Real life example:
A very simple example is using phone charger. Suppose your mobile phone needs 9 Volts of supply to get charged but main supply is 220 V which is not what you require but it can be a source and you can have something that can get 9 V out of this 220 V and supply to your phone for charging.
Now phone charger is acting as an adapter for you. So Basically it is making a relationship between two unrelated interfaces. This is how Adpater pattern works.
Intent:
Also known as:
Wrapper
UML diagram of generic adapter design pattern:
Elements:
- Target
- defines domains-specific interface client uses.
- Client
- collaborates with objects conforming to target interface.
- Adaptee
- defines existing interface that needs adapting
- Adapter
- adapts the interface of adaptee to target interface.
WorkFlow:
Clients call operations on the adapter instance.In turn adapter calls adaptee operations that carry out the request.
When to use it:
- You want to use existing class and its interface does not match the one you need.
- You want to create a resuable class that cooperates with unrelated or unforeseen classes that is, class that don’t necessarily have compatible interfaces.
Example:
Comparing to above generic description of adapter pattern.
- PrintableList(Target)
- PrintString(Adaptee)
- PrintableListAdapter(Adapter)
Java code for all above classes:
Consider that we have a third party library that provides print string functionality through PrintString class.
This is our Adaptee. I know this is silly assumpsion but lets go with it for now.
PrintString.java(Adaptee) :
package org.arpit.javapostsforlearning.designpatterns;
public class PrintString {
public void print(String s)
{
System.out.println(s);
}
}
Client deals with ArrayList but not with string.We have provided a PrintableList interface that expects the client input.This is our target.
PrintableList.java(Target):
package org.arpit.javapostsforlearning.designpatterns;
import java.util.ArrayList;
public interface PrintableList {
void printList(ArrayList list);
}
Lets assume we can not change it now.
Finally we have PrintableListAdapter class which will implement PrintableList interface and will deal with our adaptee class.
PrintableListAdapter.java(Adapter):
package org.arpit.javapostsforlearning.designpatterns;
import java.util.ArrayList;
public class PrintableListAdapter implements PrintableList{
public void printList(ArrayList list) {
//Converting ArrayList to String so that we can pass String to
// adaptee class
String listString = "";
for (String s : list)
{
listString += s + "t";
}
// instantiating adaptee class
PrintString printString=new PrintString();
ps.print(listString);
}
}
AdapterDesignPatternMain.java:
package org.arpit.javapostsforlearning.designpatterns;
import java.util.ArrayList;
public class AdapterDesignPatternMain {
public static void main(String[] args)
{
ArrayList list=new ArrayList();
list.add("one");
list.add("two");
list.add("three");
PrintableList pl=new PrintableListAdapter();
pl.printList(list);
}
}
Output:
one two three
