16 Slide Creating User Interface

1Liang, Introduction to Java Programming, Seventh Edition, (c) 2009 Pearson Education, Inc. All rights reserved. 0136012671

Chapter 16Creating User Interfaces


MotivationsA 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 (see Figure 16.1).


Objectives To create graphical user interfaces with various user-

interface components: JButton, JCheckBox, JRadioButton, JLabel, JTextField, JTextArea, JComboBox, JList, JScrollBar, and JSlider (§§16.2–16.11).

To create listeners for various types of events (§§16.2–16.11).

To display multiple windows in an application (§16.12).


Components Covered in the ChapterIntroduces the frequently used GUI componentsUses borders and icons

AbstractButton

JToggleButton

JCheckBox

JRadioButton

JComboBox

JList

JSlider

JTextComponent

JLabel

JButton

Component Container JComponent

JTextField

JTextArea

JScrollBar

JPasswordField


ButtonsA 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.


javax.swing.AbstractButton

-actionCommand: String

-text: String

-icon: javax.swing.Icon

-pressedIcon: javax.swing.Icon

-rolloverIcon: javax.swing.Icon

-mnemonic: int

-horizontalAlignment: int

-horizontalTextPosition: int

-verticalAlignment: int

-verticalTextPosition: int

-borderPainted: boolean

-iconTextGap: int

-selected(): boolean

The action command of this button.

The button’s text (i.e., the text label on the button).

The button’s default icon. This icon is also used as the "pressed" and "disabled" icon if there is no explicitly set pressed icon.

The pressed icon (displayed when the button is pressed).

The rollover icon (displayed when the mouse is over the button).

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.

The horizontal alignment of the icon and text (default: CENTER).

The horizontal text position relative to the icon (default: RIGHT).

The vertical alignment of the icon and text (default: CENTER).

The vertical text position relative to the icon (default: CENTER).

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.

The gap between the text and the icon on the button (JDK 1.4).

The state of the button. True if the check box or radio button is selected, false if it's not.

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.

AbstractButton


JButtonJButton inherits AbstractButton and provides several constructors to create buttons.

javax.swing.JButton

+JButton()

+JButton(icon: javax.swing.Icon)

+JButton(text: String)

+JButton(text: String, icon: Icon)

Creates a default button with no text and icon.

Creates a button with an icon.

Creates a button with text.

Creates a button with text and an icon.



JButton Constructors

The following are JButton constructors:

JButton()

JButton(String text)

JButton(String text, Icon icon)

JButton(Icon icon)


JButton Properties text icon mnemonic horizontalAlignment verticalAlignment horizontalTextPosition verticalTextPosition iconTextGap


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


Demo

RunRun

TestButtonIconsTestButtonIcons


Horizontal AlignmentsHorizontal 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.


Vertical AlignmentsVertical 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.


Horizontal Text PositionsHorizontal 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.


Vertical Text PositionsVertical 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.


Example: Using ButtonsWrite 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.

RunRun

ButtonDemoButtonDemo

JButton JButton

MessagePanel


JCheckBoxJCheckBox 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.JCheckBox

+JCheckBox()

+JCheckBox(text: String)

+JCheckBox(text: String, selected: boolean)

+JCheckBox(icon: Icon)

+JCheckBox(text: String, icon: Icon)

+JCheckBox(text: String, icon: Icon, selected: boolean)

Creates a default check box button with no text and icon.

Creates a check box with text.

Creates a check box with text and specifies whether the check box is initially selected.

Creates a checkbox with an icon.

Creates a checkbox with text and an icon.

Creates a check box with text and an icon, and specifies whether the check box is initially selected.


javax.swing.JToggleButton


Example: Using Check BoxesAdd three check boxes named Centered, Bold, and Italic into Example 16.1 to let the user specify whether the message is centered, bold, or italic.

CheckBoxDemoCheckBoxDemo RunRun

ButtonDemo

CheckBoxDemo


JRadioButtonRadio buttons are variations of check boxes. They are often used in the group, where only one button is checked at a time.

javax.swing.JRadioButton

+JRadioButton()

+JRadioButton(text: String)

+JRadioButton(text: String, selected: boolean)

+JRadioButton(icon: Icon)

+JRadioButton(text: String, icon: Icon)

+JRadioButton(text: String, icon: Icon, selected: boolean)

Creates a default radio button with no text and icon.

Creates a radio button with text.

Creates a radio button with text and specifies whether the radio button is initially selected.

Creates a radio button with an icon.

Creates a radio button with text and an icon.

