Java 提供 Observable 不是一个好习惯

Question

public void update(Observable obs, Object arg) 
{
  if (obs instanceof WeatherData) {
  WeatherData weatherData = (WeatherData)obs;
  this.temperature = weatherData.getTemperature();
  this.humidity = weatherData.getHumidity();
  display();
  }
 }

The above piece of code is from Head First Design Patterns . An event is going to fire for every change that occurs, and this will be sent to all the observers whether the event is what they expect or not. The if block helps in letting the code decide which events to handle.

So create observable for every such scenario will be a good practice right?

Answer 1

So create observable for every such scenario will be a good practice right?

Yes! I have advocated this approach numerous times, for example here , here , and here . It perplexes me why people so often implement the Observer pattern with only one event class and then struggle to pass different types of events. By all means: create new event classes!