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| Chapter 30 The java.util Package |

## 30.15 java.util.Observable (JDK 1.0)

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This class is the superclass of all "observable" objects to be used in an object-oriented model/view paradigm. The class methods allow you to add and delete `Observer` objects to and from an `Observable`'s list, and to notify all of the `Observer` objects on the list. `Observer` objects are "notified" by invoking their `update()` method. `Observable` also maintains an internal "changed" flag, which may be set and cleared by the `Observable`, and which may be queried with `hasChanged()` by any interested observer.

    public class Observable extends Object {
        // Public Constructor
            1.1public Observable();
        // Public Instance Methods
                public synchronized void addObserver(Observer o);
                public synchronized int countObservers();
                public synchronized void deleteObserver(Observer o);
                public synchronized void deleteObservers();
                public synchronized boolean hasChanged();
                public void notifyObservers();
                public void notifyObservers(Object arg);
        // Protected Instance Methods
                protected synchronized void clearChanged();
                protected synchronized void setChanged();
    }

### Passed To:

Observer.update()

java.util.NoSuchElementException (JDK 1.0) |  | java.util.Observer (JDK 1.0)