custom observer pattern

Author: meowpunch

src/main/java/behavioral/observer/Observable.java

@@ -0,0 +1,26 @@
+package behavioral.observer;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class Observable<T> {
+
+  private final List<Observer<T>> subscribedObservers = new ArrayList<>();
+
+  public void subscribe(Observer<T> observer) {
+    subscribedObservers.add(observer);
+  }
+
+  @SafeVarargs
+  public final void subscribe(Observer<T>... observers) {
+    subscribedObservers.addAll(Arrays.asList(observers));
+  }
+
+  protected void propertyChanged(T source, String propertyName, Object newValue) {
+    subscribedObservers
+        .forEach(
+            observer -> observer.handle(new PropertyChangeEventArgs<>(source, propertyName, newValue))
+        );
+  }
+}

src/main/java/behavioral/observer/Observer.java

@@ -0,0 +1,5 @@
+package behavioral.observer;
+
+interface Observer<T> {
+  void handle(PropertyChangeEventArgs<T> args);
+}

src/main/java/behavioral/observer/ObserverPatternApp.java

@@ -0,0 +1,18 @@
+package behavioral.observer;
+
+public class ObserverPatternApp {
+
+  public static void main(String[] args) {
+
+    Observer<Person> ob1 = p -> System.out.println("ob1 consume " + p.source());
+    Observer<Person> ob2 = p -> System.out.println("ob2 consume " + p.source());
+
+    Person p = new Person("Jinhoon", 29);
+
+    p.subscribe(ob1, ob2);
+
+    p.setAge(30);
+    p.setAge(31);
+  }
+
+}

src/main/java/behavioral/observer/Person.java

@@ -0,0 +1,18 @@
+package behavioral.observer;
+
+import lombok.AllArgsConstructor;
+import lombok.ToString;
+
+@ToString
+@AllArgsConstructor
+class Person extends Observable<Person>{
+  private final String name;
+  private int age;
+
+  public void setAge(int age) {
+    if (this.age != age) {
+      this.age = age;
+      propertyChanged(this, "age", age);
+    }
+  }
+}

src/main/java/behavioral/observer/PropertyChangeEventArgs.java

@@ -0,0 +1,3 @@
+package behavioral.observer;
+
+record PropertyChangeEventArgs<T> (T source, String propertyName, Object newValue) {}

src/main/java/concurrency/reactive/Ob.java

@@ -70,8 +70,8 @@ public void run() {
   @AllArgsConstructor
   static class Person extends RunnableObservable {
 
-    String name;
-    int age;
+    private final String name;
+    private int age;
 
     void setAge(int newAge) {
       if (this.age != newAge) {