Java Patterns GDG

Charla para GDG

Transcript

1. Samstag, 24. November 12
2. What is a design pattern The solution of a coding problem Samstag, 24. November 12
3. What is a design pattern (extended) Language independent strategies OO Oriented Generally a reusable solution Not a final solution (template) Samstag, 24. November 12
4. More... At least 250 types1 Relationship between them -Exclusive 1The Design Patterns, Java Companion -- by James W. Cooper -Natural fitting -Leading Samstag, 24. November 12
5. Types Creational patterns 1The Design Patterns, Java Companion -- by James W. Cooper Creational patterns Behavioral patterns J2EE patterns Samstag, 24. November 12
6. Creational: Singleton One instance of a class or one value accessible globally in an application. -Ensure unique instance -Access instance controlled way -Define a value shared by all system Samstag, 24. November 12
7. Creational: Singleton final class RemoteConnection { private Connect con; private static RemoteConnection rc = new RemoteConnection(connection); private RemoteConnection(Connect c) { con = c; .... } public static RemoteConnection getRemoteConnection() { return rc; } public void setConnection(Connect c) { this(c); } } RemoteConnection rconn = RemoteConnection.getRemoteConnection; rconn.loadData(); Samstag, 24. November 12
8. Creational: Prototype Cloning an object by reducing the cost of creation. -Many subclasses, only differ object type -Add/remove objects and runtime -Configure an application dynamically Samstag, 24. November 12
9. Creational: Prototype interface Shape { public void draw(); } class Line implements Shape { public void draw() { System.out.println("line"); } } class Square implements Shape { public void draw() { System.out.println("square"); } } class Circle implements Shape { public void draw() { System.out.println("circle"); } } Samstag, 24. November 12
10. Creational: Prototype class Painting { public static void main(String[] args) { Shape s1 = new Line(); Shape s2 = new Square(); Shape s3 = new Circle(); paint(s1); paint(s2); paint(s3); } static void paint(Shape s) { s.draw(); } } Samstag, 24. November 12
11. Structural: Adapter Convert existing interfaces to a new interface to achieve compatibility and reusability. Also known as Wrapper pattern. Related: Proxy, Decorator or Bridge Samstag, 24. November 12
12. Structural: Adapter public interface Windowlistener { public void windowClosed(WindowEvent e); public void windowOpened(WindowEvent e); public void windowIconified(WindowEvent e); public void windowDeiconified(WindowEvent e); public void windowActivated(WindowEvent e); public void windowDeactivated(WindowEvent e); public void windowClosing(WindowEvent e); } public class WindowAdapter implements WindowListner{ public void windowClosed(WindowEvent e){} public void windowOpened(WindowEvent e){} public void windowIconified(WindowEvent e){} public void windowDeiconified(WindowEvent e){} public void windowActivated(WindowEvent e){} public void windowDeactivated(WindowEvent e){} public void windowClosing(WindowEvent e){} } Samstag, 24. November 12
13. Structural: Adapter import javax.swing.*; import java.awt.event.*; class Test extends JFrame { public Test () { setSize(200,200); setVisible(true); addWindowListener(new Closer()); } public static void main(String[] args) { new Test(); } class Closer extends WindowAdapter { public void windowClosing(WindowEvent e) { System.exit(0); } } } Samstag, 24. November 12
14. Structural: Façade Make a complex system simpler by providing a unified or general interface. -Make an entry point to your subsystems. -Minimize communication and independency -Security and performance considerations Samstag, 24. November 12
15. Structural: Façade interface General { public void accessGeneral(); } interface Special extends General { public void accessSpecial(); } interface Private extends General { public void accessPrivate(); } class GeneralInfo implements General { public void accessGeneral() { ! //... } //... } Samstag, 24. November 12
16. Structural: Façade class SpecialInfo implements Special{ public void accessSpecial() { //... } public void accessGeneral() {} //... } class PrivateInfo implements Private, Special { public void accessPrivate() { ! // ... } public void accessSpecial() { ! //... } public void accessGeneral() { ! // ... } //... } Samstag, 24. November 12
17. Structural: Façade class Connection { //... if (user is unauthorized) throw new Exception(); if (user is general) return new GeneralInfo(); if (user is special) return new SpecialInfo(); if (user is executive) return new PrivateInfo(); //... } Samstag, 24. November 12
18. Behavioral: Memento Record states -Need undo/redo features. Samstag, 24. November 12
19. Behavioral: Memento class Memento { int num; Memento(int c) { num = c; } int getNum() { return num; } } Samstag, 24. November 12
