Kotlin_TutorialPoints Flashcards
Language type?
Strongly typed
OOP
Functional
When is Kotlin made official language for Adroid Dev?
2017
Prerequisites
Knowledge of JAVA, OOP and Class(es)
Kotlin VS Java
Kotlin: Open Source Software More expressive Less boiler plate Better preformance
Kotlin Functions
Allowed to be declared at the top level
Declarations?
Doesn’t need to be Static
Be careful - can cause problems for Devs coming from Java
Hello World .kt
fun main(args: Array){
println("Hello, World")
}How does run Code on the JVM (Java Virtual Machine)?
byte code!
Similar to Java’s (.class)
Byte code behavior when in the same JVM?
They can communicate with eachother
How does Kotlin translate into JavaScript?
.kt file is converted into ES5.1
Declaring a ‘character’?
Assigning it?
Printing it?
val letter: Char
letter = ‘A’
println(“$letter”)
Declaring Boolean?
val letter: Boolean
letter = true
println(“Your character value is “+”$letter”)
Declaring Strings?
var rawString :String
val escapedString : String
Declaring Arrays?
val numbers: IntArray = intArray(1,2,3,4,5)
Types of Collections
Immutable Collection - cannot be edited
Mutable Collection - can be edited
Collection Caution
Kotlin system does not represent a difference between the 2 Types
Collection - Mutable
val numbers: MutableLIst = mutableListOf(1,2,3)
Collection - Immutable
val readOnlyView: List = numbers
Adding item to Mutable Collection
.add(item)
Collection Functions
first( ) - gets first elem
last( ) - gets last
filter( ) - filters through collection
How does Ranges work in Kotlin?
rangeTo( )
or (. .)
if(i in 1..10) //same as 1<=i && i < = 10
if - else
if ( ) {
//code
} else {
//otherwise code
}Use of When
val x:Int = 5
when (x) {
1 -> print(“x = = 1”)
2 -> print(“x = = 2”)
else -> { // Note the block
print("x is neither 1 nor 2")
} }
For Loop
val items = listOf((1,2,3,4)
for (i in items) println(‘values of the array” +i)
For loop - looping, index and item at that index
val items = listOf(1, 22, 83, 4)
for ((index, value) in items.withIndex()) {
println(“the element at $index is $value”)
}
While - standard loop
while(x <=10){
println( x )
x++
}
Return
Return is a keyword that returns some value to the calling function from the called function.
Continue & Break
Continue & Break − Continue and break are the most vital part of a logical problem. The “break” keyword terminates the controller flow if some condition has failed and “continue” does the opposite
Example Function declaration
fun doubleMe(x:Int):Int {
return 2*x;
}What does a break with a Label on it look like?
myLabel@
break@myLabel
OOP - 1st line - declaration
class myClass{
}
Declaring a private variable within a Class
private var name: String = “Tutorials.point”
val VS var
val - cannot be changed
var - can be changed
What is a Nested Class?
A class that has been created inside another class.
What is true about the default attribute fora Nested Class?
It is Static Can be accessed without creating any class of that class
How does Kotlin access a Nested Class?
val demo = Outer.Nested.foo( )
print (demo)
class Outer{
class Nested{
fun foo () = "Welcome"
}
}
//demo - printed out? // Welcome
How does an Inner Class work?
val demo = Outer().Nested().foo() // calling nested class method print(demo)
class Outer {
class Nested {
fun foo() = "Welcome to The TutorialsPoint.com"
}
}
//========
Uses an Obj declaration and uses the inner Class to access a private val
Anonymous Inner Class is…
The concept of creating an object of interface using runtime object reference is known as anonymous class
What are Type Aliases?
A property of Kotlin compiler
Provides the flexibility of creating a new name of an Existing Type
Types of constructors in Kotlin?
- primary constructor
2. secondary constructor
Rules about Kotlin class(es) and constructors?
Kotlin class can have one (1) primary constructor and (1 or 1+) secondary constructor
Java VS Kotlin - constructors?
Java constructor - initializes the member variables
Kotlin constructor - the primary constructor initializes the class, where as the secondary constructor; helps to include logic while initializing the same
Kotlin Primary constructor - declared how?
