Object-Oriented Programming (Java), Unit 19 Kirk Scott 1.

Object-Oriented Programming (Java), Unit 19

Kirk Scott

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Panels, Adapter Classes, Anonymous Inner Classes, and Application Classes

• 19.1 Panels and Adapter Classes

• 19.2 Anonymous Inner Classes

• 19.3 Application Classes

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19.1 Panels

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Echo7

• The visible difference between Echo6 and Echo7 is that the text field is given a fixed width.

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Structural and syntactical changes in Echo7:

• The text field is given default text.• The text field is given a size.• The text field is put into its own panel in the

frame.• If the text field is not put into its own panel,

giving it a size has no effect.• The units for the width of the field do not

correspond to the number of characters of the default font that are displayed in the field.

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Structural and syntactical changes in Echo7, cont’d.:

• In Echo7 the application frame has an instance of the WindowCloser class.

• The window closer is a kind of listener.• This listener defines what is to be done

when the application is closed.• The WindowCloser class is a subclass of

the WindowAdapter class, not an implementer of the WindowListener interface.

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The Adapter classes

• An interface contains a signature for a method.• public void someMethod(parameter);• The corresponding adapter class contains an

empty implementation. • public void someMethod(parameter)• {• }

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The Adapter classes, cont’d.:

• Java provides an adapter class that corresponds to a listener class.

• If you extend the adapter class, you inherit the empty implementations of all of the other methods.

• You only need to override the methods that your class will need.

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• Unlike with an interface, you do not have to include implementations of unneeded methods.

• In this example only the windowClosing() method is overridden.

• If a listener interface like ActionListener only has one method, there is no need to use an adapter.

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The UML diagram:

• The UML diagram for Echo7 reflects all of the changes mentioned above.

• The listeners, the window closer, and the text field listener continue to be inner classes of the application frame.

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Echo7

Echo7Frame

ContentPane

JFrame

+paintComponent()+setString()

Echo7Panel

+paintComponent()+repaint()

JPanel

-has1

1

-has1

1

-has added1

1

JTextFieldGraphics

-has added1

1

-has1

1

+actionPerformed()

TextFieldListener

String

-has

1

1

WindowCloser

-has

11WindowAdapter

1

-has instance variable1

-has1

1

JPanel

-has added1

1

1


1


«interface»ActionListener 11

The UML sequence diagram:

• Java’s event handling mechanism is reminiscent of looping.

• The sequence diagram on the next overhead shows that part of the application which is conceptually the body of the loop.

• It outlines the full sequence of calls triggered by a call to actionPerformed(), the method in the text field listener.

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myListener myField myOutputPanel

actionPerformed()

getText()

inputString

setString(inputString)

setText("")

repaint()

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The code for Echo7:• import java.awt.*;• import java.awt.event.*;• import javax.swing.*;• public class Echo7• {• public static void main(String[] args)

• {• Echo7Frame myframe = new Echo7Frame();

• myframe.setVisible(true);• }• }

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• class Echo7Frame extends JFrame• {• private JTextField myField;• private Echo7Panel myOutputPanel;

• private JPanel myInputPanel;• private final int FRAMEW = 500;• private final int FRAMEH = 500;

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• public Echo7Frame()• {• setTitle("Echo7 Frame");• setSize(FRAMEW, FRAMEH);• myOutputPanel = new Echo7Panel();• myField = new JTextField("xyz", 24);• TextFieldListener myListener = new

TextFieldListener();• myField.addActionListener(myListener);• myInputPanel = new JPanel();• myInputPanel.add(myField);• Container contentPane =

getContentPane();• contentPane.add(myOutputPanel,

"Center");• contentPane.add(myInputPanel,

"North");• addWindowListener(new WindowCloser());• }

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• private class TextFieldListener implements ActionListener

• {• public void

actionPerformed(ActionEvent event)• {• String inputString =

myField.getText();•

myOutputPanel.setString(inputString);• myField.setText("");• myOutputPanel.repaint();• }• }

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• private class WindowCloser extends WindowAdapter

• {• public void windowClosing(WindowEvent event)

• {• System.exit(0);• }• }• }

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• class Echo7Panel extends JPanel• {• private String stringInQuestion = "";• private final int STRINGX = 140;• private final int STRINGY = 240;• public Echo7Panel()• {• }• public void paintComponent(Graphics g)• {• Graphics2D g2 = (Graphics2D) g;• super.paintComponent(g2);• g2.drawString(stringInQuestion, STRINGX,

STRINGY);• }• public void setString(String stringIn)• {• stringInQuestion = stringIn;• }• }

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19.2 Anonymous Inner Classes

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Echo8

• Anonymous inner classes can be used when a single instance of a class is needed and there is no reason for the class to have a name.

