From 33613a85afc4b1481367fbe92a17ee59c240250b Mon Sep 17 00:00:00 2001
From: Sven Eisenhauer <sven@sven-eisenhauer.net>
Date: Fri, 10 Nov 2023 15:11:48 +0100
Subject: add new repo

---
 .../hjp5/examples/Listing1019.java                 | 81 ++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 Master/Reference Architectures and Patterns/hjp5/examples/Listing1019.java

(limited to 'Master/Reference Architectures and Patterns/hjp5/examples/Listing1019.java')

diff --git a/Master/Reference Architectures and Patterns/hjp5/examples/Listing1019.java b/Master/Reference Architectures and Patterns/hjp5/examples/Listing1019.java
new file mode 100644
index 0000000..4784334
--- /dev/null
+++ b/Master/Reference Architectures and Patterns/hjp5/examples/Listing1019.java	
@@ -0,0 +1,81 @@
+/* Listing1019.java */
+
+interface Observer
+{
+  public void update(Subject subject);
+}
+
+class Subject
+{
+  Observer[] observers   = new Observer[5];
+  int        observerCnt = 0;
+
+  public void attach(Observer observer)
+  {
+    observers[observerCnt++] = observer;
+  }
+
+  public void detach(Observer observer)
+  {
+    for (int i = 0; i < observerCnt; ++i) {
+      if (observers[i] == observer) {
+        --observerCnt;
+        for (;i < observerCnt; ++i) {
+          observers[i] = observers[i + 1];
+        }
+        break;
+      }
+    }
+  }
+
+  public void fireUpdate()
+  {
+    for (int i = 0; i < observerCnt; ++i) {
+      observers[i].update(this);
+    }
+  }
+}
+
+class Counter
+{
+  int cnt = 0;
+  Subject subject = new Subject();
+
+  public void attach(Observer observer)
+  {
+    subject.attach(observer);
+  }
+
+  public void detach(Observer observer)
+  {
+    subject.detach(observer);
+  }
+
+  public void inc()
+  {
+    if (++cnt % 3 == 0) {
+      subject.fireUpdate();
+    }
+  }
+}
+
+public class Listing1019
+{
+  public static void main(String[] args)
+  {
+    Counter counter = new Counter();
+    counter.attach(
+      new Observer()
+      {
+        public void update(Subject subject)
+        {
+          System.out.print("divisible by 3: ");
+        }
+      }
+    );
+    while (counter.cnt < 10) {
+      counter.inc();
+      System.out.println(counter.cnt);
+    }
+  }
+}
\ No newline at end of file
-- 
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