Primary constructor can be declared at class header level!
Kotlin Primary Constructor - Example
class Person(val firstName: String, var age: Int){
//class bodyHow to init a new Class?
val / var person1 = Person(name, birthday)
Kotlin - primary constructor
Only declared in the head/beginning of Class
Kotlin - secondary constructor
Needs ‘constructor’ keyword
Can be implemented 1 or more times
Inheritance in Kotlin?
Base class is named “Any”
“Any” is the…
Super class of the ‘any’ default class declared in Kotline
Kotlin inheritance keyword?
”:”
To override a function?
override fun example( )
Kotlin Interface - keyword meaning?
Define an interface in Kotlin as shown in the following piece of code.
[visibility] interface InterfaceName [extends other interfaces] {
constant declarations
abstract method declarations
}
Uses of interface(s)
Being able to use an object without knowing its type of class,
Limitation of Kotlin?
It doesn’t support multiple inheritances, however (!) the same thing can be achevied by implementing more than two interfaces at a time
In Kotlin - what are the 4 different ‘Access modifiers’?
Private
Protected
Internal
Public
Private (Access modifier)
when declared Private - only available within immediate scope
Protected (Access modifier)
Not available for top level declaration; protected class or interface is visible to it’s subclass only
Internal (Access modifier)
New to Kotlin(!) If marked as Internal -then that specific file will be in the internal field. Internal package - only available inside the module under which it is implemented Internal class - only viewable to by other class(es) in the same package or module
Public (Access modifier)
Public modifier is accessible from anywhere in the project.
If no Access modifier is specified - autos to Public
Extension
Allows you to define a method outside the main class. To test some code - without affecting the other
Extension for Objejcts
Uses the ‘companion’ keyword.
Define a Data Class
A type of class that is used to hold data and does not do much else
Data Class
Just a function to allow for Objects to be initialized and populated
“Sealed” Class
- Used to represent a restricted hierarchy.
- Allows the developers to maintain a data type.
- Need to use the Sealed keyword
- Sealed class can have its own subclass, butt they must all be in the same Kotlin file
Generics
Usually written - t for template
Kotlin - class VS type
- List is a class
- List is a type
Generic - behavior
Allows for different types of data to be accessed and used
Want to assign the generic type to super type?
Use “out” keyword.
Want to assign the generic type to sub-type?
Use “in” keyword
What keyword shows Kotlin’s “delegation” design patter?
"by" Using this keyword or delegation methodology, Kotlin allows the derived class to access all the implemented public methods of an interface through a specific object
Delegation means?
Passing the responsibility to another class or method
What to do when a property is already declared in some places?
Reuse the same code to initialize them
What is a lambda function?
A function type to represent functions, and provides a set of specialized language constructs
What is a higher-order function?
A higher-order function is a function that takes functions as parameters, or returns a function.
Function types in Kotlin
Kotlin uses function types, such as (Int) -> String
Using Lazy( )
Lazy( ) - is a lambda function. It will return Lazy, where is basically the type of the properties using it
Delegaton.Observerable()
Takes 3 arguments to initialize the obj and returns the same to the called function
General Syntax
get( ), set( )
getValue( ), setValue( )
How to declare a Function?
fun myFunction
Fun - example
fun main(args: Array) {
println(MyFunction("tutorialsPoint.com"))
}
fun MyFunction(x: String): String {
var c:String = "Hey!! Welcome To ---"
return (c+x)
}Syntax of Fun
fun (:):
Lambda Function (?)
Lambda is a high level function that drastically reduces the boiler plate code while declaring a function and defining the same
Inline Function
pass a lambda to another function to get our output which makes the calling function an inline function
Declaring Multiple variables
val (name, age) = person
Real World - Destructing Declarations
fun main(args: Array) {
val s = Student("TutorialsPoint.com","Kotlin")
val (name,subject) = s
println("You are learning "+subject+" from "+name)
}
data class Student( val a :String,val b: String ){
var name:String = a
var subject:String = b
}Exception Handling
try {
// does this code work?
} catch(e: Exception) {
// what error tripped?
} finally {
// always run this
}