• Anonymous classes are cryptic.• This syntax will not be used in further example

programs.

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• It is worth hearing about anonymous inner classes because you may encounter code where they have been used.

• No screenshot is given for this example because the code still functions like the previous example.

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There is no official UML notation for anonymous inner classes:

• The inability to include anonymous inner classes as labeled elements in a diagram is a (slight) drawback.

• A small UML diagram is shown below which suggests that the Echo8Frame class has an anonymous inner class which implements the ActionListener interface.

Echo8Frame

«interface»ActionListener

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The code for Echo8:

• The code below shows the syntax for making the action listener an anonymous inner class.

• The listener is an inner class of the frame class and it is constructed inside the constructor for the frame class.

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• When constructing the listener the keyword new is followed by a call to a default constructor.

• This is followed by an opening brace and the class definition.

• The class definition contains the implementation of the actionPerformed() method.

• The class definition ends with a closing brace and this is followed by the semicolon which terminates the construction.

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• import java.awt.*;• import java.awt.event.*;• import javax.swing.*;• public class Echo8• {• public static void main(String[] args)

• {• Echo8Frame myframe = new Echo8Frame();

• myframe.setVisible(true);• }• }

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• public Echo8Frame()• {• setTitle("Echo8 Frame");• setSize(FRAMEW, FRAMEH);• myOutputPanel = new Echo8Panel();

• myField = new JTextField("xyz", 24);

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/* A call is made to construct an instance of a class that implements the interface. The definition of the class immediately follows the

constructor, and is part of the same line of code. */

• ActionListener myListener = new ActionListener()• {• public void actionPerformed(ActionEvent event)• {• String inputString = myField.getText();• myOutputPanel.setString(inputString);• myField.setText(“”);• myOutputPanel.repaint();• }• };

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• myField.addActionListener(myListener);• JPanel myInputPanel = new JPanel();• myInputPanel.add(myField);• Container contentPane =




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• private class WindowCloser extends WindowAdapter

• {• public void windowClosing(WindowEvent event)

• {• System.exit(0);• }• }• }

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• class Echo8Panel extends JPanel• {• private String stringInQuestion = "";• private final int STRINGX = 140;• private final int STRINGY = 240;• public Echo8Panel()• {• }• public void paintComponent(Graphics g)• {• Graphics2D g2 = (Graphics2D) g;• super.paintComponent(g2);• g2.drawString(stringInQuestion, STRINGX,

STRINGY);• }• public void setString(String stringIn)• {• stringInQuestion = stringIn;• }• }

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19.3 Application Classes

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Echo9

• Echo9 introduces a cup class.• A cup contains a seed count and it also has

attributes that describe it as a rectangle with x and y coordinates in the frame.

• The application accepts an integer value in the text field which is used to set the seedCount of the cup.

• When the seedCount is set, the application has to be repainted in order to reflect the change.

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The Echo9 screenshot:

• In the screenshot a cup is represented by a rectangle.

• The value of the seedCount variable is given using Unicode.

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• The UML structure diagram differs from the previous one only by the presence of the Cup class instead of a String in the output panel.

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Echo9

Echo9Frame

ContentPane

JFrame

+paintComponent()+setCup()

Echo9Panel

+paintComponent()+repaint()

JPanel

-has1

1

-has1

1

-has added1

1

JTextFieldGraphics

-has added1

1

-has1

1

+actionPerformed()

TextFieldListener

+setCupValue()+drawCup()

Cup

-has

1

1

WindowCloser

-has

11WindowAdapter

1


-has1

1

JPanel

-has added

1

1

1


1


«interface»ActionListener 37

The UML Static Structure Diagram:

• You can identify an input side and an output side of the application.

