Editing Adapter pattern (section)

==Structure==
=== UML class diagram ===
[[File:w3sDesign Adapter Design Pattern UML.jpg|frame|none|A sample UML class diagram for the adapter design pattern.<ref name="Structure"/>]]

In the above [[Unified Modeling Language|UML]] [[class diagram]], the <code>client</code> class that requires a <code>target</code> interface cannot reuse the <code>adaptee</code> class directly because its interface doesn't conform to the <code>target</code> interface.
Instead, the <code>client</code> works through an <code>adapter</code> class that implements the <code>target</code> interface in terms of <code>adaptee</code>:

* The <code>object adapter</code> way implements the <code>target</code> interface by delegating to an <code>adaptee</code> object at run-time (<code>adaptee.specificOperation()</code>). 
* The <code>class adapter</code> way implements the <code>target</code> interface by inheriting from an <code>adaptee</code> class at compile-time (<code>specificOperation()</code>).

===Object adapter pattern===
In this adapter pattern, the adapter contains an instance of the class it wraps. In this situation, the adapter makes calls to the instance of the wrapped [[object (computing)|object]].

[[File:ObjectAdapter.png|thumb|300px|center|The object adapter pattern expressed in [[Unified Modeling Language|UML]]]]
[[File:Adapter(Object) pattern in LePUS3.png|thumb|500px|center|The object adapter pattern expressed in [[Lepus3|LePUS3]]]]

===Class adapter pattern===
This adapter pattern uses multiple [[Subtyping|polymorphic interfaces]] implementing or inheriting both the interface that is expected and the interface that is pre-existing. It is typical for the expected interface to be created as a pure [[Interface (Java)|interface]] class, especially in [[programming language|languages]] such as [[Java (programming language)|Java]] (before JDK 1.8) that do not support [[multiple inheritance]] of classes.<ref name="HeadFirst"/>

[[File:ClassAdapter.png|thumb|300px|center|The class adapter pattern expressed in [[Unified Modeling Language|UML]].]]
[[File:Adapter(Class) pattern in LePUS3.png|thumb|500px|center|The class adapter pattern expressed in [[Lepus3|LePUS3]]]]

===A further form of runtime adapter pattern===
====Motivation from compile time solution====
It is desired for {{Java|classA}} to supply {{Java|classB}} with some data, let us suppose some {{Java|String}} data. A compile time solution is:

<syntaxhighlight lang=Java>
classB.setStringData(classA.getStringData());
</syntaxhighlight>

However, suppose that the format of the string data must be varied. A compile time solution is to use inheritance:

<syntaxhighlight lang=Java>
public class Format1ClassA extends ClassA {
    @Override
    public String getStringData() {
        return format(toString());
    }
}
</syntaxhighlight>

and perhaps create the correctly "formatting" object at runtime by means of the [[factory pattern]].

====Run-time adapter solution====
A solution using "adapters" proceeds as follows:
{{ordered list|list-style-type=lower-roman
|Define an intermediary "provider" interface, and write an implementation of that provider interface that wraps the source of the data, {{Java|ClassA}} in this example, and outputs the data formatted as appropriate:

<syntaxhighlight lang=Java>
public interface StringProvider {
    public String getStringData();
}

public class ClassAFormat1 implements StringProvider {
    private ClassA classA = null;

    public ClassAFormat1(final ClassA a) {
        classA = a;
    }

    public String getStringData() {
        return format(classA.getStringData());
    }

    private String format(final String sourceValue) {
        // Manipulate the source string into a format required 
        // by the object needing the source object's data
        return sourceValue.trim();
    }
}
</syntaxhighlight>

|Write an adapter class that returns the specific implementation of the provider:

<syntaxhighlight lang=Java>
public class ClassAFormat1Adapter extends Adapter {
    public Object adapt(final Object anObject) {
        return new ClassAFormat1((ClassA) anObject);
    }
}
</syntaxhighlight>

|Register the {{Java|adapter}} with a global registry, so that the {{Java|adapter}} can be looked up at runtime:

<syntaxhighlight lang=Java>
AdapterFactory.getInstance().registerAdapter(ClassA.class, ClassAFormat1Adapter.class, "format1");
</syntaxhighlight>

|In code, when wishing to transfer data from {{Java|ClassA}} to {{Java|ClassB}}, write:

<syntaxhighlight lang=Java>
Adapter adapter =
    AdapterFactory.getInstance()
        .getAdapterFromTo(ClassA.class, StringProvider.class, "format1");
StringProvider provider = (StringProvider) adapter.adapt(classA);
String string = provider.getStringData();
classB.setStringData(string);
</syntaxhighlight>

or more concisely:

