I am trying to learn Kotlin. What is
internal in Kotlin compared to Java?
RadioGroup radioGroup; RadioButton button; Button submit;
After converting it shows:
internal var radioGroup: RadioGroup internal var button: RadioButton internal var submit: Button
var are the two keywords you can use to declare variables (and properties). The difference is that using
val gives you a read-only variable, which is the same as using the
final keyword in Java.
var x = 10 // int x = 10; val y = 25 // final int y = 25;
val whenever you can is the convention in Kotlin, and you should only make something a
var if you know that you’ll be changing its value somewhere.
internal is a visibility modifier that doesn’t exist in Java. It marks a member of a class that will only be visible within the module it’s in. This is a similar visibility to what the default
package visibility gives you in Java (which is why the converter would use it when converting members with
package visibility). However, it’s not exactly the same. Also, note that it’s not the default visibility in Kotlin, classes and their members in Kotlin are
public by default.
There is more in the documentation about visiblity modifiers.
val : immutable data variable
var : mutable data variable
When you converted your Java code to Kotlin:
A converter found that you have not initialised variables, so it made them
var(mutable) as you will initialise them later.
Probably your variables are unused, so the converter made them internal, guessing you will not use them outside of your package.
val use to declare final variable. Characteristics of val variables
- Must be initialized
- value can not be changed or reassign
var is as a general variable
We can initialize later by using lateinit modifier
lateinitalso use for global variable we can not use it for local variable]
- value can be changed or reassign but not in global scope
val in kotlin is like final keyword in java
In kotlin we can declare variable in two types:
val cannot be reassigned, it works as a final variable.
val x = 2 x=3 // cannot be reassigned
On the other side, var can be reassigned it is mutable
var x = 2 x=3 // can be reassigned