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Commit 1778d54

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added Proxy pattern
1 parent d7e868b commit 1778d54

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package design_patterns
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/**
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*
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* Proxy is a structural design pattern that provides an object
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*
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* that controls access to another object by intercepting all calls.
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*
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* There are several types of this pattern:
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*
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* 1) Logging proxy - saves all calls to a real object with their parameters to the log (shown in this example)
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* 2) Remote proxy - provides communication with an object which is located in a different address space or on a remote machine (Java Remote Procedure Call)
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* 3) Virtual proxy - ensures that a real object is created only when it is actually needed (shown in this example)
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* 4) Protection proxy - checks whether the caller has the necessary rights to execute the request
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* 5) Caching proxy - provides temporary storage of calculation results
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* 6) Synchronizing proxy - performs synchronized access control to an object in a multi-threaded environment (Collections.synchronized** methods)
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* 7) Smart reference proxy - performs additional actions when a link is created to an object
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*
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*/
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interface AudioPlayer {
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val currentState: String
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fun play(audio: String)
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fun pause()
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fun resume()
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fun stop()
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}
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// we have the simple player simulation
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class AudioPlayerImpl : AudioPlayer {
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private var currentAudio: String = ""
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private var currentStatus = MediaPlayerStatus.NOT_INITIALIZED
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override val currentState: String
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get() = """
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current audio: $currentAudio
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current status: $currentStatus
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""".trimIndent()
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override fun play(audio: String) {
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if (audio.isNotBlank()) {
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currentAudio = audio
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currentStatus = MediaPlayerStatus.RUNNING
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}
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}
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override fun pause() {
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if (currentStatus == MediaPlayerStatus.RUNNING) {
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currentStatus = MediaPlayerStatus.PAUSED
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}
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}
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override fun resume() {
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if (currentStatus == MediaPlayerStatus.PAUSED) {
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currentStatus = MediaPlayerStatus.RUNNING
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}
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}
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override fun stop() {
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if (currentStatus != MediaPlayerStatus.NOT_INITIALIZED) {
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currentAudio = ""
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currentStatus = MediaPlayerStatus.NOT_INITIALIZED
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}
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}
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enum class MediaPlayerStatus {
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NOT_INITIALIZED, PAUSED, RUNNING
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}
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}
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// MediaPlayerProxy defers the creation of a real object (virtual proxy) and logs all its calls (logging proxy)
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class AudioPlayerProxy : AudioPlayer {
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// deferred creation of the real player
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private val player: AudioPlayer by lazy { AudioPlayerImpl() }
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override val currentState: String
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get() = player.currentState
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override fun play(audio: String) {
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player.play(audio)
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// logs real player calls
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println("play audio: $audio")
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}
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override fun pause() {
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player.pause()
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println("pause")
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}
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override fun resume() {
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player.resume()
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println("resume")
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}
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override fun stop() {
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player.stop()
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println("stop")
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}
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}
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package design_patterns
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import org.junit.Test
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import org.junit.Assert.assertEquals
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class ProxyTest {
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@Test
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fun test() {
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// we use the proxy object instead of a real one
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val mediaPlayer = AudioPlayerProxy()
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mediaPlayer.play("track_0.mp3")
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assertEquals("""
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current audio: track_0.mp3
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current status: RUNNING
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""".trimIndent(), mediaPlayer.currentState)
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mediaPlayer.pause()
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assertEquals("""
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current audio: track_0.mp3
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current status: PAUSED
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""".trimIndent(), mediaPlayer.currentState)
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mediaPlayer.resume()
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assertEquals("""
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current audio: track_0.mp3
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current status: RUNNING
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""".trimIndent(), mediaPlayer.currentState)
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mediaPlayer.stop()
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assertEquals("""
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current audio:
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current status: NOT_INITIALIZED
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""".trimIndent(), mediaPlayer.currentState)
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}
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}

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