drulabs

val blank = "    ".isBlank()                      // true
val first = "Kaushal.Dhruw".substringBefore('.')  // "Kaushal"
val last = "Kaushal.Dhruw".substringAfter('.')    // "Dhruw"
val addSpaces = "1".padStart(2)                   // " 1"
val addSpacesEnd = "1".padEnd(3, '0')             // "100"
val dropStart = "Dhruw".drop(2)                   // "ruw"
val dropEnd = "Dhruw".dropLast(2)                 // "Dhr"

drulabs

class NEFT: Transaction ... // class NEFT extends Transaction
class IMPS: Transaction ... // class IMPS extends Transaction
class RTGS: Transaction ... // class RTGS extends Transaction

val transaction: Transaction = getCurrentTransaction()

// Now we don't know the type of transaction. It could be either of NEFT, IMPS or RTGS
// So we need to identify the type of trsaction and process it accordingly
when (transaction) {
    is NEFT -> transaction.processNEFT()

drulabs

// Java POJO
public class Person {
    private String name;
    private int age;
    private char gender;

    public Person(String name, int age, char gender) {
        this.name = name;
        this.age = age;
        this.gender = gender;

drulabs

fun main (args: Array<String>) {
    val x = arrayListOf("A.B", "B.C", "C.D", "D.E", "E.F")
    println(x.map { stringStirrer(it) })
    // above line prints [Axx, Bxx, Cxx, Dxx, Exx]
}

fun stringStirrer(param: String): String {
    var changes = param.substringBefore(".")
    changes += "xx"
    return changes

drulabs

import android.content.Context
import android.content.SharedPreferences

private fun doSomething(context: Context) {
    val prefs = context.getSharedPreferences("app_prefs", Context.MODE_PRIVATE).edit()
    prefs.persist(key = "my_name", value = "Kaushal Dhruw")
}

fun SharedPreferences.Editor.persist(key: String, value: String) {
    putString(key, value)

drulabs

import android.database.sqlite.SQLiteDatabase

// Add an extension function to perform SQLite operations
// This is a higher order function as it takes a function as parameter (operation)
// @param operation: a function that takes no parameter and returns nothing
fun SQLiteDatabase.performDBTransaction(operation: () -> Unit) {
    beginTransaction()
    operation() // this is the passed function
    endTransaction()
}

drulabs

// Add a function toINR() to kotlin's Double type
fun Double.toINR() = this * oneDollarInINR
// Yes it is a single line function

val netAmountDeposited = 230.0
                                                 
println("Net amount deposited(in INR): ${netAmountDeposited.toINR()}")
// Did you notice the string interpolation above
                                                 

drulabs

// THE KOTLIN WAY

// 1. Who did maximum number of transactions
val maxTransactionsBy = customers.maxBy { it.transactions.count() }

// List all transactions irrespective of customers
val transactions = customers.flatMap { it.transactions }

// 2a. Get total amount deposited in the bank (use transactions constant from above)
val totalAmountDeposited = transactions.filter { it.type == "deposit" }.sumByDouble { it.amount }

drulabs

// JAVA WAY - Who has minimum balance
Customer minBalanceCustomer = Collections.min(
  customers, (o1, o2) -> (int) (o1.getBalance() - o2.getBalance())
);

drulabs

Bank bank = .... ;
List<Customer> customers = bank.getCustomers(); // Get all bank customers
List<Transaction> = customer.getTransactions(); // Get all transactions by 1 customer
double amount = transaction.getAmount(); // Get transaction amount
String transactionType = transaction.getType(); // Get type of transaction (deposit or withdraw)