Kotlin introductory notes (I) kotlin variables and non variables

Preface : This tutorial is best done with JAVA Study on the basis of

One 、 Variable

Kotlin Excellent type derivation mechanism

•  val ：(value Abbreviation ) Used to declare an immutable variable , This variable cannot be re assigned after the initial assignment , Corresponding Java Medium final Variable .
•  var ：(variable Abbreviation ) Used to declare a variable , This kind of variable can still be re assigned after the initial assignment , Corresponding Java Non - final Variable .

Such as :

fun main() {
    val num = 666
    println("num = " + num)
}

there num It is automatically deduced into Int ( notes ：kotlin Abandoned int, All use object data types   Such as :Int)

however , If we delay the assignment of a variable ,kotlin You can't automatically deduce , We need to use the following method

Kotlin You can display declared variables

val num:Int = 10

We explicitly declare variables num by Int type , here Kotlin Don't try type derivation anymore .

Java and Kotlin Data type comparison table

Java Basic data type	Kotlin data type	Data type description
int	Int	integer
long	Long	Long integer
short	Short	Short
float	Float	Single-precision floating-point
double	Double	Double precision floating point
boolean	Boolean	Boolean type
char	Char	Character
byte	Byte	Character

Kotlin The small white , When learning the works of teacher Guolin , Take notes . If there are any mistakes, please point out ！ Thank you for reading ！

Reference resources ：《 First line of code Android ( The third edition )》   --- Guo Lin