• Actions which take in a value and change the state of the application are input.

• Actions that are triggered by the call to repaint() and follow it, which cause the state of the application to be shown, are output.

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More on the UML Static Structure Diagram:

• The text field listener has access to the instance of the Echo9Panel, the output panel, which is an instance variable of the frame.

• When a seed count is entered into the text field, the listener calls the setCup() method on the panel, passing in the count.

• The setCup() method calls the setSeedCount() method on the cup belonging to the panel, passing in the count.

• The listener then calls repaint() on the panel.

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UML Sequence Diagrams for the Application

• The first sequence diagram shows the actions that occur on the input side of the application:

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myListener myField myOutputPanel

actionPerformed()

getText()

inputString

setCup(Integer.parseInt(inputString))

setText("")

repaint()

myCup

setSeedCount()

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• The second sequence diagram shows the actions that occur on the output side of the application:

• In other words, this is the sequence of method calls triggered by the call to repaint().

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• The call to repaint() triggers a call to the paintComponent() method of Echo9Panel.

• Inside paintComponent() a call is made to drawCup().

• The graphics parameter is passed from paintComponent() to drawCup(), where methods to draw the rectangle and display the seedCount of the cup are called on the graphics parameter.

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myOutputPanel myCup g2

repaint()

drawCup(g2)

draw(Rectangle...)

drawString(Integer...)

update()

paintComponent()

super.paintComponent()

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The code for Echo9:

• Notice these things in the code

• There is now a cup class.

• The cup is represented by an instance of the Rectangle class.

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• Instances of the Rectangle are constructed when the cup is displayed. They are not saved as instance variables.

• Whether or not things like the rectangle are saved as instance variables or constructed at display time becomes an important issue in future versions of the application

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• import java.awt.*;• import java.awt.event.*;• import javax.swing.*;• import java.awt.Graphics2D;• import java.awt.Rectangle;• public class Echo9• {• public static void main(String[] args)• {• Echo9Frame myframe = new Echo9Frame();• myframe.setVisible(true);• }• }

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• public Echo9Frame()• {• setTitle("Echo9 Frame");• setSize(FRAMEW, FRAMEH);• myOutputPanel = new Echo9Panel();• myField = new JTextField("4", 24);• TextFieldListener myListener = new

TextFieldListener();• myField.addActionListener(myListener);• JPanel myInputPanel = new JPanel();• myInputPanel.add(myField);• Container contentPane =




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• private class TextFieldListener implements ActionListener

• {• public void actionPerformed(ActionEvent event)• {• String inputString = myField.getText();•

myOutputPanel.setCup(Integer.parseInt(inputString));• myField.setText("");• myOutputPanel.repaint();• }• }

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• private class WindowCloser extends WindowAdapter• {• public void windowClosing(WindowEvent event)• {• System.exit(0);• }• }• }

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• class Echo9Panel extends JPanel• {• private Echo9Cup myCup;• public Echo9Panel()• {• myCup = new Echo9Cup(0, 200, 200, 40, 40);• }• public void paintComponent(Graphics g)• {• Graphics2D g2 = (Graphics2D) g;• super.paintComponent(g2);• myCup.drawCup(g2);• }• public void setCup(int inValue)• {• myCup.setSeedCount(inValue);• }• }

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• class Echo9Cup• {• private int seedCount;• private int x;• private int y;• private int w;• private int h;• private int textX;• private int textY;

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• public Echo9Cup(int inValue, int cupX, int cupY, int cupW, int cupH)

• {• seedCount = inValue;• x = cupX;• y = cupY;• w = cupW;• h = cupH;• textX = cupX + (int) (.25 * cupW);• textY = cupY + (int) (.6 * cupH);• }

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• public void setSeedCount(int inValue)• {• seedCount = inValue;• }• public void drawCup(Graphics2D g2)• {• g2.draw(new Rectangle(x, y, w, h));•

g2.drawString(Integer.toString(seedCount), textX, textY);

• }• }

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The End

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Object-Oriented Programming (Java), Unit 19 Kirk Scott 1.

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