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9 Creating GUI

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9 Creating GUI Powered By Docstoc
					Creating User Interfaces




                           1
                 Motivations
A graphical user interface (GUI) makes a system
user-friendly and easy to use. Creating a GUI
requires creativity and knowledge of how GUI
components work. Since the GUI components in
Java are very flexible and versatile, you can create
a wide assortment of useful user interfaces.

Previous chapters briefly introduced several GUI
components. This chapter introduces the
frequently used GUI components in detail.
                                                 2
                             Objectives
   To create graphical user interfaces with various user-interface components:
    JButton, JCheckBox, JRadioButton, JLabel, JTextField, JTextArea,
    JComboBox, JList, JScrollBar, and JSlider.
   To create listeners for various types of events.
   To explore JButton
   To explore JCheckBox
   To explore JRadioButton
   To explore JLabel
   To explore JTextField
   To explore JTextArea
   To explore JComboBox
   To explore JList
   To explore JScrollBar
   To explore JSlider
   To display multiple windows in an application.


                                                                          3
 Components Covered in the Chapter
Introducesthe frequently used GUI components
Uses borders and icons

                                                       JButton
Component   Container   JComponent   AbstractButton                          JCheckBox
                                                       JToggleButton
                                                                             JRadioButton
                                      JLabel
                                                       JTextArea

                                      JTextComponent
                                                       JTextField      JPasswordField
                                      JComboBox

                                      JList

                                      JScrollBar


                                      JSlider




                                                                                    4
                     Buttons
A button is a component that triggers an action event
when clicked. Swing provides regular buttons,
toggle buttons, check box buttons, and radio buttons.
The common features of these buttons are
generalized in javax.swing.AbstractButton.




                                                   5
                                  AbstractButton
  javax.swing.JComponent
                                           The get and set methods for these data fields are provided in
                                           the class, but omitted in the UML diagram for brevity.
 javax.swing.AbstractButton
-actionCommand: String             The action command of this button.
-text: String                      The button’s text (i.e., the text label on the button).
-icon: javax.swing.Icon            The button’s default icon. This icon is also used as the "pressed" and
                                     "disabled" icon if there is no explicitly set pressed icon.
-pressedIcon: javax.swing.Icon     The pressed icon (displayed when the button is pressed).
-rolloverIcon: javax.swing.Icon    The rollover icon (displayed when the mouse is over the button).
-mnemonic: int                     The mnemonic key value of this button. You can select the button by
                                    pressing the ALT key and the mnemonic key at the same time.
-horizontalAlignment: int          The horizontal alignment of the icon and text (default: CENTER).
-horizontalTextPosition: int       The horizontal text position relative to the icon (default: RIGHT).
-verticalAlignment: int            The vertical alignment of the icon and text (default: CENTER).
-verticalTextPosition: int         The vertical text position relative to the icon (default: CENTER).
-borderPainted: boolean            Indicates whether the border of the button is painted. By default, a regular
                                     button’s border is painted, but the borders for a check box and a radio
                                     button is not painted.
-iconTextGap: int                  The gap between the text and the icon on the button (JDK 1.4).
-selected(): boolean               The state of the button. True if the check box or radio button is selected,
                                     false if it's not.
                                                                                                            6
                                 JButton
JButton inherits AbstractButton and provides several
constructors to create buttons.

    javax.swing.AbstractButton

        javax.swing.JButton
+JButton()                           Creates a default button with no text and icon.
+JButton(icon: javax.swing.Icon)     Creates a button with an icon.
+JButton(text: String)               Creates a button with text.
+JButton(text: String, icon: Icon)   Creates a button with text and an icon.




                                                                                 7
         JButton Constructors
The following are JButton constructors:
JButton()
JButton(String text)
JButton(String text, Icon icon)
JButton(Icon icon)




                                          8
         JButton Properties
 text

 icon

 mnemonic

 horizontalAlignment

 verticalAlignment

 horizontalTextPosition

 verticalTextPosition

 iconTextGap
                              9
       Default Icons, Pressed Icon, and
                Rollover Icon
  A regular button has a default icon, pressed icon,
  and rollover icon. Normally, you use the default
  icon. All other icons are for special effects. A
  pressed icon is displayed when a button is pressed
  and a rollover icon is displayed when the mouse
  is over the button but not pressed.




