java.util
public class
public class
java.util.Observable
| java.lang.Object | ||
| java.util.Observable | ||
Observable is used to notify a group of Observer objects when a change occurs.
Known Direct Subclasses
Summary
Public Constructors
| Observable() | |||||
| Constructs a new Observable object. | |||||
Public Methods
| synchronized | void | addObserver(Observer observer) | |||
| Adds the specified Observer to the list of observers. | |||||
| synchronized | int | countObservers() | |||
| Answers the number of Observers in the list of observers. | |||||
| synchronized | void | deleteObserver(Observer observer) | |||
| Removes the specified Observer from the list of observers. | |||||
| synchronized | void | deleteObservers() | |||
| Removes all Observers from the list of observers. | |||||
| synchronized | boolean | hasChanged() | |||
| Answers the changed flag for this Observable. | |||||
| void | notifyObservers() | ||||
If hasChanged() returns true, calls the update() method for
every Observer in the list of observers using null as the argument. |
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| void | notifyObservers(Object data) | ||||
If hasChanged() returns true, calls the update() method for
every Observer in the list of observers using the specified argument. |
|||||
Protected Methods
| synchronized | void | clearChanged() | |||
| Clears the changed flag for this Observable. | |||||
| synchronized | void | setChanged() | |||
| Sets the changed flag for this Observable. | |||||
Methods inherited
from class
java.lang.Object
Details
Public Constructors
public Observable()
Constructs a new Observable object.
Public Methods
public synchronized void addObserver(Observer observer)
Adds the specified Observer to the list of observers.
Parameters
| observer | the Observer to add |
|---|
public synchronized int countObservers()
Answers the number of Observers in the list of observers.
Returns
- the number of observers
public synchronized void deleteObserver(Observer observer)
Removes the specified Observer from the list of observers.
Parameters
| observer | the Observer to remove |
|---|
public synchronized void deleteObservers()
Removes all Observers from the list of observers.
public synchronized boolean hasChanged()
Answers the changed flag for this Observable.
Returns
- true when the changed flag for this Observable is set, false otherwise
public void notifyObservers()
If
hasChanged() returns true, calls the update() method for
every Observer in the list of observers using null as the argument.
Afterwards calls clearChanged().
Equivalent to calling notifyObservers(null)
public void notifyObservers(Object data)
If
hasChanged() returns true, calls the update() method for
every Observer in the list of observers using the specified argument.
Afterwards calls clearChanged().
Parameters
| data | the argument passed to update() |
|---|
Protected Methods
protected synchronized void clearChanged()
Clears the changed flag for this Observable. After calling
clearChanged(), hasChanged() will return false.
protected synchronized void setChanged()
Sets the changed flag for this Observable. After calling
setChanged(), hasChanged() will return true.