Merge pull request #9551 from MajewskiKrzysztof/KTLN-137

KTLN-137

patterns/design-patterns-behavioral-2/src/main/java/com/baeldung/observer/IObservable.kt

@@ -0,0 +1,18 @@
+package com.baeldung.observer
+
+import java.util.ArrayList
+
+interface IObservable {
+    val observers: ArrayList<IObserver>
+    fun add(observer: IObserver) {
+        observers.add(observer)
+    }
+
+    fun remove(observer: IObserver) {
+        observers.remove(observer)
+    }
+
+    fun sendUpdateEvent() {
+        observers.forEach { it.update() }
+    }
+}

patterns/design-patterns-behavioral-2/src/main/java/com/baeldung/observer/IObserver.kt

@@ -0,0 +1,5 @@
+package com.baeldung.observer
+
+interface IObserver {
+    fun update()
+}

patterns/design-patterns-behavioral-2/src/main/java/com/baeldung/observer/delegates/BaeldungNewsletter.kt

@@ -0,0 +1,10 @@
+package com.baeldung.observer.delegates
+
+import kotlin.properties.Delegates
+
+class BaeldungNewsletter {
+    val newestArticleObservers = mutableListOf<(String) -> Unit>()
+    var newestArticleUrl: String by Delegates.observable("") { _, _, newValue ->
+        newestArticleObservers.forEach { it(newValue) }
+    }
+}

patterns/design-patterns-behavioral-2/src/main/java/com/baeldung/observer/delegates/BaeldungReader.kt

@@ -0,0 +1,8 @@
+package com.baeldung.observer.delegates
+
+fun main() {
+    val newsletter = BaeldungNewsletter()
+    newsletter.newestArticleObservers.add { newestArticleUrl ->
+        println("New Baeldung article: ${newestArticleUrl}")
+    }
+}

patterns/design-patterns-behavioral-2/src/main/java/com/baeldung/observer/standard/BaeldungNewsletter.kt

@@ -0,0 +1,14 @@
+package com.baeldung.observer.standard
+
+import com.baeldung.observer.IObservable
+import com.baeldung.observer.IObserver
+import java.util.ArrayList
+
+class BaeldungNewsletter : IObservable {
+    override val observers: ArrayList<IObserver> = ArrayList()
+    var newestArticleUrl = ""
+        set(value) {
+            field = value
+            sendUpdateEvent()
+        }
+}

patterns/design-patterns-behavioral-2/src/main/java/com/baeldung/observer/standard/BaeldungReader.kt

@@ -0,0 +1,9 @@
+package com.baeldung.observer.standard
+
+import com.baeldung.observer.IObserver
+
+class BaeldungReader(private var newsletter: BaeldungNewsletter) : IObserver {
+    override fun update() {
+        println("New Baeldung article: ${newsletter.newestArticleUrl}")
+    }
+}