observer

Author: code4craft

src/main/java/helloworld/Main.java

@@ -11,6 +11,8 @@
 import helloworld.behavioral.mediator.HelloWorldSlogan;
 import helloworld.behavioral.mediator.HelloWorldTarget;
 import helloworld.behavioral.memento.HelloWorldMementoOriginator;
+import helloworld.behavioral.observer.HelloWorldObserver;
+import helloworld.behavioral.observer.Subject;
 import helloworld.creational.abstract_factory.AbstractFactory;
 import helloworld.creational.abstract_factory.SplitHelloWorldFactory;
 import helloworld.creational.builder.HelloWorldBuilder;
@@ -114,5 +116,8 @@ public static void main(String[] args) throws InstantiationException, IllegalAcc
         helloWorldMementoOriginator.restoreFromMemento(memento);
         System.out.println(helloWorldMementoOriginator.helloWorld());
 
+        Subject subject = new Subject().attach(new HelloWorldObserver());
+        subject.notifyObservers();
+
     }
 }

src/main/java/helloworld/behavioral/observer/HelloWorldObserver.java

@@ -0,0 +1,20 @@
+package helloworld.behavioral.observer;
+
+import java.io.PrintStream;
+
+/**
+ * @author yihua.huang@dianping.com
+ */
+public class HelloWorldObserver implements Observer{
+
+    private PrintStream printer = System.out;
+
+    public void setPrinter(PrintStream printer) {
+        this.printer = printer;
+    }
+
+    @Override
+    public void update() {
+        printer.println("Hello Observer!");
+    }
+}

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

@@ -0,0 +1,9 @@
+package helloworld.behavioral.observer;
+
+/**
+ * @author yihua.huang@dianping.com
+ */
+public interface Observer {
+
+    public void update();
+}

src/main/java/helloworld/behavioral/observer/Subject.java

@@ -0,0 +1,29 @@
+package helloworld.behavioral.observer;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * @author yihua.huang@dianping.com
+ */
+public class Subject {
+
+    private List<Observer> observers;
+
+    public Subject() {
+        this.observers = new LinkedList<Observer>();
+    }
+
+    public Subject attach(Observer observer){
+        observers.add(observer);
+        return this;
+    }
+
+    public void notifyObservers(){
+        for (Observer observer : observers) {
+            observer.update();
+        }
+    }
+
+}

src/test/java/helloworld/behavioral/observer/HelloWorldObserverTest.java

@@ -0,0 +1,23 @@
+package helloworld.behavioral.observer;
+
+import org.junit.Test;
+
+import java.io.PrintStream;
+
+import static org.mockito.Mockito.*;
+
+/**
+ * @author yihua.huang@dianping.com
+ */
+public class HelloWorldObserverTest {
+
+    @Test
+    public void testHelloWorldObserver(){
+        HelloWorldObserver observer = new HelloWorldObserver();
+        PrintStream mockPrinter = mock(PrintStream.class);
+        observer.setPrinter(mockPrinter);
+        Subject subject = new Subject().attach(observer);
+        subject.notifyObservers();
+        verify(mockPrinter,times(1)).println("Hello Observer!");
+    }
+}