KTLN-622: Implement code for the article differentiating Kotlin Any vs * in generics. (#1142)

* KTLN-622: Implement code for the article differentiating Kotlin Any vs * in generics.

* KTLN-622: Implement code for the article differentiating Kotlin Any vs * in generics.

* KTLN-622: Implement code for the article differentiating Kotlin Any vs * in generics.

* KTLN-622: Implement code for the article differentiating Kotlin Any vs * in generics.

* KTLN-622: Implement code for the article differentiating Kotlin Any vs * in generics.

Author: vedarths

core-kotlin-modules/core-kotlin-11/README.md

@@ -1,2 +1,2 @@
 ### Relevant Articles
-- [Convert a Data Class to ByteBuffer in Kotlin](https://www.baeldung.com/kotlin/convert-data-class-to-bytebuffer)
+

core-kotlin-modules/core-kotlin-12/README.md

@@ -0,0 +1,2 @@
+### Relevant Articles
+- Difference between "*" and "Any" in Kotlin generics - Link to be updated

core-kotlin-modules/core-kotlin-12/pom.xml

@@ -0,0 +1,37 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
+         http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-kotlin-12</artifactId>
+    <name>core-kotlin-12</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>core-kotlin-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <build>
+        <sourceDirectory>src/main/kotlin</sourceDirectory>
+        <testSourceDirectory>src/test/kotlin</testSourceDirectory>
+        <plugins>
+            <plugin>
+                <groupId>org.jetbrains.kotlin</groupId>
+                <artifactId>kotlin-maven-plugin</artifactId>
+                <version>${kotlin.version}</version>
+                <executions>
+                    <execution>
+                        <id>compile</id>
+                        <phase>compile</phase>
+                        <goals>
+                            <goal>compile</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+</project>

core-kotlin-modules/core-kotlin-12/src/main/kotlin/com/baeldung/casting/Candy.kt

@@ -0,0 +1,8 @@
+package com.baeldung.casting
+
+sealed class Candy(val name: String) {
+    override fun toString() = name
+}
+
+object ChocolateBar: Candy("Chocolate Bar")
+object Lollipop : Candy("Lollipop")

core-kotlin-modules/core-kotlin-12/src/main/kotlin/com/baeldung/casting/SpookyTrinket.kt

@@ -0,0 +1,7 @@
+package com.baeldung.casting
+
+sealed class SpookyTrinket(val name: String) {
+    override fun toString() = name
+}
+object FakeSpider : SpookyTrinket("Fake Spider")
+object VampireFang : SpookyTrinket("Vampire Fang")

core-kotlin-modules/core-kotlin-12/src/main/kotlin/com/baeldung/casting/TreatDispenser.kt

@@ -0,0 +1,35 @@
+package com.baeldung.casting
+
+import kotlin.collections.MutableList
+import kotlin.collections.mutableListOf
+import kotlin.collections.firstOrNull
+
+class TreatDispenser<T>(private val treats: MutableList<T> = mutableListOf()) {
+
+    // Dispense the first treat
+    fun dispenseTreat(): T? {
+        return if (treats.isNotEmpty()) treats.removeFirst() else null
+    }
+
+    // Peek at the next treat without removing it
+    fun peekNextTreat(): T? {
+        return treats.firstOrNull()
+    }
+
+    // Add a treat to the dispenser
+    fun addTreat(treat: T) {
+        treats.add(treat)
+    }
+}
+
+// Function using * (Star Projection)
+fun peekAtNextTreat(dispenser: TreatDispenser<*>) {
+    val nextTreat = dispenser.peekNextTreat()
+    println("The next treat is: $nextTreat")
+}
+
+// Function using Any (restricted to non-nullable types)
+fun peekAtNextTreatAny(dispenser: TreatDispenser<Any>) {
+    val nextTreat = dispenser.peekNextTreat()
+    println("The next treat is: $nextTreat")
+}

core-kotlin-modules/core-kotlin-12/src/test/kotlin/com/baeldung/casting/TreatDispenserUnitTest.kt

@@ -0,0 +1,65 @@
+package com.baeldung.casting
+
+import org.junit.Test
+import org.junit.jupiter.api.Assertions.*
+
+class TreatDispenserUnitTest {
+
+    @Test
+    fun `dispenseTreat should return the first treat`() {
+
+        val dispenser = TreatDispenser<Candy>()
+        dispenser.addTreat(ChocolateBar)
+        dispenser.addTreat(Lollipop)
+
+        assertEquals(ChocolateBar, dispenser.dispenseTreat())
+        assertEquals(Lollipop, dispenser.dispenseTreat())
+        assertNull(dispenser.dispenseTreat())
+    }
+
+    @Test
+    fun `peekNextTreat should show the next treat without removing it`() {
+        val dispenser = TreatDispenser<Candy>()
+        dispenser.addTreat(Lollipop)
+
+        assertEquals(Lollipop, dispenser.peekNextTreat())
+        assertEquals(Lollipop, dispenser.peekNextTreat())
+    }
+
+    @Test
+    fun `peekAtNextTreat using star projection works for all types`() {
+        val candyDispenser = TreatDispenser<Candy>()
+        candyDispenser.addTreat(ChocolateBar)
+
+        val trinketDispenser = TreatDispenser<SpookyTrinket>()
+        trinketDispenser.addTreat(VampireFang)
+        trinketDispenser.addTreat(FakeSpider)
+
+        // Test with Candy dispenser
+        assertDoesNotThrow {
+            peekAtNextTreat(candyDispenser)
+        }
+
+        // Test with Trinket dispenser
+        assertDoesNotThrow {
+            peekAtNextTreat(trinketDispenser)
+        }
+    }
+
+    @Test
+    fun `peekAtNextTreatAny fails for non-Any dispensers`() {
+        val candyDispenser = TreatDispenser<Candy>()
+        candyDispenser.addTreat(ChocolateBar)
+
+        // This would fail type checking, hence commented:
+        // peekAtNextTreatAny(candyDispenser) // Error: Type mismatch
+
+        val anyDispenser = TreatDispenser<Any>()
+        anyDispenser.addTreat("Surprise Treat")
+
+        assertDoesNotThrow {
+            peekAtNextTreatAny(anyDispenser)
+        }
+    }
+
+}

core-kotlin-modules/pom.xml

@@ -25,6 +25,7 @@
         <module>core-kotlin-9</module>
         <module>core-kotlin-10</module>
         <module>core-kotlin-11</module>
+        <module>core-kotlin-12</module>
         <module>core-kotlin-advanced</module>
         <module>core-kotlin-advanced-2</module>
         <module>core-kotlin-advanced-3</module>