ADAPTER

PATTERN

Adeel Riaz

Mirza Danish Baig

Malik Mohammad Sohaib

Farhan Ahmed

Advisor: Muhammad Qasim pasta

PAF KIET Fall 11

1

Real World Adapter

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Adapter in our Object Oriented

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Problem in Object Oriented??

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Problem in Object Oriented??

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I have already written class called xyzcircle that deals with circles already. But we can’t use directly because I want to preserve polymorphic behavior with Shape

PAF KIET Fall 11

Problem in Object Oriented??

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6

Intent

Convert the interface of a class into

another interface clients expect.

Adapter lets classes work together that

couldn't otherwise because of incompatible

interfaces.

Also Known As -> Wrapper

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Motivation

Sometimes a toolkit or class library can not

be used because its interface is incompatible

with the interface required by an application

We can not change the library interface,

since we may not have its source code

Even if we did have the source code, we

probably should not change the library for

each domain-specific application

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Motivation

Example:

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Applicability

Use the Adapter pattern when

You want to use an existing class, and

its interface does not match the one you

need

You want to create a reusable class

that cooperates with unrelated classes

with incompatible interfaces

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Structure An object adapter relies on object

composition:

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Participants

Target (Shape)• defines the domain-specific interface that Client uses.

Adapter (Line,TextShape)• adapts the interface Adaptee to the Target interface.

Adaptee (TextView)• defines an existing interface that needs adapting.

Client (DrawingEditor)• collaborates with objects conforming to the Target interface.

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Example

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Example

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Sequence Diagram

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Consequences

Class adapter

Concrete Adapter class

Unknown Adaptee subclasses might cause problem

Object adapter

Adapter can service many different Adaptees

May require the creation of Adaptee subclasses and

referencing those objects

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Implementation

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How much adapting should be done?

Simple interface conversion that just changes operation names and order of arguments

Totally different set of operations

Does the adapter provide two-way transparency?

A two-way adapter supports both the Target and the Adaptee interface. It allows an adapted object (Adapter) to appear as an Adaptee object or a Target object

PAF KIET Fall 11

Comparing the Facade Pattern with the

Adapter Pattern

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In both the Facade and Adapter pattern I have preexisting classes.

In the Facade, however, I do not have an interface I must design to, as I do in the Adapter

pattern.

I am not interested in polymorphic behavior in the Façade, while in the Adapter, I probably

am. (There are times when we just need to design to a particular API and therefore must use

an Adapter. In this case, polymorphism may not be an issue— that's why I say "probably").

In the case of the Facade pattern, the motivation is to simplify the interface. With the

Adapter, while simpler is better, I am trying to design to an existing interface and cannot

simplify things even if a simpler interface were otherwise possible.

PAF KIET Fall 11

Example 1

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Consider that we have a third party library that provides sorting functionality through it's NumberSorter class. This is our Adaptee

/*

* This is our adaptee, a third party implementation of a

* number sorter that deals with Lists, not arrays.

*/

public class NumberSorter

{

public List<Integer> sort(List<Integer> numbers)

{

//sort and return

return new ArrayList<Integer>();

}

}

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Example 1 (continued)

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Our Client deals with primitive arrays rather than Lists. For the sake of this example, lets say we can't change the client to use Lists.

We've provided a Sorter interface that expects the client input. This is our target.

//this is our Target interface

public interface Sorter

{

public int[] sort(int[] numbers);

}

PAF KIET Fall 11

Example 1 (continued)

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Finally, the SortListAdapter implements our target interface and deals with our adaptee, NumberSorter

public class SortListAdapter implements Sorter

{

@Override

public int[] sort(int[] numbers)

{

//convert the array to a List

List<Integer> numberList = new ArrayList<Integer>();

//call the adapter

NumberSorter sorter = new NumberSorter();

numberList = sorter.sort(numberList);

//convert the list back to an array and return

return sortedNumbers;

}

}

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Example 1 (Continued)

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int[] numbers = new int[]{34, 2, 4, 12, 1};

Sorter sorter = new SortListAdapter();

sorter.sort(numbers);

PAF KIET Fall 11

Questions?

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