Patterns – Day 4 Interfaces and Adapter Reminders: Faculty candidate talks Monday and Thursday. No...
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Transcript of Patterns – Day 4 Interfaces and Adapter Reminders: Faculty candidate talks Monday and Thursday. No...
Patterns – Day 4
Interfaces and Adapter
Reminders: Faculty candidate talks Monday and Thursday.No class on Monday.
Quotes from James Cooper
The [patterns] field has developed its own jargon.
Some writing on this subject has been a bit obscure.
Learning about Design Patterns entitles you to join an elite fraternity with its own language.
GoF Design Pattern Organization (slide by James Cooper)
Creational Structural BehavioralAbstract Factory Adapter Chain of
ResponsibilityBuilder Bridge CommandFactory Composite InterpreterPrototype Decorator IteratorSingleton Facade Mediator
Flyweight MementoProxy Observer
StateStrategyTemplateVisitor
Metsker Design Pattern Organization
Interface Responsibility Construction
Abstract Factory
Adapter
Chain of Responsibility
Builder
Bridge Command
FactoryComposite
InterpreterPrototype
DecoratorIterator
SingletonFacade
Mediator
Flyweight MementoProxy
Observer StateStrategy
Template
Visitor
Operation Extension
Interfaces
Why do you think Metsker included this chapter that’s basically just about Java interfaces?
Adapter Pattern
GoF Definition:
• Intent: Convert the interface of a class into another interface that clients expect.
• Adapter lets classes work together that otherwise couldn’t because of incompatible interfacer.
• Also known as Wrapper.
Let’s consider the Java awt.List and JList
• The awt.List is easier to use– But not very good looking– Hardly light weight
public List(int rows) ;
public void add(String item) ;
public void clear() ;
public void remove(int position) ;
public String[] getSelectedItems() ;
JList is an improvement
• Better looking
• More flexible
• But much harder to usepublic JList(ListModel dataModel) ;
• Everything else takes place in the data model.
Define a JawtList class
• Uses JList
• But has awt.List methods
public interface awtList { public void add(String s); public void remove(String s); public String[] getSelectedItems(); public void clear();}
Here is most of such a class//this is a simple adapter class to//convert List awt methods to Swing methods
public class JawtList extends JScrollPane implements ListSelectionListener, awtList { private JList listWindow; private JListData listContents;
public JawtList(int rows) { listContents = new JListData(); listWindow = new JList(listContents); listWindow.setPrototypeCellValue("Abcdefg Hijkmnop"); getViewport().add(listWindow); }//----------------------------------------- public void add(String s) { listContents.addElement(s); }//----------------------------------------- public void remove(String s) { listContents.removeElement(s); }//----------------- public void clear() { listContents.clear();
}
This is an Adapter pattern
• An adapter class converts the interface of one class to another.
• There are two ways to do this– Derive a new class from old one and add new
methods (inheritance)– Create a class which contains old class and passes
method calls to it. (object containment)
• These are called– Class adapters, and– Object adapters
Here is how we used it
kidList = new JawtList(20);
//===
private void loadList(Vector v) {
kidList.clear();
Iterator iter = v.iterator();
while(iter.hasNext()){
Swimmer sw = (Swimmer) iter.next();
kidList.add(sw.getName());
}
}
GoF ExampleA Graphics toolkit may have a number of Shape objects that can be manipulated in a certain way (BoundingBox, CreateManipulator).
There is no TextShape class, but there is TextView, which provides the needed functionality, but not the expected interface.
GoF general situation
In Java, Target would probably be an interface.
Target (Shape) defines the interface that client uses.
Client (DrawingEditor) collaborates with objects conforming to the Target interface.
Adaptee (TextView) defines an existing interface that needs to be adapted
Adapter (TextShape) adapts the interface of Adaptee to the Target interface.