ingramchen · August 29, 2015 14:04 · Jul 18, 2014 · Jul 18, 2014
diff --git a/gistfile1.java b/gistfile1.java
@@ -14,31 +14,20 @@
 import com.google.common.collect.ImmutableSet;
 
 /**
- * 主要有兩個方法 java7Imperative() 和 java8() ，分別展示 imperative 與 functional 風格的寫法。
+ * 主要有兩個方法 <code>java7_imperative()</code> 和 <code>java8_functional()</code>，分別展示 
+ * imperative 與 functional 風格的寫法。
+ * 
  * 程式的目的在求誰是最多人共有的朋友。
  * 
  * @author ingram
  *
  */
 public class UserTest {
 
-  public static void main(String[] args) {
-    final Friend[] f = { new Friend("a"), new Friend("b"), new Friend("c"), new Friend("d") };
-    final User[] users = new User[6];
-    users[0] = new User(f[0], f[1]);
-    users[1] = new User(f[1], f[2]);
-    users[2] = new User(f[3], f[2]);
-    users[3] = new User(f[0], f[1], f[2], f[3]);
-    users[4] = new User(f[1]);
-    users[5] = new User();
-
-    new UserTest().java7Imperative(asList(users));
-    new UserTest().java8(asList(users));
-  }
-
-  private final UserDao userDao = new UserDao();
-
-  public void java7Imperative(List<User> users) {
+  /**
+   * Java 7 external iteration, 共 21 行。
+   */
+  public void java7_imperative(List<User> users) {
     final Map<Friend, Long> friendCounts = new HashMap<>();
     for (final User user : users) {
       for (final Friend friend : user.getFriends()) {
@@ -62,14 +51,34 @@ public void java7Imperative(List<User> users) {
     }
   }
 
-  public void java8(List<User> users) {
+  /**
+   * Java 8 internal iteration, 共 6 行。
+   */
+  public void java8_functional(List<User> users) {
     users.stream().flatMap(user -> user.getFriends().stream())
          .collect(groupingBy(Function.identity(), summingLong(friend -> 1)))
          .entrySet().stream() // Entry<Friend, Long> friendCount
          .max(Entry.comparingByValue())
          .map(Entry::getKey)
          .ifPresent(userDao::saveMostCommonFriend);
   }
+
+  public static void main(String[] args) {
+    final Friend[] f = { new Friend("a"), new Friend("b"), new Friend("c"), new Friend("d") };
+    final User[] users = new User[6];
+    users[0] = new User(f[0], f[1]);
+    users[1] = new User(f[1], f[2]);
+    users[2] = new User(f[3], f[2]);
+    users[3] = new User(f[0], f[1], f[2], f[3]);
+    users[4] = new User(f[1]);
+    users[5] = new User();
+
+    new UserTest().java7_imperative(asList(users));
+    new UserTest().java8_functional(asList(users));
+  }
+
+  UserDao userDao = new UserDao();
+
 }
 
 class Friend {
@@ -121,4 +130,4 @@ class UserDao {
   public void saveMostCommonFriend(Friend friend) {
     System.out.println("saved: " + friend);
   }
-}
+}
diff --git a/gistfile1.java b/gistfile1.java
@@ -0,0 +1,124 @@
+package com.liquable.nemo.model;
+
+import static java.util.Arrays.asList;
+import static java.util.stream.Collectors.groupingBy;
+import static java.util.stream.Collectors.summingLong;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+import java.util.function.Function;
+
+import com.google.common.collect.ImmutableSet;
+
+/**
+ * 主要有兩個方法 java7Imperative() 和 java8() ，分別展示 imperative 與 functional 風格的寫法。
+ * 程式的目的在求誰是最多人共有的朋友。
+ * 
+ * @author ingram
+ *
+ */
+public class UserTest {
+
+  public static void main(String[] args) {
+    final Friend[] f = { new Friend("a"), new Friend("b"), new Friend("c"), new Friend("d") };
+    final User[] users = new User[6];
+    users[0] = new User(f[0], f[1]);
+    users[1] = new User(f[1], f[2]);
+    users[2] = new User(f[3], f[2]);
+    users[3] = new User(f[0], f[1], f[2], f[3]);
+    users[4] = new User(f[1]);
+    users[5] = new User();
+
+    new UserTest().java7Imperative(asList(users));
+    new UserTest().java8(asList(users));
+  }
+
+  private final UserDao userDao = new UserDao();
+
+  public void java7Imperative(List<User> users) {
+    final Map<Friend, Long> friendCounts = new HashMap<>();
+    for (final User user : users) {
+      for (final Friend friend : user.getFriends()) {
+        if (!friendCounts.containsKey(friend)) {
+          friendCounts.put(friend, 1L);
+        } else {
+          friendCounts.put(friend, friendCounts.get(friend) + 1);
+        }
+      }
+    }
+    Friend topFriend = null;
+    long max = -1;
+    for (final Entry<Friend, Long> entry : friendCounts.entrySet()) {
+      if (entry.getValue() > max) {
+        topFriend = entry.getKey();
+        max = entry.getValue();
+      }
+    }
+    if (topFriend != null) {
+      userDao.saveMostCommonFriend(topFriend);
+    }
+  }
+
+  public void java8(List<User> users) {
+    users.stream().flatMap(user -> user.getFriends().stream())
+         .collect(groupingBy(Function.identity(), summingLong(friend -> 1)))
+         .entrySet().stream() // Entry<Friend, Long> friendCount
+         .max(Entry.comparingByValue())
+         .map(Entry::getKey)
+         .ifPresent(userDao::saveMostCommonFriend);
+  }
+}
+
+class Friend {
+
+  String name;
+
+  Friend(String name) {
+    this.name = name;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) return true;
+    if (obj == null) return false;
+    if (getClass() != obj.getClass()) return false;
+    final Friend other = (Friend) obj;
+    if (name == null) {
+      if (other.name != null) return false;
+    } else if (!name.equals(other.name)) return false;
+    return true;
+  }
+
+  @Override
+  public int hashCode() {
+    return ((name == null) ? 0 : name.hashCode());
+  }
+
+  @Override
+  public String toString() {
+    return name;
+  }
+}
+
+class User {
+
+  Set<Friend> friends;
+
+  User(Friend... friends) {
+    this.friends = ImmutableSet.copyOf(friends);
+  }
+
+  Set<Friend> getFriends() {
+    return friends;
+  }
+}
+
+class UserDao {
+  // ... do database save...
+  public void saveMostCommonFriend(Friend friend) {
+    System.out.println("saved: " + friend);
+  }
+}