Benefits of Kotlin

Statically typed programming language
for modern multiplatform applications

Statically Typed
//java
final String companyName = "0+X";
//kotlin
val companyName = "0+x"

Why Kotlin?
• Concise
• Safe
• Interoperable
• Tool-friendly

• Data Classes
• Null-safety
• Smart Casts
• High order functions
• Inline Functions
• Extension functions
• Standard Extension Functions

Classes
class Store(val name: String,
var address: String?)

public final class Store {
@NotNull
private final String name;
@Nullable
private String address;
@NotNull
public final String getName() {
return this.name;
}
@Nullable
public final String getAddress() {
return this.address;
}
public final void setAddress(@Nullable String var1) {
this.address = var1;
}
public Store(@NotNull String name, @Nullable String address) {
Intrinsics.checkParameterIsNotNull(name, "name");
super();
this.name = name;
this.address = address;
}
}

Data Classes
data class Store(val name: String,
var address: String?)

public final class Store {
@NotNull
private final String name;
@Nullable
@NotNull
public final String getName() {
return this.name;
}
@Nullable
}
}
public Store(@NotNull String name, @Nullable String address) {
super();
this.name = name;
this.address = address;
}
@NotNull
public final String component1() {
return this.name;
}
@Nullable
}
@NotNull
public final Store copy(@NotNull String name, @Nullable String address) {
return new Store(name, address);
}
// $FF: synthetic method
// $FF: bridge method
@NotNull
public static Store copy$default(Store var0, String var1, String var2, int var3, Object var4) {
if((var3 & 1) != 0) {
var1 = var0.name;
}
if((var3 & 2) != 0) {
var2 = var0.address;
}
return var0.copy(var1, var2);
}
public String toString() {
return "Store(name=" + this.name + ", address=" + this.address + ")";
}
public int hashCode() {
return (this.name != null?this.name.hashCode():0) * 31 + (this.address != null?this.address.hashCode():0);
}
public boolean equals(Object var1) {
if(this != var1) {
if(var1 instanceof Store) {
Store var2 = (Store)var1;
if(Intrinsics.areEqual(this.name, var2.name) && Intrinsics.areEqual(this.address, var2.address)) {
return true;
}
}
return false;
} else {
return true;
}
}
}

public String toString() {
return “Store(name=" + this.name + “, address=" + this.address +")";
}
public int hashCode() {
return (this.name != null?this.name.hashCode():0) * 31 + (this.address !=
null?this.address.hashCode():0);
}
public boolean equals(Object var1) {
if(this != var1) {
if(var1 instanceof Store) {
Store var2 = (Store)var1;
if(Intrinsics.areEqual(this.name, var2.name) && Intrinsics.areEqual(this.address,
var2.address)) {
return true;
}
}
return false;
} else {
return true;
}

componentN( )
@NotNull
return this.name;
}
@Nullable
}

Destructuring Declaration
val store = Store("ICA Nära", "Sveavägen 118")
val (name, address) = store
println(“$name address is $address") // prints "ICA Nära address is
Sveavägen 118 "
val map = hashMapOf(1 to "ICA Nära Sveavägen",
2 to "ICA Nära Hötorget”)
for ((i, n) in map){
println("Entry in map: $i: $n")
}

copy( )
@NotNull
public final Store copy(@NotNull String name, @Nullable String address) {
return new Store(name, address);
}
// $FF: synthetic method
// $FF: bridge method
@NotNull
public static Store copy$default(Store var0, String var1, String var2, int var3, Object var4) {
if((var3 & 1) != 0) {
var1 = var0.name;
}
if((var3 & 2) != 0) {
var2 = var0.address;
}
return var0.copy(var1, var2);
}

copy( )
val store = Store(name = "ICA Nära",address = "Sveavägen 118")
val store1 = store.copy()
// Store(name=ICA Nära, address=Sveavägen 118)
val store2 = store.copy(name = "ICA Kvantum")
// Store(name=ICA Maxi, address=Sveavägen 118)
val store3 = store.copy(address = null)
// Store(name=CA Nära, address=null)
val store4 = store.copy(name = "ICA Kvantum", address = "Solna Centrum")
// Store(name=ICA Kvantum, address=Solna Centrum)

Java fields and Kotlin
properties
//java
}
}
//kotlin
var address: String

Null Safety
// won't compile
var storeName:String = "ICA Kvantum"
storeName = null
var storeName1: String? = getName()
storeName1.length

Checking for null in
conditions
if (storeName != null && storeName.length > 0) {
print("String of length ${storeName.length}")
} else {
print("Empty string")
}

