Succumb to the Kotlin side

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Who am I?

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Acknowledge

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Index

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Constructors class Person {}

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Constructors class Person constructor(firstName: String) {}

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Constructors class Person(firstName: String) {} (if no annotations or visibility modifiers)

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Constructors class Person(firstName: String) { init { //We can use/initialize firstName here } }

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Constructors class Person(val firstName: String) {}

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Constructors class Person(val firstName: String = "Alberto") {}

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Constructors data class Person(val firstName: String = "Alberto"){}

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Constructors data class Person(val firstName: String = "Alberto"){} ● equals()/hashCode() ● toString() of the form "Person(firstName=Alberto)" ● componentN() functions ● copy()

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Constructors data class Person(val firstName: String = "Alberto"){} // val alberto = Person() val joe = Person("Joe")

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Constructors data class Person(val firstName: String = "Alberto"){} // val alberto = Person() val joe = Person("Joe") Ok, but...

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Constructors data class Person(val firstName: String = "Alberto"){} // val alberto = Person() val joe = Person("Joe") Where´s the “new”?

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Constructors data class Person(val firstName: String = "Alberto"){} // val alberto = Person() val joe = Person("Joe") Where´s the “new”? and the semicolon!?

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Functions fun read(items: Array, offset: Int = 0, length: Int = items.size()) { // ... }

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Functions fun read(items: Array, offset: Int = 0, length: Int = items.size()) { // ... } read(ArrayOf(1, 2, 3))

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Functions fun read(items: Array, offset: Int = 0, length: Int = items.size()) { // ... } read(ArrayOf(1, 2, 3), length = 1)

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Control flow (I) var max: Int if (a > b) //do some stuff max = a else //do some stuff max = b

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Control flow (I) var max: Int if (a > b) //do some stuff max = a else //do some stuff max = b (but… if is now an expression)

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Control flow (I) var max = if (a > b) //do some stuff a else //do some stuff b (if branches can be blocks, and the last expression is the value of a block)

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Control flow (I) var max = if (a > b) a else b (and for simpler ifs...)

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Control flow (I) var max = if (a > b) a else b

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Control flow (II) switch (x) { 1 -> print("x is 1") 2 -> print("x is 2") }

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Control flow (II) switch (x) { 1 -> print("x is 1") 2 -> print("x is 2") }

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Control flow (II) when (x) { 1 -> print("x is 1") 2 -> print("x is 2") }

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Control flow (II) when (x) { 0, 1 -> print("x is 0 or 1") 2 -> print("x is 2") }

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Control flow (II) when (x) { in 1..10 -> print("x is in the range") in validNumbers -> print("x is valid") !in 10..20 -> print("x is outside the range") else -> print("none of the above") } (validNumbers is a collection)

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Control flow (II) val hasPrefix = when(x) { is String -> x.startsWith("prefix") else -> false } (since here when is an expression we’re forced to put the else)

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Control flow (II) val hasPrefix = when(x) { is String -> x.startsWith("prefix") else -> false } (since here when is an expression we’re forced to put the else)

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Control flow (extra) if (obj is String) { // At this point obj is magically a String! print(obj.length) }

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Null safety var a: String = "abc" a = null a.capitalize()

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Null safety var a: String = "abc" a = null a.capitalize() Kotlin Quiz a) NullPointerException

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Null safety var a: String = "abc" a = null a.capitalize() Kotlin Quiz a) NullPointerException b) Compilation error

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Null safety var a: String = "abc" a = null a.capitalize() Kotlin Quiz a) NullPointerException b) Compilation error c) Nothing, the method won´t be executed

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Null safety var a: String = "abc" a = null a.capitalize() Kotlin Quiz a) NullPointerException b) Compilation error c) Nothing, the method won´t be executed d) Assertion error

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Null safety var a: String = "abc" a = null a.capitalize() Kotlin Quiz a) NullPointerException b) Compilation error c) Nothing, the method won´t be executed d) Assertion error e) I really think it´s a NullPointerException

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Null safety var a: String = "abc" a = null // compilation error a.capitalize()

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Null safety var a: String? = "abc" a = null a.capitalize()

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Null safety var a: String? = "abc" a = null a.capitalize() // compilation error

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Null safety var a: String? = "abc" a = null if (a != null) { a.capitalize() }

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Null safety var a: String? = "abc" a = null if (a != null) { // boring a.capitalize() }

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Null safety var a: String? = "abc" a = null if (a != null) { // boring a.capitalize() } // 3 lines

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Null safety var a: String? = "abc" a = null if (a != null) { // boring a.capitalize()// 17 characters for a null-check } // 3 lines

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Null safety var a: String? = "abc" a = null a?.capitalize()

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Null safety var a: String? = "abc" a = null a ?.capitalize()

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Null safety var a: String? = "abc" a = null a ?.capitalize() // 1 char

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Null safety var a: String? = "abc" a = null a ?.capitalize() // 1 char, 16 less than before :)

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Null safety var a: String? = "abc" var b = if (a != null) { a.capitalize() } else { "" }

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Null safety var a: String? = "abc" var b = a?.capitalize() else ""

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Null safety var a: String? = "abc" var b = a?.capitalize() else ""

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Null safety var a: String? = "abc" var b = a?.capitalize() ?: ""

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Null safety var a: String? = "abc" var b = a?.capitalize() ?: ""

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Static

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Static Doesn’t exist

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Static Doesn’t exist Bye utils?

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Static Doesn’t exist Bye singleton? Bye utils?

