Callbacks
methods are the way of managing life cycle of an instance. Callback
methods are generally used by containers. The methods are called at
specific time during the lifetime of an instance. For example in
servlet destroy() method is called by the servlet container that
indicates that the servlet is being taken out of service. This type
of methods are generally called by the container, the developer does
not need to call these methods explicitly. Most of the languages
specifies the callback method by passing the address of the
subroutine to the system to the request is calling back from, But
java performs the same thing by using interfaces. Java does not allow
passing the address of subroutine but allows passing an instance of a
class that implements the standard interface. For this purpose
anonymous classes are mainly used as they support a better compact
definition of the class that is required as a new class.
One
more example of callback methods is ejbCreate method that is used by
an ejb container to create a ejb bean - the developer does not call
it explicitly in code- the container calls it- although the developer
can override it- or put stuff in it...
Callback
methods have totally different meaning regarding the context of
security. In order to login securely call the server which then calls
us back. This makes it harder for you to spoof being someone else.
This may be done over phone lines or over the Internet. It is the
same scheme a jealous husband might use to ensure his wife is really
home as she claims.
Callback can be used when you want to invoke some methods on the basis of some property changes. Suppose you want to call a piece of code of another class automatically when there is a change in property. Or you have a single property that is used by more than one classes to do some work. So when the value of this property is changed you want to notify those classes so that they can do their work with this updated value.
Callback can be used when you want to invoke some methods on the basis of some property changes. Suppose you want to call a piece of code of another class automatically when there is a change in property. Or you have a single property that is used by more than one classes to do some work. So when the value of this property is changed you want to notify those classes so that they can do their work with this updated value.
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