(A) Default icon   (B) Pressed icon   (C) Rollover icon

                                                      10
   Demo


TestButtonIcons

     Run




                  11
          Horizontal Alignments
Horizontal alignment specifies how the icon and
text are placed horizontally on a button. You can set
the horizontal alignment using one of the five
constants: LEADING, LEFT, CENTER, RIGHT,
TRAILING. At present, LEADING and LEFT are
the same and TRAILING and RIGHT are the same.
Future implementation may distinguish them. The
default horizontal alignment is
SwingConstants.TRAILING.




                                                 12
           Vertical Alignments
Vertical alignment specifies how the icon and
text are placed vertically on a button. You can
set the vertical alignment using one of the
three constants: TOP, CENTER, BOTTOM.
The default vertical alignment is
SwingConstants.CENTER.




                                           13
        Horizontal Text Positions
Horizontal text position specifies the
horizontal position of the text relative to the
icon. You can set the horizontal text position
using one of the five constants: LEADING,
LEFT, CENTER, RIGHT, TRAILING. The
default horizontal text position is
SwingConstants.RIGHT.




                                             14
          Vertical Text Positions
Vertical text position specifies the vertical
position of the text relative to the icon. You
can set the vertical text position using one of
the three constants: TOP, CENTER. The
default vertical text position is
SwingConstants.CENTER.




                                             15
           Example: Using Buttons
Write a program that displays a
                                  MessagePanel
message on a panel and uses
two buttons, <= and =>, to move   ButtonDemo
the message on the panel to the
left or right.                        Run



             MessagePanel




           JButton   JButton




                                                 16
                                       JCheckBox
JCheckBox inherits all the properties such as text, icon,
mnemonic, verticalAlignment, horizontalAlignment,
horizontalTextPosition, verticalTextPosition, and selected
from AbstractButton, and provides several constructors to
create check boxes.
   javax.swing.AbstractButton

   javax.swing.JToggleButton

     javax.swing.JCheckBox
+JCheckBox()                           Creates a default check box button with no text and icon.
+JCheckBox(text: String)               Creates a check box with text.
+JCheckBox(text: String, selected:     Creates a check box with text and specifies whether the check box is
 boolean)                               initially selected.
+JCheckBox(icon: Icon)                 Creates a checkbox with an icon.
+JCheckBox(text: String, icon: Icon)   Creates a checkbox with text and an icon.
+JCheckBox(text: String, icon: Icon,   Creates a check box with text and an icon, and specifies whether the check
 selected: boolean)                     box is initially selected.

                                                                                                              17
    Example: Using Check Boxes
Add three check boxes named
Centered, Bold, and Italic
into the ButtonDemo example
to let the user specify whether
the message is centered, bold,
or italic.
                                    ButtonDemo



                                   CheckBoxDemo




        CheckBoxDemo              Run
                                                  18
                                 JRadioButton
Radio buttons are variations of check boxes. They are
often used in the group, where only one button is
checked at a time.
    javax.swing.AbstractButton

    javax.swing.JToggleButton

    javax.swing.JRadioButton
+JRadioButton()                           Creates a default radio button with no text and icon.
+JRadioButton(text: String)               Creates a radio button with text.
+JRadioButton(text: String, selected:     Creates a radio button with text and specifies whether the radio button is
 boolean)                                  initially selected.
+JRadioButton(icon: Icon)                 Creates a radio button with an icon.
+JRadioButton(text: String, icon: Icon)   Creates a radio button with text and an icon.
+JRadioButton(text: String, icon: Icon,   Creates a radio button with text and an icon, and specifies whether the radio
 selected: boolean)                        button is initially selected.



