Advanced Kotlin Tips on writing good Kotlin code and using what the language has to offer. There are many benefits of using Kotlin; it is concise, safe and most importantly it is 100% interoperable with Java. It also tries to solve some of the limitations of Java.Now is a good time to consider Kotlin for your next big feature or project, because Google finally announced it to be a first-class language for writing Android apps in Google I/O 17.
Implementing lazy loaded and thread-safe singletons in Kotlin is really easy, unlike Java where you would have to rely on the complex double-checked locking pattern. And although Java enum singletons are thread-safe, they are not lazy loaded.
You must see this : Kotlin Parcelize – Developer need to know
object Singleton {
var s: String? = null
}
Contrary to a Kotlin class, an object can’t have any constructor, but init blocks can be used if some initialization code is required.
Singleton.s = "test" // class is initialized at this point
The object will be instantiated and its init blocks will be executed lazily upon first access, in a thread-safe way.
Favor Kotlin top-level extension functions over the typical Java utility classes. And for easier consumption within Java code, use 
// Use this annotation so you can call it from Java code like StringUtil.
@file:JvmName("StringUtil")
fun String.lengthIsEven(): Boolean = length % 2 == 0
val lengthIsEven = "someString".lengthIsEven()
Use apply to group object initialization statements to allow for cleaner, easier to read code.
// Don't
val textView = TextView(this)
textView.visibility = View.VISIBLE
textView.text = "test"
// Do
val textView = TextView(this).apply {
visibility = View.VISIBLE
text = "test"
}
let()Using let() can be a concise alternative for if. Check out the following code:
val listWithNulls: List<String?> = listOf("A", null)
for (item in listWithNulls) {
if (item != null) {
println(item!!)
}
}
With let(), there is no need for an if.
val listWithNulls: List<String?> = listOf("A", null)
for (item in listWithNulls) {
item?.let { println(it) } // prints A and ignores null
}
