Kotlin basic in android

Kotlin basic information for developers

Val: val is immutable variable type means non-changeable value. We say in other words this is same as the final keyword in java.

Var : var is mutable variable type means changeable value.

Lateinit: lateinit is late initialization. This is used with var variable and non-nullable initialization. Lateinit is global initialization. Allow initialization a non-null property outside of a constructor

Lazy: Basically lazy use with val variable. Like 

val name =String by lazy{“samset”}

Difference between lateinit and lazy?

 Both are the delay the property of initialization but lateinit modifier use with only var variable and lazy use with val variable. val is define run time property.

What is default visibility access modifier?

Public is default access modifier.
Public,internal,protected,private

Does the following inheritance structure is compile?

Class A{}

Class B:A(){

}

No, By default classes are final in kotlin. To make them non-final, you need to add the open modifier.

How is the type of constructor in kotlin?

Two type
1: Primary -> Theses are defined in the class headers. They can not hold any logic. They are only one constructor per classes.
2: Secondary-> They are defined in the class body. They can hold logic There is more than one secondary constructor.

What is the init block in kotlin?

Init block is initializer block in kotlin.It is executed at once after initializing primary constructor.

What is the type of argument in the constructor?

By default the constructor holds val but you can change explicitly in var.

What is the data class in kotlin?

Data class is a simple getter setter class that be provide toString(), hash() and copy() method.

What is the difference between inline and infix functions?

Inline function is used to save memory overhead by preventing object to allocations. It provides the function body.  This increases the bytecode slightly but saves a lot of memory.

Infix function is other use to call the function without parentheses or brackets.

How to create a singleton class in kotlin?

To use object the pattern for our class we must use the keyword.
object MyClass{}

Does kotlin have the static keyword?

No, To create a static method in kotlin we use the companion object.

Class A{

companion object

{

 fun myMethod(): Int =5

}

 }

Internal : Declare and visible and accessible in current module.

Open: Allow subclassing a class or overriding members.

Sealed : Restricted to subclassing.

Const: Const is compile-time variable. Const can be used with var.When add cont with val this is work as a compile-time variable. This is use with only val variable and string and primitive data type. This is like static keyword in java.