1. ////////////////////////////////////////////////////////////////////////////////
2. package pl.glx.pattern;
3.  
4. public interface HasFriendship<Owner extends HasFriendship<Owner, Friend>, Friend extends HasFriendship<Friend, Owner>> {
5.     Friendship<Owner, ?> friendship(Class friendClass);
6. }
7.  
8. ////////////////////////////////////////////////////////////////////////////////
9. package pl.glx.pattern;
10.  
11. public class Friendship<Owner extends HasFriendship, Friend extends HasFriendship>
12.     implements HasFriend<Owner, Friend> {
13.  
14.     final Owner         owner;
15.     Friend              friend;
16.     final Class<Friend> friendClass;
17.     final Class<Owner>  ownerClass;
18.  
19.     public Friendship(Owner owner, Class<Friend> friendClass) {
20.         this.owner = owner;
21.         this.friendClass = friendClass;
22.         this.ownerClass = (Class<Owner>) owner.getClass();
23.     }
24.  
25.     @Override
26.     public Owner set(Friend newFriend) {
27.         if (null != newFriend) {
28.             if (null != newFriend.friendship(ownerClass).friend)
29.                 newFriend.friendship(ownerClass).friend.friendship(friendClass).friend = null;
30.             if (null != this.friend)
31.                 this.friend.friendship(ownerClass).friend = null;
32.             newFriend.friendship(ownerClass).friend = owner;
33.             this.friend = newFriend;
34.         }
35.         else if (null == newFriend) {
36.             if (null != this.friend)
37.                 this.friend.friendship(ownerClass).friend = null;
38.             this.friend = null;
39.         }
40.         return owner;
41.     }
42.  
43.     public Friend get() {
44.         return friend;
45.     }
46. }
47.  
48. ////////////////////////////////////////////////////////////////////////////////
49. package pl.glx.pattern;
50.  
51. import lombok.*;
52. import lombok.experimental.Accessors;
53.  
54. @Accessors(fluent = true)
55. public class A implements HasName<A>, HasFriendship {
56.  
57.     @Getter @Setter
58.     String name;
59.  
60.     public A(String name) {
61.         this.name = name;
62.     }
63.  
64.     Friendship<A, B> fb = new Friendship<>(this, B.class);
65.  
66.     @Override
67.     public Friendship<A, B> friendship(Class friendClass) {
68.         return fb;
69.     }
70. }
71.  
72. ////////////////////////////////////////////////////////////////////////////////
73. package pl.glx.pattern;
74.  
75. import lombok.*;
76. import lombok.experimental.Accessors;
77.  
78. @Accessors(fluent = true)
79. public class B implements HasName<B>, HasFriendship {
80.  
81.     @Getter @Setter
82.     String name;
83.  
84.     public B(String name) {
85.         this.name = name;
86.     }
87.  
88.     Friendship<B, A> fa = new Friendship<>(this, A.class);
89.  
90.     @Override
91.     public Friendship<B, A> friendship(Class friendClass) {
92.         if (friendClass.isAssignableFrom(A.class))
93.             return fa;
94.         return null;
95.     }
96. }
97.  
98. ////////////////////////////////////////////////////////////////////////////////
99. package pl.glx.pattern;
100.  
101. import lombok.experimental.Accessors;
102.  
103. @Accessors(fluent = true)
104. public class Camera implements HasFriendship {
105.  
106.     public final Friendship<Camera, Controller> controller =
107.         new Friendship<>(this, Controller.class);
108.  
109.     @Override
110.     public Friendship<Camera, Controller> friendship(Class cClass) {
111.         return controller;
112.     }
113. }
114.  
115. ////////////////////////////////////////////////////////////////////////////////
116. package pl.glx.pattern;
117.  
118. import lombok.experimental.Accessors;
119.  
120. @Accessors(fluent = true)
121. public class Controller implements HasFriendship {
122.  
123.     public final Friendship<Controller, Camera> camera = new Friendship<>(this, Camera.class);
124.  
125.     public final Friendship<Controller, Mouse>  mouse  = new Friendship<>(this, Mouse.class);
126.  
127.     public Friendship<Controller, ?> friendship(Class friendClass) {
128.         if (friendClass.isAssignableFrom(Mouse.class))
129.             return mouse;
130.         if (friendClass.isAssignableFrom(Camera.class))
131.             return camera;
132.         return null;
133.     }
134. }
135.  
136. ////////////////////////////////////////////////////////////////////////////////
137. package pl.glx.pattern;
138.  
139. import lombok.experimental.Accessors;
140.  
141.  
142. @Accessors(fluent = true)
143. public class Mouse implements HasFriendship {
144.  
145.     public final Friendship<Mouse, Controller> controller = new Friendship<>(this, Controller.class);
146.  
147.     @Override
148.     public Friendship<Mouse, ?> friendship(Class friendClass) {
149.         return controller;
150.     }
151. }
152.  
153. ////////////////////////////////////////////////////////////////////////////////
154. package pl.glx.pattern;
155.  
156. import static pl.glx.common.Helpers.*;
157. import static pl.glx.common.Constants.*;
158.  
159.  
160. public class AB {
161.  
162.     static
163.     private void showObjects(String what, A a1, B b1, A a2, B b2) {
164.  
165.         println(charRepeat('-', 20) + SPACE + what);
166.  
167.         printf("a1 b: %s", null != a1.fb.get() ? a1.fb.get().name() : null);
168.         printf("b1 a: %s", null != b1.fa.get() ? b1.fa.get().name() : null);
169.         printf("a2 b: %s", null != a2.fb.get() ? a2.fb.get().name() : null);
170.         printf("b2 a: %s", null != b2.fa.get() ? b2.fa.get().name() : null);
171.     }
172.  
173.     public static void main(String[] args) {
174.         A a1 = new A("a1");
175.         B b1 = new B("b1");
176.         A a2 = new A("a2");
177.         B b2 = new B("b2");
178.  
179.         a1.fb.set(b1);
180.         b2.fa.set(a2);
181.         showObjects("a1.fb.set(b1); b2.fa.set(a2);", a1, b1, a2, b2);
182.  
183.         a1.fb.set(b2);
184.         showObjects("a1.fb.set(b2);", a1, b1, a2, b2);
185.  
186.         b2.fa.set(a2);
187.         showObjects("b2.fa.set(a2);", a1, b1, a2, b2);
188.  
189.         b1.fa.set(null);
190.         showObjects("b1.fa.set(null);", a1, b1, a2, b2);
191.  
192.         a2.fb.set(null);
193.         showObjects("a2.fb.set(null);", a1, b1, a2, b2);
194.  
195.         Camera cam = new Camera();
196.         Controller ctrl = new Controller();
197.         Mouse mice = new Mouse();
198.  
199.         cam.controller.set(ctrl);
200.         ctrl.mouse.set(mice);
201.         assert cam == ctrl.camera.get() : "cam != ctrl.camera.get()";
202.         assert ctrl == cam.controller.get() : "ctrl != cam.controller.get()";
203.         assert mice == ctrl.mouse.get() : "mice != ctrl.mouse.get()";
204.  
205.         cam.controller.set(null);
206.         assert null == ctrl.camera.get() : "null != ctrl.camera.get()";
207.  
208.     }
209. }
210.  
211. ////////////////////////////////////////////////////////////////////////////////
212.