It's time for Kotlin

@kkondzielski

Agenda

  • What is Kotlin?
  • #1 Type inference
  • #2 Data structures
  • #3 Default parameters
  • #4 Null safety
  • #5 Extenion functions
  • #6 Lazy intialization
  • #7 Operator overloading

What is kotlin?

  • Statically typed programming language
    for the JVM

What is kotlin?

  • Statically typed programming language
    for the JVM
  • Developed by JetBrains

What is kotlin?

  • Statically typed programming language
    for the JVM
  • Developed by JetBrains
  • 100% interoperability with Java

What is kotlin?

  • Statically typed programming language
    for the JVM
  • Developed by JetBrains
  • 100% interoperability with Java
  • It targets JVM 6

What is kotlin?

  • Statically typed programming language
    for the JVM
  • Developed by JetBrains
  • 100% interoperability with Java
  • It targets JVM 6
  • Supports functional programming with zero-overhead lambdas

#1 Type inference

#1 Type inference

String firstName = "Adam";
char middle = 'c';
String lastName = "Brown";
int age = 15;

Map<String,List<String>> fruitsColors = new HashMap<>();
List<String> colors = new ArrayList<>();
colors.add("red");
colors.add("green");
fruitsColors.put("apple", colors);

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#1 Type inference

val firstName = "Adam" // String
val middle = 'c'  // Character
val lastName = "Brown" // String
val age = 15 // Integer
val fruitsColors = mapOf("apple" to listOf("red", "green"))

String firstName = "Adam";
char middle = 'c';
String lastName = "Brown";
int age = 15;

Map<String,List<String>> fruitsColors = new HashMap<>();
List<String> colors = new ArrayList<>();
colors.add("red");
colors.add("green");
fruitsColors.put("apple", colors);

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A

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T

#2 Data structures

#2 Data structures

public class JavaUser {
    public final String firstName;
    public final String lastName;
    public final Integer age;

    public JavaUser(String firstName, String lastName, Integer age) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        JavaUser javaUser = (JavaUser) o;

        if (!firstName.equals(javaUser.firstName)) return false;
        if (!lastName.equals(javaUser.lastName)) return false;
        return age.equals(javaUser.age);

    }

    @Override
    public int hashCode() {
        int result = firstName.hashCode();
        result = 31 * result + lastName.hashCode();
        result = 31 * result + age.hashCode();
        return result;
    }

    @Override
    public String toString() {
        return "JavaUser{" +
                "firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", age=" + age +
                '}';
    }
}

#2 Data structures

public class JavaUser {
    public final String firstName;
    public final String lastName;
    public final Integer age;

    public JavaUser(String firstName, String lastName, Integer age) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        JavaUser javaUser = (JavaUser) o;

        if (!firstName.equals(javaUser.firstName)) return false;
        if (!lastName.equals(javaUser.lastName)) return false;
        return age.equals(javaUser.age);

    }

    @Override
    public int hashCode() {
        int result = firstName.hashCode();
        result = 31 * result + lastName.hashCode();
        result = 31 * result + age.hashCode();
        return result;
    }

    @Override
    public String toString() {
        return "JavaUser{" +
                "firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", age=" + age +
                '}';
    }
}

data class KotlinUser(val firstName: String,
                      val lastName: String,
                      val age: Int)

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#3 Default parameters

JavaUser createUserWithFirstName(String firstName) {
        return new JavaUser(firstName, "Brown", 15);
    }

JavaUser createUserWithLastName(String lastName) {
    return new JavaUser("Jacob", lastName, 15);
}

createUserWithFirstName("Alan")
createUserWithLastName("Jones")

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#3 Default parameters

JavaUser createUserWithFirstName(String firstName) {
        return new JavaUser(firstName, "Brown", 15);
    }

JavaUser createUserWithLastName(String lastName) {
    return new JavaUser("Jacob", lastName, 15);
}

createUserWithFirstName("Alan")
createUserWithLastName("Jones")
fun createUser(firstName: String = "Adam",
               lastName: String = "Brown",
               age: Int = 15): KotlinUser {
    return KotlinUser(firstName, lastName, age)
}

createUser(firstName = "Jacob")
createUser(lastName = "Jones")
createUser(age = 25, firstName = "Alan")

