Module java.base
Package java.util

Class Observable

java.lang.Object
java.util.Observable
@Deprecated(since="9") public class Observable extends Object
Deprecated.
This class and the Observer interface have been deprecated. The event model supported by Observer and Observable is quite limited, the order of notifications delivered by Observable is unspecified, and state changes are not in one-for-one correspondence with notifications. For a richer event model, consider using the java.beans package. For reliable and ordered messaging among threads, consider using one of the concurrent data structures in the java.util.concurrent package. For reactive streams style programming, see the Flow API.
This class represents an observable object, or "data" in the model-view paradigm. It can be subclassed to represent an object that the application wants to have observed.

An observable object can have one or more observers. An observer may be any object that implements interface Observer. After an observable instance changes, an application calling the Observable's notifyObservers method causes all of its observers to be notified of the change by a call to their update method.

The order in which notifications will be delivered is unspecified. The default implementation provided in the Observable class will notify Observers in the order in which they registered interest, but subclasses may change this order, use no guaranteed order, deliver notifications on separate threads, or may guarantee that their subclass follows this order, as they choose.

Note that this notification mechanism has nothing to do with threads and is completely separate from the wait and notify mechanism of class Object.

When an observable object is newly created, its set of observers is empty. Two observers are considered the same if and only if the equals method returns true for them.

Since:
1.0
See Also:

  • Constructor Summary

    Constructors
    Constructor
    Description
    Observable()
    Deprecated.
    Construct an Observable with zero Observers.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    addObserver(Observer o)
    Deprecated.
    Adds an observer to the set of observers for this object, provided that it is not the same as some observer already in the set.
    protected void
    clearChanged()
    Deprecated.
    Indicates that this object has no longer changed, or that it has already notified all of its observers of its most recent change, so that the hasChanged method will now return false.
    int
    countObservers()
    Deprecated.
    Returns the number of observers of this Observable object.
    void
    deleteObserver(Observer o)
    Deprecated.
    Deletes an observer from the set of observers of this object.
    void
    deleteObservers()
    Deprecated.
    Clears the observer list so that this object no longer has any observers.
    boolean
    hasChanged()
    Deprecated.
    Tests if this object has changed.
    void
    notifyObservers()
    Deprecated.
    If this object has changed, as indicated by the hasChanged method, then notify all of its observers and then call the clearChanged method to indicate that this object has no longer changed.
    void
    notifyObservers(Object arg)
    Deprecated.
    If this object has changed, as indicated by the hasChanged method, then notify all of its observers and then call the clearChanged method to indicate that this object has no longer changed.
    protected void
    setChanged()
    Deprecated.
    Marks this Observable object as having been changed; the hasChanged method will now return true.

    Methods declared in class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • Observable

      public Observable()
      Deprecated.
      Construct an Observable with zero Observers.

  • Method Details

    • addObserver

      public void addObserver(Observer o)
      Deprecated.
      Adds an observer to the set of observers for this object, provided that it is not the same as some observer already in the set. The order in which notifications will be delivered to multiple observers is not specified. See the class comment.
      Parameters:
      o - an observer to be added.
      Throws:
      NullPointerException - if the parameter o is null.

    • deleteObserver

      public void deleteObserver(Observer o)
      Deprecated.
      Deletes an observer from the set of observers of this object. Passing null to this method will have no effect.
      Parameters:
      o - the observer to be deleted.

    • notifyObservers

      public void notifyObservers()
      Deprecated.
      If this object has changed, as indicated by the hasChanged method, then notify all of its observers and then call the clearChanged method to indicate that this object has no longer changed.

      Each observer has its update method called with two arguments: this observable object and null. In other words, this method is equivalent to:

      notifyObservers(null)
      See Also:

    • notifyObservers

      public void notifyObservers(Object arg)
      Deprecated.
      If this object has changed, as indicated by the hasChanged method, then notify all of its observers and then call the clearChanged method to indicate that this object has no longer changed.

      Each observer has its update method called with two arguments: this observable object and the arg argument.

      Parameters:
      arg - any object.
      See Also:

    • deleteObservers

      public void deleteObservers()
      Deprecated.
      Clears the observer list so that this object no longer has any observers.

    • setChanged

      protected void setChanged()
      Deprecated.
      Marks this Observable object as having been changed; the hasChanged method will now return true.

    • clearChanged

      protected void clearChanged()
      Deprecated.
      Indicates that this object has no longer changed, or that it has already notified all of its observers of its most recent change, so that the hasChanged method will now return false. This method is called automatically by the notifyObservers methods.
      See Also:

    • hasChanged

      public boolean hasChanged()
      Deprecated.
      Tests if this object has changed.
      Returns:
      true if and only if the setChanged method has been called more recently than the clearChanged method on this object; false otherwise.
      See Also:

    • countObservers

      public int countObservers()
      Deprecated.
      Returns the number of observers of this Observable object.
      Returns:
      the number of observers of this object.