                                                                                                                  19
     Grouping Radio Buttons

ButtonGroup btg = new ButtonGroup();
btg.add(jrb1);
btg.add(jrb2);




                                       20
   Example: Using Radio Buttons
Add three radio buttons
named Red, Green, and
Blue into the preceding
example to let the user
choose the color of the
message.                    ButtonDemo



                           CheckBoxDemo



                          RadioButtonDemo




        RadioButtonDemo     Run
                                            21
                                             JLabel
A label is a display area for a short text, an image, or both.
      javax.swing.JComponent
                                                 The get and set methods for these data fields are provided in
                                                 the class, but omitted in the UML diagram for brevity.
          javax.swing.JLabel
  -text: String                            The label’s text.
  -icon: javax.swing.Icon                  The label’s image icon.
  -horizontalAlignment: int                The horizontal alignment of the text and icon on the label.
  -horizontalTextPosition: int             The horizontal text position relative to the icon on the label.
  -verticalAlignment: int                  The vertical alignment of the text and icon on the label.
  -verticalTextPosition: int               The vertical text position relative to the icon on the label.
  -iconTextGap: int                        The gap between the text and the icon on the label (JDK 1.4).
  +JLabel()                                Creates a default label with no text and icon.
  +JLabel(icon: javax.swing.Icon)          Creates a label with an icon.
  +JLabel(icon: Icon, hAlignment: int)     Creates a label with an icon and the specified horizontal alignment.
  +JLabel(text: String)                    Creates a label with text.
  +JLabel(text: String, icon: Icon,        Creates a label with text, an icon, and the specified horizontal alignment.
    hAlignment: int)
  +JLabel(text: String, hAlignment: int)   Creates a label with text and the specified horizontal alignment.

                                                                                                                  22
               JLabel Constructors
The constructors for labels are as follows:
JLabel()
JLabel(String text, int horizontalAlignment)
JLabel(String text)
JLabel(Icon icon)
JLabel(Icon icon, int horizontalAlignment)
JLabel(String text, Icon icon, int
horizontalAlignment)



                                               23
        JLabel Properties
JLabel inherits all the properties from
JComponent and has many properties
similar to the ones in JButton, such as
text, icon, horizontalAlignment,
verticalAlignment,
horizontalTextPosition,
verticalTextPosition, and iconTextGap.




                                          24
                       Using Labels
// Create an image icon from image file
ImageIcon icon = new ImageIcon("image/grapes.gif");

// Create a label with text, an icon,
// with centered horizontal alignment
JLabel jlbl = new JLabel("Grapes", icon,
SwingConstants.CENTER);

// Set label's text alignment and gap between text and icon
jlbl.setHorizontalTextPosition(SwingConstants.CENTER);
jlbl.setVerticalTextPosition(SwingConstants.BOTTOM);
jlbl.setIconTextGap(5);


                                                              25
                                      JTextField
A text field is an input area where the user can type in
characters. Text fields are useful in that they enable the user to
enter in variable data (such as a name or a description).

                                              The get and set methods for these data fields are provided in
                                              the class, but omitted in the UML diagram for brevity.
    javax.swing.text.JTextComponent
  -text: String                             The text contained in this text component.
  -editable: boolean                        Indicates whether this text component is editable (default: true).


           javax.swing.JTextField
  -columns: int                             The number of columns in this text field.
  -horizontalAlignment: int                 The horizontal alignment of this text field (default: LEFT).
  +JTextField()                             Creates a default empty text field with number of columns set to 0.
  +JTextField(column: int)                  Creates an empty text field with specified number of columns.
  +JTextField(text: String)                 Creates a text field initialized with the specified text.
  +JTextField(text: String, columns: int)   Creates a text field initialized with the specified text and columns.



                                                                                                                 26
      JTextField Constructors
   JTextField(int columns)
    Creates an empty text field with the specified
    number of columns.
   JTextField(String text)
    Creates a text field initialized with the specified text.
   JTextField(String text, int columns)
    Creates a text field initialized with the
    specified text and the column size.



