Object–oriented programming Graphic interfaces
Marcin Młotkowski
11th April, 2012
Programmer’s life Swing Traps and solutions
Outline
1
Programmer’s life
2
Swing Windows and widgets Event handling
3
Traps and solutions Programmer’s life, part 2 Model–View–Controller
Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
1st stage
Specification Implement a system for libraries.
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Object–oriented programming
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Programmer’s life Swing Traps and solutions
A part of implementation public class Book { private String title; private String author; private int edition; public Book(String t, String a, int w) { this.title = t; this.author = a; this.edition = w; } public String toString() { return "ook " + this.title + " " + this.author; } } Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
2nd stage
Extended specification "I need an editor in window!"
Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
Java implementation public class Book { private String title; private String author; private int edition; public Book(String t, String a, int w) { ... } public String toString() { ... } public void Edit() { ... } }
Marcin Młotkowski
Object–oriented programming
6 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Outline
1
Programmer’s life
2
Swing Windows and widgets Event handling
3
Traps and solutions Programmer’s life, part 2 Model–View–Controller
Marcin Młotkowski
Object–oriented programming
7 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Introduction to Swing
Overview better version of AWT (Abstract Window Toolkit); independence from view and operating system; support for internationalization. Heavy usage of classes, objects, and inheritance.
Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Components of Swing
"Visual" elements Windows, widgets, menus. "Invisible" elements Events, listeners.
Marcin Młotkowski
Object–oriented programming
9 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Where is Swing?
import javax.swing.*; import java.awt.*; import java.awt.event.*;
Marcin Młotkowski
Object–oriented programming
10 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Class hierarchy javax.swing.* JComponent
JLabel
Frame
JTextComponent JFrame
JTextField
Marcin Młotkowski
Object–oriented programming
11 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Rapid solution
Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Main window
JFrame frame = new JFrame("Edit book"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Marcin Młotkowski
Object–oriented programming
13 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Main window
JFrame frame = new JFrame("Edit book"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); Container container = frame.getContentPane(); GridLayout layout = new GridLayout(4, 2); container.setLayout(layout);
Marcin Młotkowski
Object–oriented programming
13 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Author
JLabel author_label = new JLabel("Author"); container.add(author_label); JTextField author = new JTextField(this.author, 40); container.add(author);
Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Title
JLabel title_label = new JLabel("Title"); container.add(title_label); JTextField title = new JTextField(this.title, 40); container.add(title);
Marcin Młotkowski
Object–oriented programming
15 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Edition
JLabel wydanie_label = new JLabel("Edition"); container.add(wydanie_label); JTextField edition = new JTextField(Integer.toString(this.edition), 40); container.add(edition);
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Object–oriented programming
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Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Save button
JButton b = new JButton("Save"); b.addActionListener(this); container.add(b);
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Object–oriented programming
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Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
End of window building
frame.pack(); frame.setVisible(true);
Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Clicking response
public class Book implements ActionListener { public void actionPerformed(ActionEvent e) { // Eg. take data from widget: JTextfield.getText();
} public void Edit() { b.addActionListener(this); } }
Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Result
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Object–oriented programming
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Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Events
Event Clicking a mouse button, pressing a key, timeout, closing a window etc. Widget A widget connected to the event, eg. key pressed. Event handling A method executed after an event.
Marcin Młotkowski
Object–oriented programming
21 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Event subscription in Swing
A widget which "receives an event" Each widget has a list of classes, which implements an interface ActionListener. After event occurrence, each listener is notified of the event. Listener Must implement a method actionPerformed(ActionEvent), which is invoked after an event.
Marcin Młotkowski
Object–oriented programming
22 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Implementation public class Book implements ActionListener { public void actionPerformed(ActionEvent e) { ... } public void Edit() { ... JButton b = new JButton("Save"); b.addActionListener(this); ... } }
Marcin Młotkowski
Object–oriented programming
23 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Listeners, summary
The object may register any number of Listeners; each listener is notified of the event; Listener implements interface EventListener and derivates, including ActionListener.
Marcin Młotkowski
Object–oriented programming
24 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Listener implementation, 1st approach
public class Book implements ActionListener { b.addActionListener(this); }
Marcin Młotkowski
Object–oriented programming
25 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Listener implementation, 2nd approach
public class Book { class MyListener implements ActionListener { public void actionPerformed(ActionEvent e) { ... } } ... b.addActionListener(new MyListener()); ... }
Marcin Młotkowski
Object–oriented programming
26 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Listener implementation, 3rd approach
b.ActionListener( new ActionListener() { public void actionPerformed(ActionEvent evt) { ... } } );
Marcin Młotkowski
Object–oriented programming
27 / 41
Programmer’s life Swing Traps and solutions
Windows and widgets Event handling
Anonymous class
could be defined "in the fly"; no need to think of a name of the class; anonymous class has an access to the fields of the "larger" class.
Marcin Młotkowski
Object–oriented programming
28 / 41
Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
Outline
1
Programmer’s life
2
Swing Windows and widgets Event handling
3
Traps and solutions Programmer’s life, part 2 Model–View–Controller
Marcin Młotkowski
Object–oriented programming
29 / 41
Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
Extension of our application
" I need it on my mobile phone, palmtop etc"
Marcin Młotkowski
Object–oriented programming
30 / 41
Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
Extension of our application
" I need it on my mobile phone, palmtop etc" Implementation public class Book { public void Edit() { ... } public void EditPhoneVersion() { ... } public void EditPalmtopVersion() { ... } }
Marcin Młotkowski
Object–oriented programming
30 / 41
Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
Result
"core" implementation of Book: 15 lines; implementation of edition (Swing only): 40 lines
Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
Is Book a good name?
Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
What is inside the class Book?
implementation a notion of a book; implementation of the interaction with a user
Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
Design principle
Single responsibility principle Each class/object should have a single responsibility.
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Object–oriented programming
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Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
Introduction
Design pattern MVC: Model–View–Controller one of the first design patterns; designed for GUI implementations.
Marcin Młotkowski
Object–oriented programming
35 / 41
Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
Interaction with environment
Book
Edit book
Marcin Młotkowski
- author: String - title: String - edition: int
Object–oriented programming
36 / 41
Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
MVC
Model Data with relations among data View Data view (screen, printer, html) Controller "Something" what modifies a state of Model (eg. buttons).
Marcin Młotkowski
Object–oriented programming
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Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
Cooperations
A controller has a reference to a Model and as a reaction to user action (pressing a key), call methods of Model which modifies a state of Model. View (or Views) listen changes of Model and update thier views.
Marcin Młotkowski
Object–oriented programming
38 / 41
Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
MVC in Swing
Book
Edit book
Marcin Młotkowski
- author: String - title: String - edition: int
Object–oriented programming
39 / 41
Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
Code improvement
Split the previous class into two classes: public class Book { ... }
public class BookSwing { public BookSwing(Book k) { ... } }
Marcin Młotkowski
Object–oriented programming
40 / 41
Programmer’s life Swing Traps and solutions
Programmer’s life, part 2 Model–View–Controller
Summary
Splitting class into more classes (using responsibility) results in more natural components. MVC allow independent implementation of a model ant its graphic interfaces.
Marcin Młotkowski
Object–oriented programming
41 / 41
