Kotlin operators in, it, is,

I'm a rookie with Kotlin and I can't differ between these three operators, do they have any relation between them? How's their comparison with Java?

Solution

No, there's no direct connection between them, other than being 2-letter keywords in Kotlin.

They're used for different things:

in is used to test whether one object is contained within another (syntactic sugar for contains() in Java):
```
if (someObject in someList) …
```
It's also used when iterating through a collection (where Java just uses :):
```
for (item in someList) …
```
And to specify that a type parameter is contravariant (where Java would use ? super):
```
interface List<in E>
```
it is used within a lambda that takes exactly one parameter, to refer to the parameter in a concise way without having to give it a name (with no direct Java equivalent):
```
someList.filter{ it < 10 }
```
is is used to test whether an object is of a given type (the same as instanceof in Java):
```
if (s is String) …
```

As @Adrian says, all the keywords are explained in the Kotlin reference documentation.