In this post, we will quickly review the design patterns:
First is the singleton pattern. Some of the core system functions are commonly accessed via a singleton pattern. Remember to use static, remember to hide the constructor, remember to count instances and remember to make it thread safe.
Builder is another pattern. The builder creates an object on your behalf in a step wise manner without knowing how it is created. This is very common to see in object relational mapping where we use a construct like
new Table().AddColumn().AddColumn().AddColumn(). .. etc
instead of Table(col1, col2, col3);
Another advantage is that it can create a hierarchy of builders.
Factory method pattern applies a concept of a factory method which is one that creates and returns an object.
An Abstract factory is one which creates other objects. This helps use many factories to create objects usually when they are of the same kind. There is a separation between the concrete classes and the callers of the factory.
An Observer pattern is one that is also called a Publish-Subscribe pattern or pub-sub pattern for short. Observers register themselves with the subject using an interface for update notifications. The model view controller is an example of this pattern because changes to the model automatically update the views.
One caveat in the observer pattern is that when there are frequent updates, the object may have to spend a lot of time notifying its observers. This is particularly true when there are multiple properties getting updated. It would then be better to consolidate the updates. Also the subject could pass the information on what has changed.
Decorator patterns are often applied in wrappers. The behavior of the underlying object is changed by the decorator.
A decorator is very different from an interface. While provide methods for certain behavior from the underlying objects. In one the object is wrapped and presented as another object while in the latter the object itself provides the desired behavior. Typically a decorator is used when the behavior has to be radically changed.
Using the decorator also helps avoid class explosion when there are many different behaviors added to an object.
First is the singleton pattern. Some of the core system functions are commonly accessed via a singleton pattern. Remember to use static, remember to hide the constructor, remember to count instances and remember to make it thread safe.
Builder is another pattern. The builder creates an object on your behalf in a step wise manner without knowing how it is created. This is very common to see in object relational mapping where we use a construct like
new Table().AddColumn().AddColumn().AddColumn(). .. etc
instead of Table(col1, col2, col3);
Another advantage is that it can create a hierarchy of builders.
Factory method pattern applies a concept of a factory method which is one that creates and returns an object.
An Abstract factory is one which creates other objects. This helps use many factories to create objects usually when they are of the same kind. There is a separation between the concrete classes and the callers of the factory.
An Observer pattern is one that is also called a Publish-Subscribe pattern or pub-sub pattern for short. Observers register themselves with the subject using an interface for update notifications. The model view controller is an example of this pattern because changes to the model automatically update the views.
One caveat in the observer pattern is that when there are frequent updates, the object may have to spend a lot of time notifying its observers. This is particularly true when there are multiple properties getting updated. It would then be better to consolidate the updates. Also the subject could pass the information on what has changed.
Decorator patterns are often applied in wrappers. The behavior of the underlying object is changed by the decorator.
A decorator is very different from an interface. While provide methods for certain behavior from the underlying objects. In one the object is wrapped and presented as another object while in the latter the object itself provides the desired behavior. Typically a decorator is used when the behavior has to be radically changed.
Using the decorator also helps avoid class explosion when there are many different behaviors added to an object.
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