Transcript Chapter 17

Chapter 17
Creating User Interfaces
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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.
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Objectives













To create graphical user interfaces with various user-interface components:
JButton, JCheckBox, JRadioButton, JLabel, JTextField, JTextArea,
JComboBox, JList, JScrollBar, and JSlider (§§17.2–17.11).
To create listeners for various types of events (§§17.2–17.11).
To explore JButton (§17.2)
To explore JCheckBox (§17.3)
To explore JRadioButton (§17.4)
To explore JLabel (§17.5)
To explore JTextField (§17.6)
To explore JTextArea (§17.7)
To explore JComboBox (§17.8)
To explore JList (§17.9)
To explore JScrollBar (§17.10)
To explore JSlider (§17.11)
To display multiple windows in an application (§17.12).
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Components Covered in the Chapter
Introduces
the 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
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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.
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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.
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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.
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JButton Constructors
The following are JButton constructors:
JButton()
JButton(String text)
JButton(String text, Icon icon)
JButton(Icon icon)
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JButton Properties
 text
 icon
 mnemonic
 horizontalAlignment
 verticalAlignment
 horizontalTextPosition
 verticalTextPosition
 iconTextGap
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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
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Demo
TestButtonIcons
Run
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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.
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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.
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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.
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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.
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Example: Using Buttons
Write a program that displays a
message on a panel and uses
two buttons, <= and =>, to move
the message on the panel to the
left or right.
ButtonDemo
Run
MessagePanel
JButton
JButton
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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:
boolean)
Creates a check box with text and specifies whether the check box is
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,
selected: boolean)
Creates a check box with text and an icon, and specifies whether the check
box is initially selected.
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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
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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:
boolean)
Creates a radio button with text and specifies whether the radio button is
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,
selected: boolean)
Creates a radio button with text and an icon, and specifies whether the radio
button is initially selected.
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Grouping Radio Buttons
ButtonGroup btg = new ButtonGroup();
btg.add(jrb1);
btg.add(jrb2);
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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
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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,
hAlignment: int)
Creates a label with text, an icon, and the specified horizontal alignment.
+JLabel(text: String, hAlignment: int)
Creates a label with text and the specified horizontal alignment.
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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)
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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.
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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);
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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).
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.
-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.
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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.
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JTextField Properties
 text
 horizontalAlignment
 editable
 columns
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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.
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Example: Using Text Fields
Add a text field to the
preceding example to
let the user set a new
message.
JFrame
ButtonDemo
CheckBoxDemo
TextFieldDemo
RadioButtonDemo
TextFieldDemo
Run
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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.
Appends the string to text in the text area.
+append(s: String): void
+insert(s: String, pos: int): void
Inserts string s in the specified position in the text area.
+replaceRange(s: String, start: int, end: int):
void
Replaces partial text in the range from position start to end with string s.
+getLineCount(): int
Returns the actual number of lines contained in the text area.
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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.
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JTextArea Properties
 text
 editable
 columns
 lineWrap
 wrapStyleWord
 rows
 lineCount
 tabSize
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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
+getToken
DescriptionPanel
+setToken
+paintComponet
-jlblImage: JLabel
+mouseClicked
-jtaTextDescription: JTextArea
-char token
1
1
+getToken
TextAreaDemo
+setToken
+paintComponet
+mouseClicked
+setImageIcon(icon: ImageIcon): void
+setTitle(title: String): void
+setTextDescription(text: String): void
+getMinimumSize(): Dimension
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Example, cont.
TextAreaDemo
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Run
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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.
Removes the item at the specified index in the combo box.
+removeItemAt(anIndex: int): void
+removeAllItems(): void
Removes all items in the combo box.
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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()
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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();
}
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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
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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.
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JList Constructors

JList()
Creates an empty list.

JList(Object[] stringItems)
Creates a new list initialized with items.
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JList Properties
 selectedIndexd
 selectedIndices
 selectedValue
 selectedValues
 selectionMode
 visibleRowCount
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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
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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 blockincrement (decrement) area of the scroll bar, as shown in Figure
13.30.
-unitIncrement: int
Specifies the value added (subtracted) when the user activates the unitincrement (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.
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Scroll Bar Properties
Minimal value
Maximal value
Block decrement
Block increment
Bubble
Unit decrement
Unit increment
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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
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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:
int, value: int)
Creates a slider with the specified orientation, min, max, and value.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
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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
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
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48
Creating Multiple Windows
The following slides show step-by-step how to
create an additional window from an application
or applet.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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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.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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Creating Additional Windows, Step 2
Step 2: Create an instance of SubFrame in the
application or applet.
Example:
SubFrame subFrame = new
SubFrame("SubFrame Title");
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
51
Creating Additional Windows, Step 3
Step 3: Create a JButton for activating the
subFrame.
add(new JButton("Activate SubFrame"));
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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);
}
}
}
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
54
Example, cont.
MultipleWindowsDemo
Run
Histogram
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
55