Observer (Java SE 11 & JDK 11 )
Keywords: java.util.Observer interface

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

    All Methods Instance Methods Abstract Methods Deprecated Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `void` | `update​(Observable o, Object arg)` | Deprecated. This method is called whenever the observed object is changed.

- - ### Method Detail

    - #### 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.