                                                                27
    JTextField Properties
 text

 horizontalAlignment

 editable

 columns




                            28
           JTextField Methods
   getText()
    Returns the string from the text field.
   setText(String text)
    Puts the given string in the text field.
   setEditable(boolean editable)
    Enables or disables the text field to be edited. By default,
    editable is true.

   setColumns(int)
    Sets the number of columns in this text field.
    The length of the text field is changeable.

                                                                   29
          Example: Using Text Fields
Add a text field to the
preceding example to
let the user set a new
message.


 JFrame      ButtonDemo   CheckBoxDemo   RadioButtonDemo   TextFieldDemo




                   TextFieldDemo                     Run


                                                               30
                                             JTextArea
If you want to let the user enter multiple lines of text, you cannot use
text fields unless you create several of them. The solution is to use
JTextArea, which enables the user to enter multiple lines of text.

     javax.swing.text.JTextComponent                        The get and set methods for these data fields are provided in
                                                            the class, but omitted in the UML diagram for brevity.
               javax.swing.JTextArea
  -columns: int                                     The number of columns in this text area.
  -rows: int                                        The number of rows in this text area.
  -tabSize: int                                     The number of characters used to expand tabs (default: 8).
  -lineWrap: boolean                                Indicates whether the line in the text area is automatically wrapped (default:
                                                     false).
  -wrapStyleWord: boolean                           Indicates whether the line is wrapped on words or characters (default: false).
  +JTextArea()                                      Creates a default empty text area.
  +JTextArea(rows: int, columns: int)               Creates an empty text area with the specified number of rows and columns.
  +JTextArea(text: String)                          Creates a new text area with the specified text displayed.
  +JTextArea(text: String, rows: int, columns: int) Creates a new text area with the specified text and number of rows and columns.
  +append(s: String): void                          Appends the string to text in the text area.
  +insert(s: String, pos: int): void                Inserts string s in the specified position in the text area.
  +replaceRange(s: String, start: int, end: int):   Replaces partial text in the range from position start to end with string s.
    void
  +getLineCount(): int                              Returns the actual number of lines contained in the text area.

                                                                                                                                   31
        JTextArea Constructors
   JTextArea(int rows, int columns)
    Creates a text area with the specified number of
    rows and columns.

   JTextArea(String s, int rows, int
    columns)
    Creates a text area with the initial text and
    the number of rows and columns specified.




                                                       32
    JTextArea Properties
 text
 editable
 columns
 lineWrap
 wrapStyleWord
 rows
 lineCount
 tabSize
                           33
    Example: Using Text Areas
 This example gives a program that displays
 an image in a label, a title in a label, and a
 text in a text area.

                 JPanel                                     JFrame
         -char token                                   -char token

        +getToken                              1   1   +getToken
              DescriptionPanel                         TextAreaDemo
        +setToken                                      +setToken
        +paintComponet                                 +paintComponet
     -jlblImage: JLabel
        +mouseClicked                                  +mouseClicked
     -jtaTextDescription: JTextArea

     +setImageIcon(icon: ImageIcon): void
     +setTitle(title: String): void
     +setTextDescription(text: String): void
     +getMinimumSize(): Dimension




                                                                        34
            Example, cont.




DescriptionPanel   TextAreaDemo   Run

                                    35
                                     JComboBox
A combo box is a simple list of items from which the user can
choose. It performs basically the same function as a list, but
can get only one value.
       javax.swing.JComponent

       javax.swing.JComboBox
    +JComboBox()                           Creates a default empty combo box.
    +JComboBox(items: Object[])            Creates a combo box that contains the elements in the specified array.
    +addItem(item: Object): void           Adds an item to the combo box.
    +getItemAt(index: int): Object         Returns the item at the specified index.
    +getItemCount(): int                   Returns the number of items in the combo box.
    +getSelectedIndex(): int               Returns the index of the selected item.
    +setSelectedIndex(index: int): void    Sets the selected index in the combo box.
    +getSelectedItem(): Object             Returns the selected item.
    +setSelectedItem(item: Object): void   Sets the selected item in the combo box.
    +removeItem(anObject: Object): void Removes an item from the item list.
    +removeItemAt(anIndex: int): void   Removes the item at the specified index in the combo box.
    +removeAllItems(): void                Removes all items in the combo box.


