mtorchiano · April 23, 2018 11:33 · Apr 23, 2018
diff --git a/_README.md b/_README.md
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+## Replacing Observer-Observable (inheritance vs. composition)
+
+Since Java 9 the pair Observer-Observable have been declared `deprecated`.
+
+
+    They don't provide a rich enough event model for applications. 
+    For example, they support only the notion that something has changed, 
+    but they don't convey any information about what has changed. 
+    There are also some thread-safety and sequencing issues that cannot be fixed compatibly. 
+
+    [...]
+
+    Observable has fallen into disuse and is no longer under active development.
+
+Personally I used to show the  Observer-Observable in classroom to provide an example
+of how interfaces can be used for *callback-like* behavior.
+
+The *deprecation* forced me to look into the alternatives suggested. 
+The Bean event model is quite general and can be adatped to the same use cases intended for the pair.
+
+In addition comparing the two solutions we can observe two ditinct approaches to reused: inheritance vs. composition.
diff --git a/beans.Concerned.java b/beans.Concerned.java
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+package observer.beans;
+
+import java.beans.PropertyChangeEvent;
+import java.beans.PropertyChangeListener;
+
+public class Concerned implements PropertyChangeListener {
+
+	@Override
+	public void propertyChange(PropertyChangeEvent evt) {
+		System.out.println("Variation of " + evt.getPropertyName());
+		System.out.println("\t(" + evt.getOldValue() + 
+							" -> " + evt.getNewValue() + ")");
+		System.out.println("Property in object " + evt.getSource());
+	}
+
+}
diff --git a/beans.Subject.java b/beans.Subject.java
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+package observer.beans;
+
+import java.beans.PropertyChangeListener;
+import java.beans.PropertyChangeSupport;
+
+public class Subject {
+
+	String property="initial";
+	// contain a support object instead of extending the support class
+	PropertyChangeSupport pcs = new  PropertyChangeSupport(this);
+
+	public void addObserver(PropertyChangeListener l) {
+		pcs.addPropertyChangeListener("theProperty", l);
+	}
+
+	public void setProperty(String val) {
+		String old = property;
+		property = val;
+		pcs.firePropertyChange("theProperty", old, val);
+	}
+
+	public String toString() { return "The subject object"; };
+}
diff --git a/main.java b/main.java
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+public class EsObserver {
+
+	public static void main(String[] args) {
+
+		Subject s = new Subject();
+
+		Concerned o = new Concerned();
+
+		s.addObserver(o);
+
+		s.setProperty("new");
+
+	}
+
+}
diff --git a/oo.Concerned.java b/oo.Concerned.java
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+package observer.oo;
+
+import java.util.Observable;
+import java.util.Observer;
+
+public class Concerned implements Observer {
+
+	@Override
+	public void update(Observable src, Object arg) {
+		System.out.println("Variation of " + arg);
+		System.out.println("Property in object " + src);
+	}
+
+}
diff --git a/oo.Subject.java b/oo.Subject.java
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+package observer.oo;
+
+import java.util.Observable;
+
+public class Subject extends Observable {
+
+	String property="initial";
+
+	public void setProperty(String val) {
+		property = val;
+		setChanged();
+		notifyObservers("theProperty");
+	}
+
+	public String toString() { return "The subject object"; };
+}
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