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#4 Null safety

interface Person {

    Person getFather();
    String getName();
}

class FatherNameDisplayer {

    public String display(Person person) {
        Person father = person.getFather();
        if (father != null) {
            String name = father.getName();
            return name;
        }
        return "Name not known";
    }
}

JAVA

#4 Nullsafety

interface Person {

    Person getFather();
    String getName();
}

class FatherNameDisplayer {

    public String display(Person person) {
        Person father = person.getFather();
        if (father != null) {
            String name = father.getName();
            return name;
        }
        return "Name not known";
    }
}
interface Person {

    fun getFather(): Person?
    fun getName(): String?
}

JAVA

KT

#4 Nullsafety

interface Person {

    Person getFather();
    String getName();
}

class FatherNameDisplayer {

    public String display(Person person) {
        Person father = person.getFather();
        if (father != null) {
            String name = father.getName();
            return name;
        }
        return "Name not known";
    }
}
interface Person {

    fun getFather(): Person?
    fun getName(): String?
}

class FatherNameDisplayer {

    fun display(person: Person): String {
        val father = person.getFather()
        if (father != null) {
            val name = father.getName()
            return name //HERE!!!
        }
        return "Name not known"
    }
}

JAVA

KT

#4 Nullsafety

interface Person {

    Person getFather();
    String getName();
}

class FatherNameDisplayer {

    public String display(Person person) {
        Person father = person.getFather();
        if (father != null) {
            String name = father.getName();
            return name;
        }
        return "Name not known";
    }
}
interface Person {

    fun getFather(): Person?
    fun getName(): String?
}

class FatherNameDisplayer {

     fun display(person: Person)
          = person.getFather()?.getName() 
            ?: "Name not known"
}

JAVA

KT

#5 Extension functions

 Integer max = Collections.max(list);
 Integer result = Collections.binarySearch(otherList, max);

JAVA

#5 Extension functions

 Integer max = Collections.max(list);
 Integer result = Collections.binarySearch(otherList, max);
val max = list.max();
val result = otherList.binarySearch(max);

JAVA

KT

#5 Extension functions

 Integer max = Collections.max(list);
 Integer result = Collections.binarySearch(otherList, max);
val max = list.max();
val result = otherList.binarySearch(max);

JAVA

KT

fun List<Int>.max(): Int? {
    return Collections.max(this)
}

#6 Lazy initialization

public class MainActivity extends AppCompatActivity {
    
    private MainController controller;

    @Override
    void onCreate() {
        super.onCreate();
        controller = new MainController(getIntent());
        controller.onCreate()
    }

    @Override
    void onDestroy() {
        controller.onDestroy();
        super.onDestroy();
    }
}

JAVA

#6 Lazy initialization

public class MainActivity extends AppCompatActivity {
    
    private MainController controller;

    @Override
    void onCreate() {
        super.onCreate();
        controller = new MainController(getIntent());
        controller.onCreate()
    }

    @Override
    void onDestroy() {
        controller.onDestroy();
        super.onDestroy();
    }
}
class KotlinActivity : AppCompatActivity() {

    private val controller by lazy { 
        MainController(getIntent())
    }

    override fun onCreate() {
        super.onCreate()
        controller.onCreate()
    }

    override fun onDestroy() {
        controller.onDestroy()
        super.onDestroy()
    }
}

JAVA

KT

#7 operators overloading

static <T> List<T> merge(List<T> first, List<T> second) {
    List<T> results = new ArrayList<T>();
    results.addAll(first);
    results.addAll(second);
    return results;
}

JAVA

#7 operators overloading

static <T> List<T> merge(List<T> first, List<T> second) {
    List<T> results = new ArrayList<T>();
    results.addAll(first);
    results.addAll(second);
    return results;
} 
val results = listOf(1,3) + listOf(2,5)

JAVA

KT

#7 operators overloading

static <T> List<T> merge(List<T> first, List<T> second) {
    List<T> results = new ArrayList<T>();
    results.addAll(first);
    results.addAll(second);
    return results;
} 
val results = listOf(1,3) + listOf(2,5)

JAVA

KT

operator fun <T> Collection<T>.plus(elements: Iterable<T>): List<T>

Thank You

Questions?

@kkondzielski

Kotlin

By Pablo Arqueros

Source: Kasper Kondzielski

Kotlin

  • 91

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