<syntaxhighlight lang=Java>
classB.setStringData(
    ((StringProvider)
            AdapterFactory.getInstance()
                .getAdapterFromTo(ClassA.class, StringProvider.class, "format1")
                .adapt(classA))
        .getStringData());
</syntaxhighlight>

|The advantage can be seen in that, if it is desired to transfer the data in a second format, then look up the different adapter/provider:

<syntaxhighlight lang=Java>
Adapter adapter =
    AdapterFactory.getInstance()
        .getAdapterFromTo(ClassA.class, StringProvider.class, "format2");
</syntaxhighlight>

|And if it is desired to output the data from {{Java|ClassA}} as, say, image data in {{Java|Class C}}:
<syntaxhighlight lang=Java>
Adapter adapter =
    AdapterFactory.getInstance()
        .getAdapterFromTo(ClassA.class, ImageProvider.class, "format2");
ImageProvider provider = (ImageProvider) adapter.adapt(classA);
classC.setImage(provider.getImage());
</syntaxhighlight>

|In this way, the use of adapters and providers allows multiple "views" by {{Java|ClassB}} and {{Java|ClassC}} into {{Java|ClassA}} without having to alter the class hierarchy. In general, it permits a mechanism for arbitrary data flows between objects that can be retrofitted to an existing object hierarchy.
}}
<!-- Wikipedia is not a list of examples. Do not add examples from your favorite programming language here; this page exists to explain the design pattern, not to show how it interacts with subtleties of every language under the sun. Feel free to add examples here: http://en.wikibooks.org/wiki/Computer_Science/Design_Patterns/Adapter -->

===Implementation of the adapter pattern===
When implementing the adapter pattern, for clarity, one can apply the class name {{Java|[ClassName]To[Interface]Adapter}} to the provider implementation; for example, {{Java|DAOToProviderAdapter}}. It should have a constructor method with an adaptee class variable as a parameter. This parameter will be passed to an instance member of {{Java|[ClassName]To[Interface]Adapter}}. When the clientMethod is called, it will have access to the adaptee instance that allows for accessing the required data of the adaptee and performing operations on that data that generates the desired output.

====Java====
<syntaxhighlight lang=Java>
interface ILightningPhone {
    void recharge();
    void useLightning();
}

interface IMicroUsbPhone {
    void recharge();
    void useMicroUsb();
}

class Iphone implements ILightningPhone {
    private boolean connector;

    @Override
    public void useLightning() {
        connector = true;
        System.out.println("Lightning connected");
    }

    @Override
    public void recharge() {
        if (connector) {
            System.out.println("Recharge started");
            System.out.println("Recharge finished");
        } else {
            System.out.println("Connect Lightning first");
        }
    }
}

class Android implements IMicroUsbPhone {
    private boolean connector;

    @Override
    public void useMicroUsb() {
        connector = true;
        System.out.println("MicroUsb connected");
    }

    @Override
    public void recharge() {
        if (connector) {
            System.out.println("Recharge started");
            System.out.println("Recharge finished");
        } else {
            System.out.println("Connect MicroUsb first");
        }
    }
}
/* exposing the target interface while wrapping source object */
class LightningToMicroUsbAdapter implements IMicroUsbPhone {
    private final ILightningPhone lightningPhone;

    public LightningToMicroUsbAdapter(ILightningPhone lightningPhone) {
        this.lightningPhone = lightningPhone;
    }

    @Override
    public void useMicroUsb() {
        System.out.println("MicroUsb connected");
        lightningPhone.useLightning();
    }

    @Override
    public void recharge() {
        lightningPhone.recharge();
    }
}

public class AdapterDemo {
    static void rechargeMicroUsbPhone(IMicroUsbPhone phone) {
        phone.useMicroUsb();
        phone.recharge();
    }

    static void rechargeLightningPhone(ILightningPhone phone) {
        phone.useLightning();
        phone.recharge();
    }

    public static void main(String[] args) {
        Android android = new Android();
        Iphone iPhone = new Iphone();

        System.out.println("Recharging android with MicroUsb");
        rechargeMicroUsbPhone(android);

        System.out.println("Recharging iPhone with Lightning");
        rechargeLightningPhone(iPhone);

        System.out.println("Recharging iPhone with MicroUsb");
        rechargeMicroUsbPhone(new LightningToMicroUsbAdapter (iPhone));
    }
}
</syntaxhighlight>

Output
<pre>
Recharging android with MicroUsb
MicroUsb connected
Recharge started
Recharge finished
Recharging iPhone with Lightning
Lightning connected
Recharge started
Recharge finished
Recharging iPhone with MicroUsb
MicroUsb connected
Lightning connected
Recharge started
Recharge finished
</pre>

====Python====
<syntaxhighlight lang="python">
"""
Adapter pattern example.
"""
from abc import ABCMeta, abstractmethod

NOT_IMPLEMENTED = "You should implement this."