Safe calls
name?.length
store?.address?.city

!!operator
var storeName: String? = getString()
storeName!!.length

Null Safe Scoping
storeName?.let {
it.length
}

Elvis Operator
var storeName: String? = getString()
return storeName?.length ?: -1

Smart Casts
val mixedTypeList: List<Any> = listOf("I", "am", 5, "feet", 9.5, "inches", "tall")
for(value in mixedTypeList) {
if (value is String) {
println("String: '$value' of length ${value.length} ")
} else if (value is Int) {
println("Integer: '$value'")
} else if (value is Double) {
println("Double: '$value' with Ceil value ${Math.ceil(value)}")
} else {
println("Unknown Type")
}
}

Object obj = “Simple sample in JAVA”;
if(obj instanceof String) {
// Explicit Casting to `String`
String str = (String) obj;
System.out.println("Found a String of length " + str.length());
}

Smart Casts
//x is automatically cast to string on the right-hand side of `&&`
if (name is String && name.length > 0) {
print(name.length) // x is automatically cast to String
}

Unsafe cast operator as
val obj: Any = 123
val str: String = obj as String
// Throws java.lang.ClassCastException: java.lang.Integer cannot be cast to
java.lang.String
val obj: Any? = null
val str: String = obj as String
// Throws kotlin.TypeCastException: null cannot be cast to non-null type kotlin.String

Safe cast operator as?
val obj: Any? = null
val str: String? = obj as? String? // Works
println(str) // Prints null

High Order Functions
fun operate (v1: Int, v2: Int, fn: (Int, Int) -> Int): Int {
return fn (v1, v2)
}
fun sum (x1: Int, x2: Int) = x1 + x2
fun sub (x1: Int, x2: Int) = x1 - x2
println("The sum of 10 and 5 is ${operate (10, 5, ::sum)}")
println(“Sub… of 100 and 40 is ${operate (100, 40, ::sub)}")

Lambda expressions
return fn (v1, v2)
}
println("The sum of 10 and 5 is ${operate (2, 3,{x, y -> x+y})}")
println(“Sub… of 100 and 40 is ${operate (100,40,{x, y -> x-y})}”)
println(“Sub… of 100 and 40 is ${operate (100,40){x, y -> x-y}}")

Anonymous Functions
return fn (v1, v2)
}
println(“The sum of 10 and 5 is
${ operate (2, 3,fun(x1:Int, x2:Int):Int {return x1 + x2})}")
println ("Sub... of 100 and 40 is
${operate (100,40,fun(x:Int, y:Int) = x + y )}")

Inline Functions
inline fun operate(v1:Int, v2:Int, fn:(Int, Int)->Int):Int {
return fn (v1, v2)
}
println("The sum of 10 and 5 is ${operate (2, 3,x+y)}")

Extension Functions
fun String.upperCaseFirstLetter(): String {
return this.substring(0, 1).toUpperCase().plus(this.substring(1))
}
val name ="ica"
print(name.upperCaseFirstLetter())
public class StringUtilskt {
public static String upperCaseFirstLetter(String str) {
return str.substring(0, 1).toUpperCase() + str.substring(1);
}
}

apply
public inline fun <T> T.apply(block: T.() -> Unit): T { block(); return this }
fun openBankIdIntent(activity: Activity, autostartToken: String) {
val intent = Intent()
intent.`package` = "com.bankid.bus"
intent.action = Intent.ACTION_VIEW
intent.data = Uri.parse("bankid:///?autostarttoken=" + autostartToken + "&redirect=null")
activity.startActivity(intent)
}
fun Activity.openBankIdIntent(autoStartToken: String) {
val intent = Intent()
intent.apply {
`package` = "com.bankid.bus"
action = Intent.ACTION_VIEW
data = Uri.parse("bankid:///?autostarttoken=" + autostartToken + "&redirect=null")
}
this.startActivity(intent)
}

run
public inline fun <T, R> T.run(block: T.() -> R): R = block()
val generator = PasswordGenerator()
generator.length = 10
generator.lowers = false
generator.numbers = true
val password: Password = generator.generate()
val password: Password = PasswordGenerator().run {
length = 10
lowers = false
numbers = true
generate()
}

Let
public inline fun <T, R> T.let(block:(T)->R): R = block(this)
store?.let {
viewBinding.marketingName.text = store.marketingName
viewBinding.storeIcon.setImageResource(…)
}

How to start with Kotlin
• Online playground - http://try.kotl.in
• Converting a Java File to Kotlin File

Benefits of Kotlin

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