = field
set ( value ){
field = value
}

Variable read-only (val) don’t have set functions

Question 11

Constructor

Answer 11

Primary - class can have only one, defined as a part of a class header
ClassName constructor() { body}
Secondary - class can have multiple with or without parameters. If the class have primary each secondary must implement it. Enclose in the class body

Question 12

Open class

Answer 12

Informs the compiler that this class is extendable

Question 13

Inheritance

Answer 13

SubclassName ( optional parameters) : superclass (optional parameters) {
Body
}

To override functions:
- in superclass: open fun
- in subclass override fun
this same can be used for properties

Super - to reuse superclass code in subclass

var objName : superClassName = subclassName () - object of subclass

Question 14

Visibility modifiers

Answer 14

• public (default) accessible everywhere
• private accessible in the same class or source file
• protected accessible in subclass
• internal accessible in this same module

Modifier var name: date type = initial value
Modifier class name { body }

Question 15

Module

Answer 15

A collection of source files and build settings that let you divide your project into discrete units of funcionality

Question 16

Package

Answer 16

A directory or folder that groups related classes, a module can contain multiple packages

Question 17

Functions as data type

Answer 17

They can be stored in variables, passed into functions and returned from functions.

To store a function in variable and refer to it as value use :: ( function reference operator )

val variable = :: functionName

val name:() → Unit ={
body
}

Question 18

Lambda expression with parameters

Answer 18

Names in order that they occurs
val functionName = { param1, param2 →
function body
}

When it has only one parameter be can omit its name and use it

Question 19

Function with return type

Answer 19

funcName (optional parameters) → returnType {
body
}

If return type is nothing () → Unit

Question 20

Function as a return type

Answer 20

fun functionName (): functionType {
return nameOfAnotherFunc
}

Question 21

Passing a function as a parameter to other function

Answer 21

If this function has marcumeters too no names only types after comma

fun funcName ( paramName : type, funcName : (paramType, …) → returnType) : () → Unit { }

Question 22

Trailing lambda syntax

Answer 22

When a function type is a last parameter
f.e. trickOrTreate(false) lambda expression

Question 23

repeat()

Answer 23

Function to express for loop
repeat( times) {
…
}

Question 24

random ()

Answer 24

To get random number
var result = (1..6).random()

Question 25

Text Field ( )

Answer 25

Composable function that lets user enter text in an app
Value = “ “ test box that displays string value you pass here
onValueChange ={} lambda callback that is triggered when the user enters texts in text box =it

Question 26

State

Answer 26

Any value that can change over time. The only way to modify the composition is through recomposition. Compose needs to know which state to track so it can schedule the recomposition when it receives an update.

Question 27

mutableStateOf()

Answer 27

Function to create observable mutable state il receive an initial value

Question 28

keyboardOptions

Answer 28

keyboardOptions = KeyboardOptions.

An option to configure the keyboard display on the screen to enter f.e. digits, email, password

Question 29

getCurrencyInstance()

Answer 29

To display as currency
NumberFormat.getCurrencyInstance().format(variable)

Question 30

variable.toDoubleOrNull

Answer 30

Change string to double or null if it can not to double

Question 31

State hosting

Answer 31

Defining state in a way that you can reuse and share yours composable. Use it when:
- you need to share state with multiple composable functions
- create a stateless composable that can be reused in app
This often means introducing to parameters to the composable:
1. value: T // current value to display
2. onValueChanged: (T) → Unit // callback lambda which is triggered when the value changes so that the state can be updated elsewhere

Question 32

%s

Answer 32

Placeholder for string

Question 33

Keyboard action button

Answer 33

Button at the end of keyboard (search, send, go, next, done)
f.e.
keyboardOptions = KeyboardOptions.Default.copy( keyboardType.Number, imeAction = ImeAction.Next)

Question 34

Switch

Answer 34

Components: track, thumb, icon

Switch (
checked = // state of switch composable, whether the switch is checked
onCheckedChange = // the callback to be called when the switch is clicked
)

Question 35

Kotlin.match.ceil()

Answer 35

Round up function

Question 36

Automated tests types

Answer 36

• local tests directly tests a small piece of code to ensure that it works properly, you can test class, function or properties. Executed on your work station
• instrumentation tests a UI test for parts of app that depend on the Android API and its platform API’s and services. You launch au app simulate user interaction and checked whether the app reacted properly.
  The test code is build into its om Android application package (APK)

Question 37

Local test rules

Answer 37

• written in form of method - strictly check an expected output for a given input
• annotate with @Test
• name clearly describe what the test is for
• typically end with assertion which is used to ensure that given condition is met: assertEquals(), assertNotEquals(), assertNotTrue(), assertFalse(), assertNull(), assertNotNull(), assertThat()

Question 38

Class with generic

Answer 38

When you want a property to have different date types depending on the specific use case

ClassName < generic data type >( properties ) - data type is provided when instantiating the class

val instanceName = ClassName < actual data type > (parameters)

Question 39

Enum class

Answer 39

Is used to create types with limited set of possible values ( each called enum constant )
EnumClassName {
case1, case 2, case 3
}

To refer to enum constant: enumName.caseName

You can use it as data type in other class property
ClassName (
val name : enumClassName
)

Question 40

Data class

Answer 40

Contain only data without any methods, defining it allows compiler to make some assumptions and to automatically implement some methods f.e. toString(), equals () , hashCode(), copy(). Needs to have at least one parameter in its constructor. All constructor parameters must be marked with var or val. It can not be: open, abstract, sealed or inner.

DataClassName ( )

Question 41

Singleton object

Answer 41

When you want a class to have only one instance
object Name {
class body
}
It can’t have constructor, you can’t create instance directly. All the properties are defined within the curly braces and are given an initial value.

To access: objectName.propertyName