                                                                                                            36
      JComboBox Methods
To add an item to a JComboBox jcbo, use
jcbo.addItem(Object item)

To get an item from JComboBox jcbo, use
jcbo.getItem()




                                          37
                Using the
   itemStateChanged Handler
  When a choice is checked or unchecked,
  itemStateChanged() for ItemEvent is
  invoked as well as the actionPerformed()
  handler for ActionEvent.
public void itemStateChanged(ItemEvent e) {
  // Make sure the source is a combo box
  if (e.getSource() instanceof JComboBox)
    String s = (String)e.getItem();
}

                                             38
  Example: Using Combo Boxes
This example lets
users view an
image and a
description of a
country's flag by
selecting the
country from a
combo box.

       ComboBoxDemo   Run

                            39
                                                   JList
A list is a component that performs basically the same function as a combo
box, but it enables the user to choose a single value or multiple values.
        javax.swing.JComponent

              javax.swing.JList
   +JList()                                    Creates a default empty list.
   +JList(items: Object[])                     Creates a list that contains the elements in the specified array.
   +getSelectedIndex(): int                    Returns the index of the first selected item.
   +setSelectedIndex(index: int): void         Selects the cell at the specified index.
   +getSelectedIndices(): int[]                Returns an array of all of the selected indices in increasing order.
   +setSelectedIndices(indices: int[]): void Selects the cells at the specified indices.
   +getSelectedValue(): Object               Returns the first selected item in the list.
   +getSelectedValues(): Object[]              Returns an array of the values for the selected cells in increasing index order.
   +getVisibleRowCount(): int                  Returns the number of visible rows displayed without a scrollbar. (default: 8)
   +setVisibleRowCount(count: int): void       Sets the preferred number of visible rows displayed without a scrollbar.
   +getSelectionBackground(): Color            Returns the background color of the selected cells.
   +setSelectionBackground(c: Color): void Sets the background color of the selected cells.
   +getSelectionForeground(): Color        Returns the foreground color of the selected cells.
   +setSelectionForeground(c: Color): void Sets the foreground color of the selected cells.
   +getSelectionMode(): int                Returns the selection mode for the list.
   +setSelectionMode(selectionMode: int): Sets the selection mode for the list.
                                                                                                                            40
             JList Constructors
   JList()

    Creates an empty list.

   JList(Object[] stringItems)
    Creates a new list initialized with items.




                                                 41
      JList Properties
 selectedIndexd

 selectedIndices

 selectedValue

 selectedValues

 selectionMode

 visibleRowCount

                         42
         Example: Using Lists
This example gives
a program that lets
users select
countries in a list
and display the flags
of the selected
countries in the
labels.


             ListDemo    Run
                                43
                                        JScrollBar
A scroll bar is a control that enables the user to select from a range of values. The
scrollbar appears in two styles: horizontal and vertical.
               javax.swing.JComponent
                                                        The get and set methods for these data fields are provided in
                                                        the class, but omitted in the UML diagram for brevity.
                javax.swing.JScrollBar
             -orientation: int                     Specifies horizontal or vertical style, default is horizontal.
             -maximum: int                         Specifies the maximum value the scroll bar represents when the bubble
                                                     reaches the right end of the scroll bar for horizontal style or the
                                                     bottom of the scroll bar for vertical style.
             -minimum: int                         Specifies the minimum value the scroll bar represents when the bubble
                                                     reaches the left end of the scroll bar for horizontal style or the top of
                                                     the scroll bar for vertical style.
             -visibleAmount: int                   Specifies the relative width of the scroll bar's bubble. The actual width
                                                     appearing on the screen is determined by the maximum value and the
                                                     value of visibleAmount.
             -value: int                           Represents the current value of the scroll bar.
             -blockIncrement: int                  Specifies value added (subtracted) when the user activates the block-
                                                     increment (decrement) area of the scroll bar, as shown in Figure
                                                     13.30.
             -unitIncrement: int                   Specifies the value added (subtracted) when the user activates the unit-
                                                     increment (decrement) area of the scroll bar, as shown in Figure
                                                     13.30.

