What is difference between Class Adapter and Object Adapter pattern?

[Avijeet Dash]

What is difference between Class Adapter and Object Adapter pattern?

[Laojar Chuger]

Pattern name is always a very confuse. Can you give a little bit more info on both patterns you mentioned.

[Thomas Paul]

I just had to do a presentation on this so it is funny you asked:
The difference is that an object adapter contains the adaptee while the class adapter inherits from the adaptee. Which to use is dependent on the specific requirements of your application. For example, if there are multiple adaptees, then you would use the object adapter.
Here is some sample code. In this case the old class is called OldReporter (and has been converted into an interface), the new class (the adaptee) is called NewReportWriter, and the adapter is named ReportGenerator.

// Object adapter version
public class ReportGenerator implements OldReporter {
    private NewReportWriter newReporter = new NewReportWriter();
    public void writeHeader(String headerData) {
        newReporter.generateHeaderLines(headerData);
    }
}
// Class adapter version
public class ReportGenerator extends NewReportWriter 
        implements OldReporter {
    public void writeHeader(String headerData) {
        generateHeaderLines(headerData);
    }
}

BTW, The GoF book does a nice job of explaining this pattern.
[This message has been edited by Thomas Paul (edited March 22, 2001).]

[Avijeet Dash]

makes sense.
Thanks.

[Thomas Paul]

As a college professor, "makes sense" are the words I always long to here! Thanks!
------------------
Moderator of the JDBC Forum

[Gurumurthy Ramamurthy]

Is this what the object adapter?
this.addWindowListener(
new WindowAdapter()
{
public void windowClosing(WindowEvent we)
{
System.exit(0);
}
});
regards,
Guru

[Ilja Preuss]

No, the AWT adapter classes do have nothing in common with the GOF Adapter patterns - they are simply empty stub implementations of interfaces. In fact I don't know why the Sun programmers decided to call them adapters - it's awkward, in my humble opinion...
Imagine you do have an Enumeration object and want to pass it to a method which expects an Iterator. You could do this by wrapping the Enumeration object into an implementation of the Iterator interface which just delegates calls to the appropriate methods of the Enumeration. That wrapper object would be an Object Adapter.
Did that help?

[RanjithSekar SekarRanjith]

public class AdapteePrintString {
public void printString(String printStr) {
System.out.println("inside AdapteePrintString>> " + printStr);
}
}

import java.util.List;
public interface TargetPrintList {
void printList(List<String> list);
}

Class Adapter:
import java.util.List;

public class AdapterPrintable extends AdapteePrintString implements TargetPrintList {
@Override
public void printList(List<String> list) {
String printString = "";
for (String str : list) {
printString = printString + " " + str;
}
printString(printString);
}
}


Object Adapter:
import java.util.List;
public class AdapterPrintable implements TargetPrintList {
@Override
public void printList(List<String> list) {
String printString = "";
for (String str : list) {
printString = printString + " " + str;
}
AdapteePrintString adapteePrintString = new AdapteePrintString();
adapteePrintString.printString(printString);
}
}

Testing the Adapters:
import java.util.ArrayList;
import java.util.List;
public class ClientTestAdapter {
public static void main(String[] args) {
TargetPrintList print = new AdapterPrintable();
List<String> myList = new ArrayList<String>();
myList.add("Ranjith");
myList.add("Sekar");
print.printList(myList);
}
}

Hope helps.......