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docs: update observer

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Ilkka Seppälä
2024-05-26 21:32:06 +03:00
parent 5e133822ad
commit f655cee274
1 changed files with 48 additions and 17 deletions
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observer/README.md
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@@ -21,7 +21,7 @@ Define a one-to-many dependency between objects so that when one object changes
Real-world example
> In a land far away live the races of hobbits and orcs. Both of them are mostly outdoors so they closely follow the weather changes. One could say that they are constantly observing the weather.
> In a real-world example, consider a news agency system where the agency (subject) publishes news articles, and multiple news outlets (observers) subscribe to receive updates. Whenever the news agency publishes a new article, it automatically notifies all the subscribed news outlets. These outlets can then update their platforms (like websites, TV broadcasts, or newspapers) with the latest news. This ensures that all subscribers get the latest information without the news agency needing to know the specifics of each outlet's update process. This decouples the news agency from the subscribers, promoting flexibility and modularity in how updates are handled.
In plain words
@@ -33,6 +33,8 @@ Wikipedia says
**Programmatic Example**
In a land far away live the races of hobbits and orcs. Both of them are mostly outdoors, so they closely follow the weather changes. One could say that they are constantly observing the weather.
Let's first introduce the `WeatherObserver` interface and our races, `Orcs` and `Hobbits`.
```java
@@ -105,30 +107,58 @@ public class Weather {
Here's the full example in action.
```java
public static void main(String[] args) {
var weather = new Weather();
weather.addObserver(new Orcs());
weather.addObserver(new Hobbits());
weather.timePasses();
weather.timePasses();
weather.timePasses();
weather.timePasses();
// Generic observer inspired by Java Generics and Collections by Naftalin & Wadler
LOGGER.info("--Running generic version--");
var genericWeather = new GenWeather();
genericWeather.addObserver(new GenOrcs());
genericWeather.addObserver(new GenHobbits());
genericWeather.timePasses();
genericWeather.timePasses();
genericWeather.timePasses();
genericWeather.timePasses();
}
```
Program output:
```
The weather changed to rainy.
The orcs are facing rainy weather now
The hobbits are facing rainy weather now
The weather changed to windy.
The orcs are facing windy weather now
The hobbits are facing windy weather now
The weather changed to cold.
The orcs are facing cold weather now
The hobbits are facing cold weather now
The weather changed to sunny.
The orcs are facing sunny weather now
The hobbits are facing sunny weather now
21:28:08.310 [main] INFO com.iluwatar.observer.Weather -- The weather changed to rainy.
21:28:08.312 [main] INFO com.iluwatar.observer.Orcs -- The orcs are facing Rainy weather now
21:28:08.312 [main] INFO com.iluwatar.observer.Hobbits -- The hobbits are facing Rainy weather now
21:28:08.312 [main] INFO com.iluwatar.observer.Weather -- The weather changed to windy.
21:28:08.312 [main] INFO com.iluwatar.observer.Orcs -- The orcs are facing Windy weather now
21:28:08.312 [main] INFO com.iluwatar.observer.Hobbits -- The hobbits are facing Windy weather now
21:28:08.312 [main] INFO com.iluwatar.observer.Weather -- The weather changed to cold.
21:28:08.312 [main] INFO com.iluwatar.observer.Orcs -- The orcs are facing Cold weather now
21:28:08.312 [main] INFO com.iluwatar.observer.Hobbits -- The hobbits are facing Cold weather now
21:28:08.312 [main] INFO com.iluwatar.observer.Weather -- The weather changed to sunny.
21:28:08.312 [main] INFO com.iluwatar.observer.Orcs -- The orcs are facing Sunny weather now
21:28:08.312 [main] INFO com.iluwatar.observer.Hobbits -- The hobbits are facing Sunny weather now
21:28:08.312 [main] INFO com.iluwatar.observer.App -- --Running generic version--
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenWeather -- The weather changed to rainy.
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenOrcs -- The orcs are facing Rainy weather now
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenHobbits -- The hobbits are facing Rainy weather now
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenWeather -- The weather changed to windy.
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenOrcs -- The orcs are facing Windy weather now
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenHobbits -- The hobbits are facing Windy weather now
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenWeather -- The weather changed to cold.
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenOrcs -- The orcs are facing Cold weather now
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenHobbits -- The hobbits are facing Cold weather now
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenWeather -- The weather changed to sunny.
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenOrcs -- The orcs are facing Sunny weather now
21:28:08.313 [main] INFO com.iluwatar.observer.generic.GenHobbits -- The hobbits are facing Sunny weather now
```
## Class diagram
@@ -172,7 +202,8 @@ Trade-offs:
## Credits
* [Design Patterns: Elements of Reusable Object-Oriented Software](https://www.amazon.com/gp/product/0201633612/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0201633612&linkCode=as2&tag=javadesignpat-20&linkId=675d49790ce11db99d90bde47f1aeb59)
* [Java Generics and Collections](https://www.amazon.com/gp/product/0596527756/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596527756&linkCode=as2&tag=javadesignpat-20&linkId=246e5e2c26fe1c3ada6a70b15afcb195)
* [Head First Design Patterns: A Brain-Friendly Guide](https://www.amazon.com/gp/product/0596007124/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596007124&linkCode=as2&tag=javadesignpat-20&linkId=6b8b6eea86021af6c8e3cd3fc382cb5b)
* [Refactoring to Patterns](https://www.amazon.com/gp/product/0321213351/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0321213351&linkCode=as2&tag=javadesignpat-20&linkId=2a76fcb387234bc71b1c61150b3cc3a7)
* [Design Patterns: Elements of Reusable Object-Oriented Software](https://amzn.to/3w0pvKI)
* [Java Generics and Collections](https://amzn.to/3VhOBxp)
* [Head First Design Patterns: Building Extensible and Maintainable Object-Oriented Software](https://amzn.to/49NGldq)
* [Pattern-Oriented Software Architecture Volume 1: A System of Patterns](https://amzn.to/3xZ1ELU)
* [Refactoring to Patterns](https://amzn.to/3VOO4F5)