Module java.base
Package java.util

# Interface Observer

@Deprecated(since="9") public interface Observer
Deprecated.
This interface has been deprecated. See the `Observable` class for further information.
A class can implement the `Observer` interface when it wants to be informed of changes in observable objects.

Since:
  1.0
See Also:
  - `Observable`

## Method Summary

Modifier and Type
Method
Description
`void`
`update(Observable o, Object arg)`
Deprecated.
This method is called whenever the observed object is changed.

## Method Details

### update

void update(Observable o, Object arg)
Deprecated.
This method is called whenever the observed object is changed. An application calls an `Observable` object's `notifyObservers` method to have all the object's observers notified of the change.

Parameters:
  `o` - the observable object.
  `arg` - an argument passed to the `notifyObservers` method.