Observer (Java SE 15 & JDK 15)
Description: declaration: module: java.base, package: java.util, interface: Observer
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

  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.