Creates a radio button with text and an icon, and specifies whether the radio button is initially selected.


javax.swing.JToggleButton


Grouping Radio Buttons

ButtonGroup btg = new ButtonGroup();

btg.add(jrb1);

btg.add(jrb2);


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

RunRunRadioButtonDemoRadioButtonDemo

ButtonDemo

CheckBoxDemo

RadioButtonDemo


JLabelA label is a display area for a short text, an image, or both.

javax.swing.JLabel -text: String

-icon: javax.swing.Icon


-horizontalTextPosition: int

-verticalAlignment: int

-verticalTextPosition: int

-iconTextGap: int

+JLabel()

+JLabel(icon: javax.swing.Icon)

+JLabel(icon: Icon, hAlignment: int)

+JLabel(text: String)

+JLabel(text: String, icon: Icon, hAlignment: int)

+JLabel(text: String, hAlignment: int)

The label’s text.

The label’s image icon.

The horizontal alignment of the text and icon on the label.

The horizontal text position relative to the icon on the label.

The vertical alignment of the text and icon on the label.

The vertical text position relative to the icon on the label.

The gap between the text and the icon on the label (JDK 1.4).

Creates a default label with no text and icon.

Creates a label with an icon.

Creates a label with an icon and the specified horizontal alignment.

Creates a label with text.

Creates a label with text, an icon, and the specified horizontal alignment.

Creates a label with text and the specified horizontal alignment.




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)


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.


Using Labels// Create an image icon from image fileImageIcon icon = new ImageIcon("image/grapes.gif"); // Create a label with text, an icon, // with centered horizontal alignmentJLabel jlbl = new JLabel("Grapes", icon, SwingConstants.CENTER); // Set label's text alignment and gap between text and iconjlbl.setHorizontalTextPosition(SwingConstants.CENTER);jlbl.setVerticalTextPosition(SwingConstants.BOTTOM);jlbl.setIconTextGap(5);


JTextFieldA 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.JTextField -columns: int


+JTextField()

+JTextField(column: int)

+JTextField(text: String)

+JTextField(text: String, columns: int)

The number of columns in this text field.

The horizontal alignment of this text field (default: LEFT).

Creates a default empty text field with number of columns set to 0.

Creates an empty text field with specified number of columns.

Creates a text field initialized with the specified text.

Creates a text field initialized with the specified text and columns.

javax.swing.text.JTextComponent -text: String

-editable: boolean

The text contained in this text component.

Indicates whether this text component is editable (default: true).



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 thespecified text and the column size.


JTextField PropertiestexthorizontalAlignmenteditablecolumns


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.


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

RunRunTextFieldDemoTextFieldDemo

JFrame ButtonDemo CheckBoxDemo RadioButtonDemo TextFieldDemo


JTextAreaIf 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.JTextArea -columns: int

-rows: int

-tabSize: int

-lineWrap: boolean

-wrapStyleWord: boolean

+JTextArea()

+JTextArea(rows: int, columns: int)

+JTextArea(text: String)

+JTextArea(text: String, rows: int, columns: int)

+append(s: String): void

+insert(s: String, pos: int): void

+replaceRange(s: String, start: int, end: int): void

+getLineCount(): int

The number of columns in this text area.

The number of rows in this text area.

The number of characters used to expand tabs (default: 8).

Indicates whether the line in the text area is automatically wrapped (default: false).

Indicates whether the line is wrapped on words or characters (default: false).

Creates a default empty text area.

Creates an empty text area with the specified number of rows and columns.

Creates a new text area with the specified text displayed.

Creates a new text area with the specified text and number of rows and columns.

Appends the string to text in the text area.

Inserts string s in the specified position in the text area.

Replaces partial text in the range from position start to end with string s.

Returns the actual number of lines contained in the text area.

javax.swing.text.JTextComponent



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 andthe number of rows and columns specified.


JTextArea PropertiestexteditablecolumnslineWrapwrapStyleWordrowslineCounttabSize


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.

DescriptionPanel -jlblImage: JLabel -jtaTextDescription: JTextArea +setImageIcon(icon: ImageIcon): void +setTitle(title: String): void +setTextDescription(text: String): void +getMinimumSize(): Dimension

1 TextAreaDemo

JPanel -char token +getToken +setToken +paintComponet +mouseClicked

JFrame -char token +getToken +setToken +paintComponet +mouseClicked

1


Example, cont.