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Object window.addMouseListener(object : MouseAdapter() { override fun mouseClicked(e: MouseEvent) { // ... } } // This is an Object expression

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Object object StuffManager { fun registerStuff(stuff: Stuff) { // ... } val allStuffs: Collection get() = // ... } // This is an Object declaration

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Object object StuffManager { fun registerStuff(stuff: Stuff) { // ... } val allStuffs: Collection get() = // ... } // This is an Object declaration Hello singleton!

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Object class MyClass { companion object { fun getSomeUtilStuff() { //... } } } Hello utils

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Object class MyClass { companion object { fun getSomeUtilStuff() { //... } } } Hello utils?

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Extension Functions // Java code public static void hideImage(ImageView image) { image.setVisibility(View.GONE); image.setImageResource(0); } UiUtils.hideImage(new ImageView(context));

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Extension Functions // Kotlin magic fun ImageView.hide() { visibility = View.GONE setImageResource(0) }

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Extension Functions // Kotlin magic fun ImageView.hide() { visibility = View.GONE setImageResource(0) } // import com.xing.core.extensions.hide ImageView(context).hide()

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Higher-Order Functions fun logException(func: () -> T): T? { try { return func() } catch (ignored: Throwable) { Log.e("ERROR", "...") return null } }

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Higher-Order Functions fun logException(func: () -> T) = try { return func() } catch (ignored: Throwable) { Log.e("ERROR", "...") return null }

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Higher-Order Functions inline fun logException(func: () -> T) = try { return func() } catch (ignored: Throwable) { Log.e("ERROR", "...") return null }

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Higher-Order Functions inline fun logException(func: () -> T) = try { return func() } catch (ignored: Throwable) { Log.e("ERROR", "...") return null } // ... logException({ myDangerousMethod() })

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Higher-Order Functions inline fun logException(func: () -> T) = try { return func() } catch (ignored: Throwable) { Log.e("ERROR", "...") return null } // ... logException { myDangerousMethod() }

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Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) val edit = prefs.edit() edit.putBoolean("enabled", true) edit.commit()

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Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) // in some method... edit("enabled", true) fun edit(key: String, value: Boolean) { prefs.edit().putBoolean(key, value).commit() }

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Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) // in some method... edit("enabledCount", 1) fun edit(key: String, value: Boolean) { prefs.edit().putBoolean(key, value).commit() }

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Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) // in some method... edit("enabledCount", 1F) fun edit(key: String, value: Boolean) { prefs.edit().putBoolean(key, value).commit() } fun edit(key: String, value: Int) { prefs.edit().putInt(key, value).commit() }

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Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) // in some method... edit("enabledCount", 1L) fun edit(key: String, value: Boolean) { prefs.edit().putBoolean(key, value).commit() } fun edit(key: String, value: Int) { prefs.edit().putInt(key, value).commit() } fun edit(key: String, value: Float) { prefs.edit().putFloat(key, value).commit() }

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Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: () -> Unit) { val editor = edit() func() editor.commit() }

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Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: () -> Unit) { val editor = edit() func() editor.commit() } prefs.inEdit { prefs.putBoolean(...) }

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Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: () -> Unit) { val editor = edit() func() editor.commit() } prefs.inEdit { prefs.putBoolean(...) }

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Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: (SharedPreferences.Editor) -> Unit) { val editor = edit() func() editor.commit() } prefs.inEdit { prefs.putBoolean(...) }

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Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: (SharedPreferences.Editor) -> Unit) { val editor = edit() func(editor) editor.commit() } prefs.inEdit { prefs.putBoolean(...) }

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Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: SharedPreferences.Editor.() -> Unit) { val editor = edit() func(editor) editor.commit() } prefs.inEdit { it.putBoolean(...) }

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Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: SharedPreferences.Editor.() -> Unit) { val editor = edit() editor.func() editor.commit() } prefs.inEdit { it.putBoolean(...) }

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And more...

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And more... Because… why not?

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Android extensions import kotlinx.android.synthetic.main.activity_main.* class MyActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // Instead of findView(R.id.textView) as TextView textView.text = "Hello, world!" } }

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Examples (1) Bundle args = getArguments() if (args != null) { String data = args.getString(DATA_ARG) if (data != null) { data.getBytes() } }

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Examples (1) Bundle args = getArguments() if (args != null) { String data = args.getString(DATA_ARG) if (data != null) { data.getBytes() } }

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Examples (1) getArguments()?.getString(DATA_ARG)?.getBytes()

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Examples (2) imm = getContext().getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager imm.hideSoftInputFromWindow(yourEditText.getWindowToken(), 0)

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Examples (2) fun View.hideKeyboard() { imm = getContext().getSystemService( Context.INPUT_METHOD_SERVICE) as InputMethodManager imm.hideSoftInputFromWindow(getWindowToken(), 0) }

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Examples (2) fun View.hideKeyboard() { imm = getContext().getSystemService( Context.INPUT_METHOD_SERVICE) as InputMethodManager imm.hideSoftInputFromWindow(getWindowToken(), 0) } yourEditText.hideKeyboard()

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Examples (3) Bundle bigBundle = Bundle() bigBundle.putString(/**/) bigBundle.putInt(/**/) bigBundle.putString(/**/) bigBundle.putString(/**/)

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Examples (3) Bundle bigBundle = Bundle() bigBundle.apply { putString(/**/) putInt(/**/) putString(/**/) putString(/**/) //… }

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What can be optimized ● Every Utils class ● Duplicated boilerplate code ○ Model classes ○ Actions we do in single objects (Picasso) ● Whenever you have to write the same word multiple times (almost)