             +JScrollBar()                         Creates a default vertical scroll bar.
             +JScrollBar(orientation: int)         Creates a scroll bar with the specified orientation.
             +JScrollBar(orientation: int, value: Creates a scrollbar with the specified orientation, value, extent,
               int, extent: int, min: int, max: int) minimum, and maximum.


                                                                                                                                 44
        Scroll Bar Properties
Minimal value                                 Maximal value

         Block decrement            Block increment




                           Bubble
 Unit decrement                           Unit increment



                                                              45
        Example: Using Scrollbars
This example uses
horizontal and vertical
scrollbars to control a
message displayed on a
panel. The horizontal
scrollbar is used to move
the message to the left or
the right, and the vertical
scrollbar to move it up and
down.


           ScrollBarDemo      Run
                                    46
                                              JSlider
JSlider is similar to JScrollBar, but JSlider has more
properties and can appear in many forms.
            javax.swing.JComponent
                                                        The get and set methods for these data fields are provided in
                                                        the class, but omitted in the UML diagram for brevity.
                javax.swing.JSlider
       -maximum: int                               The maximum value represented by the slider (default: 100).
       -minimum: int                               The minimum value represented by the slider (default: 0).
       -value: int                                 The current value represented by the slider.
       -orientation: int                           The orientation of the slider (default: JSlider.HORIZONTAL).
       -paintLabels: boolean                       True if the labels are painted at tick marks (default: false).
       -paintTicks: boolean                        True if the ticks are painted on the slider (default: false).
       -paintTrack: boolean                        True if the track is painted on the slider (default: true).
       -majorTickSpacing: int                      The number of units between major ticks (default: 0).
       -minorTickSpacing: int                      The number of units between minor ticks (default: 0).
       -inverted: boolean                          True to reverse the value-range, and false to put the value range in the
                                                    normal order (default: false).
       +JSlider()                                  Creates a default horizontal slider.
       +JSlider(min: int, max: int)                Creates a horizontal slider using the specified min and max.
       +JSlider(min: int, max: int, value: int)    Creates a horizontal slider using the specified min, max, and value.
       +JSlider(orientation: int)                  Creates a slider with the specified orientation.
       +JSlider(orientation: int, min: int, max:   Creates a slider with the specified orientation, min, max, and value.
         int, value: int)

                                                                                                                              47
           Example: Using Sliders
Rewrite the preceding
program using the sliders
to control a message
displayed on a panel
instead of using scroll
bars.




             SliderDemo       Run
                                    48
  Creating Multiple Windows
The following slides show step-by-step how to
create an additional window from an application
or applet.




                                             49
   Creating Additional Windows, Step 1

Step 1: Create a subclass of JFrame (called a
SubFrame) that tells the new window what
to do. For example, all the GUI application
programs extend JFrame and are subclasses
of JFrame.




                                                50
   Creating Additional Windows, Step 2

Step 2: Create an instance of SubFrame in the
application or applet.

Example:
SubFrame subFrame = new
  SubFrame("SubFrame Title");




                                                51
   Creating Additional Windows, Step 3

Step 3: Create a JButton for activating the
subFrame.
add(new JButton("Activate SubFrame"));




                                              52
         Creating Additional Windows, Step 4

Step 4: Override the actionPerformed()
method as follows:
public actionPerformed(ActionEvent e) {
  String actionCommand = e.getActionCommand();
  if (e.target instanceof Button) {
    if ("Activate SubFrame".equals(actionCommand)) {
      subFrame.setVisible(true);
    }
  }
}




                                                       53
    Example: Creating Multiple
           Windows
 This example creates a main window with a
 text area in the scroll pane, and a button
 named "Show Histogram." When the user
 clicks the button, a new window appears
 that displays a histogram to show the
 occurrence of the letters in the text area.




                                           54
          Example, cont.




MultipleWindowsDemo        Run

     Histogram

                                 55

				
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