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## java.util
Interface Observer

public interface Observer

A class can implement the `Observer` interface when it wants to be informed of changes in observable objects.

Since:
  JDK1.0
See Also:
  `Observable`

Method Summary
`void` | `update(Observable o, Object arg)` This method is called whenever the observed object is changed.

Method Detail

### update

    public void update(Observable o,
                       Object arg)

  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.

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.