Variable refers to a memory location. It is used to store data. The data of variable can be changed and reused depending on condition or on information passed to the program.
Kotlin variable is declared using keyword var and val.
The difference between var and val is specified later on this page.
Here, variable language is String type and variable salary is Int type. We don't require specifying the type of variable explicitly. Kotlin complier knows this by initilizer expression ("Java" is a String and 30000 is an Int value). This is called type inference in programming.
We can also explicitly specify the type of variable while declaring it.
It is not necessary to initialize variable at the time of its declaration. Variable can be initialized later on when the program is executed.
Difference between var and val
Here, the value of variable salary can be changed (from 30000 to 40000) because variable salary is declared using var keyword.
Here, we cannot re-assign the variable language from "Java" to "Kotlin" because the variable is declared using val keyword.