KTLN-603: The Composite Pattern in Kotlin (#853)

* added code

* made code fixes

Author: nappy29

core-kotlin-modules/core-kotlin-design-patterns/src/main/kotlin/com/baeldung/composite/Movie.kt

@@ -0,0 +1,11 @@
+package com.baeldung.composite
+
+class Movie(private val name: String) : MovieComponent {
+    override fun play(): String {
+        return "Playing movie: $name\n"
+    }
+
+    override fun stop(): String {
+        return "Stopping movie: $name\n"
+    }
+}

core-kotlin-modules/core-kotlin-design-patterns/src/main/kotlin/com/baeldung/composite/MovieComponent.kt

@@ -0,0 +1,6 @@
+package com.baeldung.composite
+
+interface MovieComponent {
+    fun play(): String
+    fun stop(): String
+}

core-kotlin-modules/core-kotlin-design-patterns/src/main/kotlin/com/baeldung/composite/Playlist.kt

@@ -0,0 +1,31 @@
+package com.baeldung.composite
+
+class Playlist(private val name: String) : MovieComponent {
+    private val movieComponents = mutableListOf<MovieComponent>()
+
+    fun add(movieComponent: MovieComponent) {
+        movieComponents.add(movieComponent)
+    }
+
+    fun remove(movieComponent: MovieComponent) {
+        movieComponents.remove(movieComponent)
+    }
+
+    override fun play(): String {
+        val result = StringBuilder()
+        result.append("Playing playlist: $name\n")
+        for (movieComponent in movieComponents) {
+            result.append(movieComponent.play())
+        }
+        return result.toString()
+    }
+
+    override fun stop(): String {
+        val result = StringBuilder()
+        result.append("Stopping playlist: $name\n")
+        for (movieComponent in movieComponents) {
+            result.append(movieComponent.stop())
+        }
+        return result.toString()
+    }
+}

core-kotlin-modules/core-kotlin-design-patterns/src/main/kotlin/com/baeldung/composite/PlaylistComponentClient.kt

@@ -0,0 +1,22 @@
+package com.baeldung.composite
+
+
+fun main() {
+
+    val actionMoviesPlayList = Playlist("Action Movies")
+    actionMoviesPlayList.add(Movie("The Matrix"))
+    actionMoviesPlayList.add(Movie("Die Hard"))
+
+    val comicMoviesPlayList = Playlist("Comic Movies")
+    comicMoviesPlayList.add(Movie("The Hangover"))
+    comicMoviesPlayList.add(Movie("Bridesmaids"))
+
+    val allPlaylists = Playlist("All Playlists")
+    allPlaylists.add(actionMoviesPlayList)
+    allPlaylists.add(comicMoviesPlayList)
+
+    val playResult = allPlaylists.play()
+
+    val stopResult = allPlaylists.stop()
+
+}

core-kotlin-modules/core-kotlin-design-patterns/src/test/kotlin/com/baeldung/composite/MovieApplicationUnitTest.kt

@@ -0,0 +1,57 @@
+package com.baeldung.composite
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+class MovieApplicationUnitTest {
+
+    @Test
+    fun `should play movie`() {
+        val movie = Movie("The Matrix")
+        val result = movie.play()
+
+        assertEquals("Playing movie: The Matrix\n", result)
+    }
+
+    @Test
+    fun `should stop movie`() {
+        val movie = Movie("Die Hard")
+        val result = movie.stop()
+
+        assertEquals("Stopping movie: Die Hard\n", result)
+    }
+
+    @Test
+    fun `should play and stop playlist`() {
+        val actionMoviesPlayList = Playlist("Action Movies")
+        actionMoviesPlayList.add(Movie("The Matrix"))
+        actionMoviesPlayList.add(Movie("Die Hard"))
+
+        val comicMoviesPlayList = Playlist("Comic Movies")
+        comicMoviesPlayList.add(Movie("The Hangover"))
+        comicMoviesPlayList.add(Movie("Bridesmaids"))
+
+        val allPlaylists = Playlist("All Playlists")
+        allPlaylists.add(actionMoviesPlayList)
+        allPlaylists.add(comicMoviesPlayList)
+
+        val playResult = allPlaylists.play()
+        val stopResult = allPlaylists.stop()
+
+        assertEquals("Playing playlist: All Playlists\n" +
+                "Playing playlist: Action Movies\n" +
+                "Playing movie: The Matrix\n" +
+                "Playing movie: Die Hard\n" +
+                "Playing playlist: Comic Movies\n" +
+                "Playing movie: The Hangover\n" +
+                "Playing movie: Bridesmaids\n", playResult)
+
+        assertEquals("Stopping playlist: All Playlists\n" +
+                "Stopping playlist: Action Movies\n" +
+                "Stopping movie: The Matrix\n" +
+                "Stopping movie: Die Hard\n" +
+                "Stopping playlist: Comic Movies\n" +
+                "Stopping movie: The Hangover\n" +
+                "Stopping movie: Bridesmaids\n", stopResult)
+    }
+}