travisdachi

fun attack(target: Target): Unit {}

fun attack(target: Target) {}

// fun <funName>(<parameterName>: <parameterType>): <returnType> [ = <singleExpression>]

travisdachi

fun fetchSomething(someId: String, callback: (Something) -> Unit) {
    val something = ...
    callback(something)
}

fetchSomething("anotherId", { something ->
    something.doSomething()
})

fetchSomething("someOtherId") {

travisdachi

//Java version
view.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        //do something
    }
});

//Kotlin version
view.setOnClickListener {

travisdachi

class SomeActivity : Activity() {
    val f: Foo by lazy { createFoo() } // put your initialization block here
  
    fun onCreate(bundle: Bundle?) {
        f.foo() // f will be created here and it's a val so you can't change it
        f // or you can call a getter just to initialize it
    }
    
    fun createFoo() = Foo(this)
    // this is useful when you need a context after the activity is created

travisdachi

data class Present(var id: String = "", var toy: String = "", var kid: String = "", var given: Boolean = false)

val list: MutableList<Present> = mutableListOf(
    Present("p0", "Dinosaur Figure", "Ralph", true),
    Present("p1", "Teddy Bear", "Ginger"),
    Present("p2", "Teddy Bear", "Cherry")
)
list[3] = Present("p3", "Pony Plush", "Cherry")

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for (p in list) println(p)
list.forEach { println(it) }

// Taken from Kotlin standard library
public inline fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit {
    for (element in this) action(element)
}

for (i in 0..list.size - 1) println("list[$i]: ${list[i]}")
for (i in list.indices) println("list[$i]: ${list[i]}")

travisdachi

val filtrate: List<Present> = list.filter { it.kid == "Cherry" }
// filtrate contains 2 elements which are p2 and p3

travisdachi

val kids: List<String> = list.map { it.kid }
// kids = [Ralph, Ginger, Cherry, Cherry]

travisdachi

val g: Map<String, List<Present>> = list.groupBy { it.kid }
/*
{
    Ralph=[Present(id=p0, toy=Dinosaur Figure, kid=Ralph, given=true)],
    Ginger=[Present(id=p1, toy=Teddy Bear, kid=Ginger, given=false)],
    Cherry=[Present(id=p2, toy=Teddy Bear, kid=Cherry, given=false), Present(id=p3, toy=Pony Plush, kid=Cherry, given=false)]
}
*/

travisdachi

val m: MutableMap<String, String> = mutableMapOf(
    Pair("one", "1"),
    "two" to "2"
)

println(m["two"])

m["three"] = "3"

m.forEach { println("${it.key}: ${it.value}") }