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isa(integer,thing). isa(person,thing). isa(man nodes. ▫ isa/2 captures the subclass relation hasa(person,sex,type,oneof(male,female)). hasa(person,sex . In an object-oriented design, there are two basic relationships between various objects: the "IsA" and "HasA" relationships. In this example, a. Hi all I am bit confusing with is-a, has-a and uses-a relationship of class, I know it's a basic concepts of OOPS and Inheritance. Is there any.
Since Engine is-part-of Car, the relationship between them is Composition. Here is how they are implemented between Java classes. Similar way is used to show aggregation and composition between two classes.
Composition VS Inheritance
Here are UML notations for different kind of dependency between two classes. As I said all three denotes relationship between object and only differ in their strength, you can also view them as below, where composition represents strongest form of relationship and association being the most general form.
Association vs Composition vs Aggregation Here is the list of differences between Composition and Aggregation in point format, for quick review.
An example is Car and Engine. While if A and B are associated with each other, such that B can exist without being associated with A, then this association in known as Aggregation. Organization uses People as an employee.
Since in Composition, Owner object expects a part object to be available and functions, by making it final, your provide guarantee that, when Owner will be created, this part object will exist. This is actually a Java idiom to represent a strong form of association i. If one object is-part-of another object e. Engine is part of Car, then association or relationship between them is Composition.
Types Of Relationships In Object Oriented Programming (OOPS)
On the other hand, if one object just has another object e. Car has the driver then it's Aggregation. We still can't do that dynamically. Enter the Decorator Pattern The problem we're discussing lends itself well to a Decorator-based solution. Beverages will be Components and we're going to add one CondimentDecorator for each condiment type. These Decorators will be composable, allowing for the dynamic creation of any coffee-condiment combination we need.
First, we need to extract an abstract Coffee type to hold the common functionality that all drinks need to provide - the GetDescription and GetCost methods. We'll use an interface for that and call it ICoffee: Then we can finally write our abstract decorator, which we'll call CondimentDecorator: The calls to GetDescription get intercepted and the description of the wrapped object is appended to the description of the condiment.Has-a and Is-a Relationships
Similarly, the cost of the wrapped object is added to the cost of the condiment in GetCost. The following diagram illustrates the call sequence that takes place when a GetCost call is being made on a top-level decorator. Cons All the advantages listed above were gained at the price of adding a couple of classes to our design.
This extra complexity is, however, minimal and completely worth our time.
The only thing that doesn't look so nice about the resulting code is the constructor chain: Conclusion We saw a brief formal introduction of the Decorator Pattern and then we had a look at a concrete problem that this construct is a natural fit for. Another example could have been a Pizza shop or a Car or Bike configurator. Anything that deals with objects whose behaviors should be extendable dynamically would do.