Demonstration of kotlin

App.kt

fun main(args: Array<String>)
{
    val users = listOf(
        User(username = "will",   isAdmin = true),
        User(username = "james",  isAdmin = true),
        User(username = "aneesh", isAdmin = true),
        User(username = "usain"),
        User(username = "michael")
    )

    val admins = users.filter { user -> user.isAdmin }
    val adminPairs = admins
        .flatMap   { admin -> admins.map { Pair(admin, it) } }
        .filterNot { pair  -> pair.first == pair.second }

    adminPairs.forEach { pair ->
        pair.first.greet(pair.second)
    }
}

data class User(val username: String, val isAdmin: Boolean)
{
    constructor(username: String) : this(username, isAdmin = false)

    fun greet(other: User)
    {
        println("Hello ${other.username}, I am ${this.username}")
    }
}