Converted code to kotlin

kotlin/src/main/kotlin/Invoice.kt

@@ -0,0 +1 @@
+data class Invoice(val customer: String, val performances: List<Performance>)

kotlin/src/main/kotlin/Performance.kt

@@ -0,0 +1 @@
+data class Performance(val playID: String, val audience: Int)

kotlin/src/main/kotlin/Play.kt

@@ -0,0 +1 @@
+data class Play(val name: String, val type: String)

kotlin/src/main/kotlin/StatementPrinter.kt

@@ -0,0 +1,51 @@
+import java.text.NumberFormat
+import java.util.Locale
+import kotlin.math.floor
+import kotlin.math.max
+
+class StatementPrinter {
+
+    fun print(invoice: Invoice, plays: Map<String, Play>): String {
+        var totalAmount = 0
+        var volumeCredits = 0
+        var result = "Statement for ${invoice.customer}\n"
+
+        val frmt = NumberFormat.getCurrencyInstance(Locale.US)
+
+        for ((playID, audience) in invoice.performances) {
+            val play = plays[playID]
+            var thisAmount = 0
+
+            when (play?.type) {
+                "tragedy" -> {
+                    thisAmount = 40000
+                    if (audience > 30) {
+                        thisAmount += 1000 * (audience - 30)
+                    }
+                }
+                "comedy" -> {
+                    thisAmount = 30000
+                    if (audience > 20) {
+                        thisAmount += 10000 + 500 * (audience - 20)
+                    }
+                    thisAmount += 300 * audience
+                }
+                else -> throw Error("unknown type: {play.type}")
+            }
+
+            // add volume credits
+            volumeCredits += max(audience - 30, 0)
+            // add extra credit for every ten comedy attendees
+            if ("comedy" == play.type) volumeCredits += floor((audience / 5).toDouble()).toInt()
+
+            // print line for this order
+            result += "  ${play.name}: ${frmt.format((thisAmount / 100).toLong())} ($audience seats)\n"
+
+            totalAmount += thisAmount
+        }
+        result += "Amount owed is ${frmt.format((totalAmount / 100).toLong())}\n"
+        result += "You earned $volumeCredits credits\n"
+        return result
+    }
+
+}

kotlin/src/test/kotlin/StatementPrinterTests.kt

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+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertThrows
+import org.junit.jupiter.api.Test
+
+class StatementPrinterTests {
+
+    @Test
+    internal fun exampleStatement() {
+        val expected = "Statement for BigCo\n" +
+                "  Hamlet: \$650.00 (55 seats)\n" +
+                "  As You Like It: \$580.00 (35 seats)\n" +
+                "  Othello: \$500.00 (40 seats)\n" +
+                "Amount owed is \$1,730.00\n" +
+                "You earned 47 credits\n"
+
+        val plays = mapOf(
+            "hamlet" to Play("Hamlet", "tragedy"),
+            "as-like" to Play("As You Like It", "comedy"),
+            "othello" to Play("Othello", "tragedy")
+        )
+
+        val invoice = Invoice(
+            "BigCo", listOf(
+                Performance("hamlet", 55),
+                Performance("as-like", 35),
+                Performance("othello", 40)
+            )
+        )
+
+        val statementPrinter = StatementPrinter()
+        val result = statementPrinter.print(invoice, plays)
+
+        assertEquals(expected, result)
+    }
+
+    @Test
+    internal fun statementWithNewPlayTypes() {
+        val plays = mapOf(
+            "henry-v" to Play("Henry V", "history"),
+            "as-like" to Play("As You Like It", "pastoral")
+        )
+
+        val invoice = Invoice(
+            "BigCo", listOf(
+                Performance("henry-v", 53),
+                Performance("as-like", 55)
+            )
+        )
+
+        val statementPrinter = StatementPrinter()
+        assertThrows(Error::class.java) { statementPrinter.print(invoice, plays) }
+    }
+}