exercise

Author: meowpunch

src/main/java/behavioral/observer/Exercise.java

@@ -0,0 +1,63 @@
+package behavioral.observer;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.util.HashSet;
+import java.util.Set;
+
+/*
+    Game needs to propagate the change of the total number of rats to each rats
+    Game is Observable/Publisher
+ */
+class Game {
+
+  Set<Rat> rats = new HashSet<>(); // observers
+
+  void addRat(Rat rat) {
+    rats.add(rat);
+    updateRatAttack();
+  }
+
+  void removeRat(Rat rat) {
+    rats.remove(rat);
+    updateRatAttack();
+  }
+
+  void updateRatAttack() {
+    rats.forEach(
+        rat -> rat.attack = rats.size()
+    );
+    System.out.println("update each rat's attack as " + rats.size());
+  }
+}
+
+class Rat implements Closeable // subscription
+{
+
+  private final Game game;
+  public int attack = 1; // keep the total number of rats
+
+  public Rat(Game game) {
+    this.game = game;
+    game.addRat(this); // request
+  }
+
+  @Override
+  public void close() {
+    this.game.removeRat(this); //cancel
+  }
+}
+
+public class Exercise {
+
+  public static void main(String[] args) {
+
+    var game = new Game();
+
+    var r1 = new Rat(game);
+    var r2 = new Rat(game);
+    var r3 = new Rat(game);
+
+    r1.close();
+  }
+}

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

@@ -29,7 +29,7 @@ private static void testObserver(RunnableObservable runnableObservable) {
     Observer ob1 = (o, arg) -> System.out.println(Thread.currentThread().getName() + " ob1 consume " + arg); // override `void update` method
     Observer ob2 = (o, arg) -> System.out.println(Thread.currentThread().getName() + " ob2 consume " + arg);
 
-    runnableObservable.addObserver(ob1);
+    runnableObservable.addObserver(ob1); // subscribe
     runnableObservable.addObserver(ob2);
 
     ExecutorService executorService = Executors.newSingleThreadExecutor();