My First Encounter with Kotlin

Synopsis

I have heard a lot about Kotlin in the past but never got an opportunity to work with it on any of my projects. All this changed recently when I started working on a Mobile app centric project. so, I decided to get my hands dirty with Kotlin. I have extensive experience working on Java and have never been convinced to explore functional programming because of my addiction to Java

Introduction

HelloWorld Example

HelloWorld.java

public class HelloWorld {
    public static void main(String args[]){
        System.out.println("Say Hello");
    }
}

HelloWorld.kt

fun main(){
    println("Say Hello")
}

Java Bean Example

Employee.java

public class Employee {
    private String name;
    private String phone;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "name='" + name + '\'' +
                ", phone='" + phone + '\'' +
                '}';
    }
}

public class HelloWorld {
    public static void main(String args[]){
        Employee emp = new Employee();
        emp.setName("Emp1");
        emp.setPhone("222-999-222");

        System.out.println("Employee Name is " + emp.getName() + " and Phone No. is " + emp.getPhone());
    }
}

Now, the same JavaBean logic in Kotlin

Employee.kt

data class Employee (val name:String, val phone:String)

fun main(){
    val emp = Employee("Emp1", "222-999-222")
    val(name, phone) = emp
    println("Employee Name is $name and Phone No. is $phone")
}

Functions in Kotlin (Equivalent of methods in Java)

fun addNumber(num1: Int, num2: Int): Unit{
    println(num1+num2)
}

The return type “Unit” here can be compared to void in Java . Equivalent function with a return type will be as follows

fun addNumber(num1: Int, num2: Int): Int{
    return num1 + num2
}

This function makes num3 default value as 20, so num3 becomes an optional parameter in this function

fun addNumber(num1: Int, num2: Int, num3: Int = 20): Int{
    return num1 + num2 + num3
}

with named param, We may change the sequence in which parameters are passed E.g. the function above can be called as follows

addNumber(num1=10, num2=30, num3=40)
addNumber(num2=10, num2=30, num1=40)

A Simple class in Kotlin

fun main(){
    var hello1 = SimpleClass()
    hello1.sayHello()
}

class SimpleClass {
    fun sayHello(){
        println("Hi")
    }
}

or the same class with a constructor parameter

class SimpleClass constructor(var name: String){
    fun sayHello(){
        println("Hi " + name)
    }
}