Added in API level 1
Deprecated in API level 33

Summary: Ctors | Methods | Protected Methods | Inherited Methods

Observable

public class Observable
extends Object

java.lang.Object
↳	java.util.Observable

Known direct subclasses

ContentQueryMap

ContentQueryMap Caches the contents of a cursor into a Map of String->ContentValues and optionally keeps the cache fresh by registering for updates on the content backing the cursor.

This class was deprecated in API level 33.
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.

See also:

Summary

Public constructors
`Observable()` Construct an Observable with zero Observers.

Public methods
`void`	`addObserver(Observer o)` 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.
`int`	`countObservers()` Returns the number of observers of this `Observable` object.
`void`	`deleteObserver(Observer o)` Deletes an observer from the set of observers of this object.
`void`	`deleteObservers()` Clears the observer list so that this object no longer has any observers.
`boolean`	`hasChanged()` Tests if this object has changed.
`void`	`notifyObservers(Object arg)` 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()` 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 methods
`void`	`clearChanged()` 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`.
`void`	`setChanged()` Marks this `Observable` object as having been changed; the `hasChanged` method will now return `true`.

Inherited methods

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Public constructors

Observable

Added in API level 1

public Observable ()

Construct an Observable with zero Observers.

Public methods

addObserver

Added in API level 1

public void addObserver (Observer o)

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`	`Observer`: an observer to be added.

Throws
`NullPointerException`	if the parameter o is null.

countObservers

Added in API level 1

public int countObservers ()

Returns the number of observers of this Observable object.

Returns
`int`	the number of observers of this object.

deleteObserver

Added in API level 1

public void deleteObserver (Observer o)

Deletes an observer from the set of observers of this object. Passing null to this method will have no effect.

Parameters
`o`	`Observer`: the observer to be deleted.

deleteObservers

Added in API level 1

public void deleteObservers ()

Clears the observer list so that this object no longer has any observers.

hasChanged

Added in API level 1

public boolean hasChanged ()

Tests if this object has changed.

Returns
`boolean`	`true` if and only if the `setChanged` method has been called more recently than the `clearChanged` method on this object; `false` otherwise.

See also:

clearChanged()
setChanged()

notifyObservers

Added in API level 1

public void notifyObservers (Object arg)

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`	`Object`: any object.

See also:

notifyObservers

Added in API level 1

public void notifyObservers ()

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:

Protected methods

clearChanged

Added in API level 1

protected void clearChanged ()

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:

setChanged

Added in API level 1

protected void setChanged ()

Marks this Observable object as having been changed; the hasChanged method will now return true.