Iterator design pattern - AFTER CODE for Face book friends project

premaseem · premaseem · commit e96236fe301e · 2018-03-04T17:45:53.000-06:00
- Provides limited control over data access
diff --git a/pattern/src/com/premaseem/Client.java b/pattern/src/com/premaseem/Client.java
@@ -1,7 +1,5 @@
 package com.premaseem;
 
-import java.util.List;
-
 /*
 @author: Aseem Jain
 @title: Design Patterns with Java 9
@@ -12,7 +10,23 @@ public static void main (String[] args) {
         System.out.println("Iterator Pattern BEFORE CODE");
 
         FaceBook faceBook = new FaceBook();
+        Iterator faceBookIterator = faceBook.getIterator();
+
+        // Loop over
+        // init data with first(), keep increment with next()
+        // and check termination condition with hasNext()
+        for(faceBookIterator.first();faceBookIterator.hasNext();faceBookIterator.next()){
+            System.out.println(faceBookIterator.currentValue());
+        }
+
+        // $$$ Lesson Learned $$$
+        // Loose coupling no need to know or import data structure
+        // Data cannot be compromised ;-)
+        // Provides limited control over data access
 
+
+
+        /* OLD CODE
         // Data structure is exposed
         List<String> friendsList = faceBook.getFriendsList();
 
@@ -36,7 +50,7 @@ public static void main (String[] args) {
         for (int i = 0; i < friendsList.size(); i++) {
             System.out.println(friendsList.get(i));
         }
-
+*/
         // Lesson Learned
         // 1. Underlying Data structure is exposed
         // 2. Data can be manipulated
diff --git a/pattern/src/com/premaseem/FaceBook.java b/pattern/src/com/premaseem/FaceBook.java
@@ -2,6 +2,7 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.NoSuchElementException;
 
 /*
 @author: Aseem Jain
@@ -20,7 +21,42 @@ public FaceBook () {
         friendsList.add("Super Man");
     }
 
-    public List<String> getFriendsList () {
-        return friendsList;
+//    public List<String> getFriendsList () {
+//        return friendsList;
+//    }
+
+    public Iterator getIterator() {
+        return new Iterator(this);
     }
 }
+
+class Iterator {
+    private FaceBook faceBook;
+    private java.util.Iterator iterator;
+    private String value;
+
+    public Iterator(FaceBook faceBook) {
+        this.faceBook = faceBook;
+    }
+
+    public void first() {
+        iterator = faceBook.friendsList.iterator();
+        next();
+    }
+
+    public void next() {
+        try {
+            value = (String)iterator.next();
+        } catch (NoSuchElementException ex) {
+            value =  null;
+        }
+    }
+
+    public boolean hasNext() {
+        return value != null;
+    }
+
+    public String currentValue() {
+        return value;
+    }
+}
