1
00:00:00,840 --> 00:00:07,350
The observer pattern is the one to many relationship between objects such that whenever an object changes

2
00:00:07,350 --> 00:00:11,590
its state, all of the connected objects will change their state as well.

3
00:00:12,060 --> 00:00:17,070
This pattern is characterised by two types of objects, observers and subjects.

4
00:00:18,080 --> 00:00:23,500
As you may have guessed, the observer will watch for any change in the subject's behavior.

5
00:00:24,460 --> 00:00:31,360
In the Java API, the Java Dots 820 Dunbarton is an example where the observer pattern has been used

6
00:00:31,630 --> 00:00:37,360
due to the fact that you can define a listener for a button and whenever the button is click, the listener

7
00:00:37,480 --> 00:00:39,610
is notified and some event is triggered.

8
00:00:41,200 --> 00:00:47,080
The UML diagram of this pattern looks like this, you have an observer interface and many observer objects

9
00:00:47,080 --> 00:00:47,860
that implemented.

10
00:00:48,750 --> 00:00:55,320
The observer listens for changes in the subjects object state, and whenever such change occurs and

11
00:00:55,320 --> 00:00:56,160
action is triggered.

12
00:00:57,900 --> 00:01:03,540
Some of the weaknesses of the spatter can be the fact that a large object would have a very big hit

13
00:01:03,540 --> 00:01:05,370
on the performance of the application.

14
00:01:06,300 --> 00:01:11,290
Think about working with very large files, and whenever there is an update, you need to choose something

15
00:01:11,320 --> 00:01:12,840
in a 500 megabytes file.

16
00:01:14,520 --> 00:01:19,860
Another weakness is that some updates can be a bit confusing, making debugging more difficult.

17
00:01:21,060 --> 00:01:22,980
Let's see how this pattern can be implemented.

18
00:01:23,070 --> 00:01:23,180
The.