Adapter Design Pattern
Adapter, a Structural Pattern and also referred to as a wrapper, is most commonly used when you want to reuse a class to work with a target class but are constrained by incompatible interfaces. The idea is to convert the interface of a reusable class into an interface that your classes expect.
A good analogy for the Adapter pattern would be the adapters that are commonly used to convert the voltage of Canadian/U.S made appliances to be used in different countries. In this case, the appliance (Target) is using the adapter (Adapter) to reuse the socket (Adaptee) already in place.
There are two specific types of adapter patterns - object adapter pattern and class adapter pattern. The latter uses multiple inheritance whereas the former uses an instance of the reuseable class it wants to adapt. Between the two, object adapter pattern is the favored one due to the fact that popular languages such as Java do not support multiple inheritance.
Object Adapter Pattern
This adapter pattern uses an instance of the class it wraps. By using an instance, methods belonging to the wrapped object can be invoked.
Class Adapter Pattern
This adapter pattern uses multiple inheritance as a means to wrap the reusable class and use its functionality.
Adapter UML Diagram
UML diagram example of the Adapter pattern. Specifically, the class adapter pattern
Image source: http://www.dofactory.com/Patterns/Diagrams/adapter.gif (Copyright 2001 - 2007 Data & Object Factory.)
Code Examples
Java
FreeMind - GNU General Public License. FreeMind's File Repository
In this example, an ArrowLinkAdapter is created to be used to adapt different arrow shaped links in FreeMind's MindMap area.
ArrowLinkAdapter.java
/*FreeMind - A Program for creating and viewing Mindmaps
*Copyright (C) 2000-2001 Joerg Mueller <joergmueller@bigfoot.com>
*See COPYING for Details
*
*This program is free software; you can redistribute it and/or
*modify it under the terms of the GNU General Public License
*as published by the Free Software Foundation; either version 2
*of the License, or (at your option) any later version.
*
*This program is distributed in the hope that it will be useful,
*but WITHOUT ANY WARRANTY; without even the implied warranty of
*MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
*GNU General Public License for more details.
*
*You should have received a copy of the GNU General Public License
*along with this program; if not, write to the Free Software
*Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
/*$Id: ArrowLinkAdapter.java,v 1.4 2003/12/07 21:00:19 christianfoltin Exp $*/
package freemind.modes;
import freemind.modes.LinkAdapter;
import freemind.main.FreeMindMain;
import java.awt.Point;
public abstract class ArrowLinkAdapter extends LinkAdapter implements MindMapArrowLink {
/** the zero is the start point of the line;*/
protected Point startInclination;
/** the zero is the start point of the line;*/
protected Point endInclination;
protected String startArrow;
protected String endArrow;
public ArrowLinkAdapter(MindMapNode source,MindMapNode target,FreeMindMain frame) {
super(source, target, frame, "standardlinkcolor", "standardlinkstyle");
startArrow = "None";
endArrow = "Default";
}
public Point getStartInclination() { return startInclination; }
public Point getEndInclination() { return endInclination; }
public String getStartArrow() { return startArrow; }
public String getEndArrow() { return endArrow; }
public void setStartInclination(Point startInclination) { this.startInclination=startInclination; }
public void setEndInclination(Point endInclination) { this.endInclination=endInclination; }
public void setStartArrow(String startArrow) {
if(startArrow == null || startArrow.toUpperCase().equals("NONE")) {
this.startArrow = "None";
return;
} else if(startArrow.toUpperCase().equals("DEFAULT")) {
this.startArrow = "Default";
return;
}
// dont change:
System.err.println("Cannot set the start arrow type to " + startArrow);
}
public void setEndArrow(String endArrow) {
if(endArrow == null || endArrow.toUpperCase().equals("NONE")) {
this.endArrow = "None";
return;
} else if(endArrow.toUpperCase().equals("DEFAULT")) {
this.endArrow = "Default";
return;
}
// dont change:
System.err.println("Cannot set the end arrow type to " + endArrow);
}
public Object clone() {
ArrowLinkAdapter arrowLink = (ArrowLinkAdapter) super.clone();
// now replace the points:
arrowLink.startInclination = (startInclination==null)?null:new Point(startInclination.x, startInclination.y);
arrowLink.endInclination = (endInclination==null)?null:new Point(endInclination.x, endInclination.y);
arrowLink.startArrow = (startArrow==null)?null:new String(startArrow);
arrowLink.endArrow = (endArrow==null)?null:new String(endArrow);
return arrowLink;
}
}
C++
KDEBluetooth - GNU General Public License
KDEBluetooth File Repository
adapter.h
//-*-c++-*-
/***************************************************************************
* Copyright (C) 2003 by Fred Schaettgen *
* kdebluetooth@0xF.de *
* *
* This program is free software; you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation; either version 2 of the License, or *
* (at your option) any later version. *
***************************************************************************/
#ifndef BTADAPTER_H
#define BTADAPTER_H
#include <vector>
#include <qstring.h>
#include <qvaluevector.h>
#include "deviceaddress.h"
namespace KBluetooth
{
/** Class representing a local bluetooth adapter.
* This class provides access to the properties of a local bluetooth
* adapter. This class has no public constructors. You can get the
* list of available adapters using KBluetooth::Adapters.
*/
class Adapter
{
friend class Adapters;
public:
enum ConnectionType { SCO = 0, ACL = 1 };
enum ConnectionState { NOT_CONNECTED, CONNECTED, CONNECTING, UNKNOWN_STATE };
struct ConnectionInfo {
DeviceAddress address;
int handle;
ConnectionType type;
ConnectionState state;
bool out;
uint link_mode;
};
typedef QValueVector<ConnectionInfo> ConnectionInfoVector;
/** Returns the device address of the given adapter.
@return The device address
*/
DeviceAddress getAddress() const;
/** Returns the name of the adapter.
@return The device name
*/
QString getName() const;
/** Returns the index of the device.
@return device index
*/
int getIndex() const;
/** Return a deviceaddress for each ACL-Connection */
ConnectionInfoVector getAclConnections() const;
ConnectionState getAclConnectionState(const DeviceAddress& addr) const;
protected:
/** Constructor used internally by KBluetooth::Adapters. */
Adapter(int index, const DeviceAddress& address, QString nameStr);
private:
int index;
QString nameStr;
DeviceAddress address;
};
/** Enumerates the locally attached bluetooth devices.
* The information in this class stays static until update()
* is called.
*/
class Adapters
{
public:
/** Default constructor.
Calls update().
*/
Adapters();
/** Gets the number of adapters.
@return number of adapters
*/
int count();
/** Returns a single adapter
@param n index of the adapter (0 <= n < count())
@return adapter info
*/
const Adapter& operator[](int n) const;
/** Refreshes the list of adapters. */
void update();
private:
std::vector<Adapter> adapters;
static int dev_info(int s, int dev_id, long arg);
void dev_info(int s, int dev_id);
};
}
#endif