20. Behavioral: Memento class BtnDice extends JButton implements Command { Mediator med; BtnDice(ActionListener al, Mediator m) { super("Throw Dice"); addActionListener(al); med = m; med.registerDice(this); } public void execute() { med.throwit(); } } class BtnClear extends JButton implements Command { Mediator med; BtnClear(ActionListener al, Mediator m) { super("Clear"); addActionListener(al); med = m; med.registerClear(this); } public void execute() { med.clear(); } } Samstag, 24. November 12
21. Behavioral: Memento class BtnPrevious extends JButton implements Command { Mediator med; BtnPrevious(ActionListener al, Mediator m) { super("Previous"); addActionListener(al); med = m; med.registerPrevious(this); } public void execute() { med.previous(); } } class LblDisplay extends JLabel{ Mediator med; LblDisplay (Mediator m) { super("0",JLabel.CENTER); med = m; med.registerDisplay(this); setBackground(Color.white); setBorder(new EtchedBorder(Color.blue, Color.green)); Font font = new Font("Arial",Font.BOLD,40); setFont(font); } } Samstag, 24. November 12
22. Behavioral: Memento Class Mediator { BtnDice btnDice; BtnPrevious btnPrevious; BtnClear btnClear; LblDisplay show; java.util.List list, undo; boolean restart = true; int counter = 0, ct = 0; //.... Mediator() { list = new ArrayList(); undo = new ArrayList(); } void registerDice(BtnDice d) { btnDice = d; } void registerClear(BtnClear c) { btnClear = c; } void registerPrevious(BtnPrevious p) { btnPrevious = p; } Samstag, 24. November 12
23. Behavioral: Memento void registerDisplay(LblDisplay d) { show = d; } void throwit() { show.setForeground(Color.black); int num = (int)(Math.random()*6 +1); int i = counter++; list.add(i, new Integer(num)); undo.add(i, new Memento(num)); show.setText(""+num); } Samstag, 24. November 12
24. Behavioral: Memento void previous() { show.setForeground(Color.red); btnDice.setEnabled(false); if (undo.size() > 0) { ct = undo.size()-1; Memento num = (Memento)undo.get(ct); show.setText(""+num.getNum()); undo.remove(ct); } if (undo.size() == 0) show.setText("0"); } void clear() { list = new ArrayList(); undo = new ArrayList(); counter = 0; show.setText("0"); btnDice.setEnabled(true); } } Samstag, 24. November 12
25. Behavioral: Memento class MementoDemo extends JFrame implements ActionListener { Mediator med = new Mediator(); MementoDemo() { JPanel p = new JPanel(); p.add(new BtnDice(this,med)); p.add(new BtnPrevious(this,med)); p.add(new BtnClear(this,med)); JPanel dice = new JPanel(); LblDisplay lbl = new LblDisplay(med); dice.add(lbl); getContentPane().add(dice, "Center"); getContentPane().add(p, "South"); setTitle("Memento pattern example"); setDefaultCloseOperation(EXIT_ON_CLOSE); setSize(400,200); setVisible(true); } public void actionPerformed(ActionEvent ae) { Command comd = (Command)ae.getSource(); comd.execute(); } Samstag, 24. November 12
26. Behavioral: Memento public static void main(String[] args) { new MementoDemo(); } } Samstag, 24. November 12
27. Behavioral: Observer One object changes state, all of its dependents are updated automatically. -Publish or subscription -Broadcast communication Samstag, 24. November 12
28. Behavioral: Observer Samstag, 24. November 12
29. Behavioral: Observer public class EventSource extends Observable implements Runnable { public void run() { try { final InputStreamReader isr = new InputStreamReader(System.in); final BufferedReader br = new BufferedReader(isr); while (true) { String response = br.readLine(); setChanged(); notifyObservers(response); } } catch (IOException e) { e.printStackTrace(); } } } Samstag, 24. November 12
30. Behavioral: Observer public class ResponseHandler implements Observer { private String resp; public void update(Observable obj, Object arg) { if (arg instanceof String) { resp = (String) arg; System.out.println("\nReceived Response: " + resp ); } } } Samstag, 24. November 12
31. Behavioral: Observer public class MyApp { public static void main(String[] args) { System.out.println("Enter Text >"); // create an event source - reads from stdin final EventSource eventSource = new EventSource(); // create an observer final ResponseHandler responseHandler = new ResponseHandler(); // subscribe the observer to the event source eventSource.addObserver(responseHandler); // starts the event thread Thread thread = new Thread(eventSource); thread.start(); } } Samstag, 24. November 12
32. Java MVC -MVC -Business Delegate -Data Access Object Samstag, 24. November 12
33. The design patterns may just be a sign of some missing features of a given programming language (Java or C++ for instance). Peter Norvig demonstrates that 16 out of the 23 patterns in the Design Patterns book (that is primarily focused on C++) are simplified or eliminated (via direct language support) in Lisp.. Moreover, inappropriate use of patterns may unnecessarily increase complexity Samstag, 24. November 12
34. Books: -Clean Code (Clean Code: A Handbook of Agile Software Craftsmanship (Robert C. Martin)) -The Design Patterns, Java Companion (James W. Cooper) Websites: http://www.oracle.com/technetwork/java/index.html http://c2.com/cgi/wiki?PeopleProjectsAndPatterns Samstag, 24. November 12
35. Thank you ! + http://goo.gl/t4AVh @eenriquelopez http://www.neo-tech.es Samstag, 24. November 12