RECHARGE = ["Recharge started.", "Recharge finished."]

POWER_ADAPTERS = {"Android": "MicroUSB", "iPhone": "Lightning"}

CONNECTED = "{} connected."
CONNECT_FIRST = "Connect {} first."

class RechargeTemplate(metaclass=ABCMeta):

    @abstractmethod
    def recharge(self):
        raise NotImplementedError(NOT_IMPLEMENTED)

class FormatIPhone(RechargeTemplate):
    @abstractmethod
    def use_lightning(self):
        raise NotImplementedError(NOT_IMPLEMENTED)

class FormatAndroid(RechargeTemplate):
    @abstractmethod
    def use_micro_usb(self):
        raise NotImplementedError(NOT_IMPLEMENTED)

class IPhone(FormatIPhone):
    __name__ = "iPhone"

    def __init__(self):
        self.connector = False

    def use_lightning(self):
        self.connector = True
        print(CONNECTED.format(POWER_ADAPTERS[self.__name__]))

    def recharge(self):
        if self.connector:
            for state in RECHARGE:
                print(state)
        else:
            print(CONNECT_FIRST.format(POWER_ADAPTERS[self.__name__]))

class Android(FormatAndroid):
    __name__ = "Android"

    def __init__(self):
        self.connector = False

    def use_micro_usb(self):
        self.connector = True
        print(CONNECTED.format(POWER_ADAPTERS[self.__name__]))

    def recharge(self):
        if self.connector:
            for state in RECHARGE:
                print(state)
        else:
            print(CONNECT_FIRST.format(POWER_ADAPTERS[self.__name__]))

class IPhoneAdapter(FormatAndroid):
    def __init__(self, mobile):
        self.mobile = mobile

    def recharge(self):
        self.mobile.recharge()

    def use_micro_usb(self):
        print(CONNECTED.format(POWER_ADAPTERS["Android"]))
        self.mobile.use_lightning()

class AndroidRecharger:
    def __init__(self):
        self.phone = Android()
        self.phone.use_micro_usb()
        self.phone.recharge()

class IPhoneMicroUSBRecharger:
    def __init__(self):
        self.phone = IPhone()
        self.phone_adapter = IPhoneAdapter(self.phone)
        self.phone_adapter.use_micro_usb()
        self.phone_adapter.recharge()

class IPhoneRecharger:
    def __init__(self):
        self.phone = IPhone()
        self.phone.use_lightning()
        self.phone.recharge()

print("Recharging Android with MicroUSB recharger.")
AndroidRecharger()
print()

print("Recharging iPhone with MicroUSB using adapter pattern.")
IPhoneMicroUSBRecharger()
print()

print("Recharging iPhone with iPhone recharger.")
IPhoneRecharger()
</syntaxhighlight>

==== C# ====
<syntaxhighlight lang="c#">
public interface ILightningPhone
{
	void ConnectLightning();
	void Recharge();
}

public interface IUsbPhone
{
	void ConnectUsb();
	void Recharge();
}

public sealed class AndroidPhone : IUsbPhone
{
	private bool isConnected;

	public void ConnectUsb()
	{
		this.isConnected = true;
		Console.WriteLine("Android phone connected.");
	}

	public void Recharge()
	{
		if (this.isConnected)
		{
			Console.WriteLine("Android phone recharging.");
		}
		else
		{
			Console.WriteLine("Connect the USB cable first.");
		}
	}
}

public sealed class ApplePhone : ILightningPhone
{
	private bool isConnected;

	public void ConnectLightning()
	{
		this.isConnected = true;
		Console.WriteLine("Apple phone connected.");
	}

	public void Recharge()
	{
		if (this.isConnected)
		{
			Console.WriteLine("Apple phone recharging.");
		}
		else
		{
			Console.WriteLine("Connect the Lightning cable first.");
		}
	}
}

public sealed class LightningToUsbAdapter : IUsbPhone
{
	private readonly ILightningPhone lightningPhone;

	private bool isConnected;

	public LightningToUsbAdapter(ILightningPhone lightningPhone)
	{
		this.lightningPhone = lightningPhone;
	}

	public void ConnectUsb()
	{
		this.lightningPhone.ConnectLightning();
	}

	public void Recharge()
	{
		this.lightningPhone.Recharge();
	}
}

public void Main()
{
	ILightningPhone applePhone = new ApplePhone();
	IUsbPhone adapterCable = new LightningToUsbAdapter(applePhone);
	adapterCable.ConnectUsb();
	adapterCable.Recharge();
}
</syntaxhighlight>Output:<syntaxhighlight lang="output">
Apple phone connected.
Apple phone recharging.
</syntaxhighlight>