RunRunTextAreaDemoTextAreaDemo


JComboBoxA 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.JComboBox

+JComboBox()

+JComboBox(items: Object[])

+addItem(item: Object): void

+getItemAt(index: int): Object

+getItemCount(): int

+getSelectedIndex(): int

+setSelectedIndex(index: int): void

+getSelectedItem(): Object

+setSelectedItem(item: Object): void

+removeItem(anObject: Object): void

+removeItemAt(anIndex: int): void

+removeAllItems(): void

Creates a default empty combo box.

Creates a combo box that contains the elements in the specified array.

Adds an item to the combo box.

Returns the item at the specified index.

Returns the number of items in the combo box.

Returns the index of the selected item.

Sets the selected index in the combo box.

Returns the selected item.

Sets the selected item in the combo box.

Removes an item from the item list.

Removes the item at the specified index in the combo box.

Removes all items in the combo box.



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()


Using theitemStateChanged Handler

public void itemStateChanged(ItemEvent e) { // Make sure the source is a combo box if (e.getSource() instanceof JComboBox) String s = (String)e.getItem();}

When a choice is checked or unchecked, itemStateChanged() for ItemEvent is invoked as well as the actionPerformed() handler for ActionEvent.


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.

RunRunComboBoxDemoComboBoxDemo


JListA 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.JList

+JList()

+JList(items: Object[])

+getSelectedIndex(): int

+setSelectedIndex(index: int): void

+getSelectedIndices(): int[]

+setSelectedIndices(indices: int[]): void

+getSelectedValue(): Object

+getSelectedValues(): Object[]

+getVisibleRowCount(): int

+setVisibleRowCount(count: int): void

+getSelectionBackground(): Color

+setSelectionBackground(c: Color): void

+getSelectionForeground(): Color

+setSelectionForeground(c: Color): void

+getSelectionMode(): int

+setSelectionMode(selectionMode: int):

Creates a default empty list.

Creates a list that contains the elements in the specified array.

Returns the index of the first selected item.

Selects the cell at the specified index.

Returns an array of all of the selected indices in increasing order.

Selects the cells at the specified indices.

Returns the first selected item in the list.

Returns an array of the values for the selected cells in increasing index order.

Returns the number of visible rows displayed without a scrollbar. (default: 8)

Sets the preferred number of visible rows displayed without a scrollbar.

Returns the background color of the selected cells.

Sets the background color of the selected cells.

Returns the foreground color of the selected cells.

Sets the foreground color of the selected cells.

Returns the selection mode for the list.

Sets the selection mode for the list.



JList Constructors JList()

Creates an empty list.

JList(Object[] stringItems)

Creates a new list initialized with items.


JList Properties

selectedIndexd

selectedIndices

selectedValue

selectedValues

selectionMode

visibleRowCount


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.

RunRunListDemoListDemo


JScrollBarA 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.JScrollBar -orientation: int

-maximum: int

-minimum: int

-visibleAmount: int

-value: int

-blockIncrement: int

-unitIncrement: int

+JScrollBar()

+JScrollBar(orientation: int)

+JScrollBar(orientation: int, value: int, extent: int, min: int, max: int)

Specifies horizontal or vertical style, default is horizontal.

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.

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.

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.

Represents the current value of the scroll bar.

Specifies value added (subtracted) when the user activates the block-increment (decrement) area of the scroll bar, as shown in Figure 13.30.

Specifies the value added (subtracted) when the user activates the unit-increment (decrement) area of the scroll bar, as shown in Figure 13.30.

Creates a default vertical scroll bar.

Creates a scroll bar with the specified orientation.

Creates a scrollbar with the specified orientation, value, extent, minimum, and maximum.




Scroll Bar Properties

Bubble

Unit increment

Block decrement Block increment

Minimal value Maximal value

Unit decrement


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.

ScrollBarDemoScrollBarDemo RunRun


JSliderJSlider is similar to JScrollBar, but JSlider has more properties and can appear in many forms.

javax.swing.JSlider -maximum: int

-minimum: int

-value: int

-orientation: int

-paintLabels: boolean

-paintTicks: boolean

-paintTrack: boolean

-majorTickSpacing: int

-minorTickSpacing: int

-inverted: boolean

+JSlider()

+JSlider(min: int, max: int)

+JSlider(min: int, max: int, value: int)

+JSlider(orientation: int)

+JSlider(orientation: int, min: int, max: int, value: int)

The maximum value represented by the slider (default: 100).

The minimum value represented by the slider (default: 0).

The current value represented by the slider.

The orientation of the slider (default: JSlider.HORIZONTAL).

True if the labels are painted at tick marks (default: false).

True if the ticks are painted on the slider (default: false).

True if the track is painted on the slider (default: true).

The number of units between major ticks (default: 0).

The number of units between minor ticks (default: 0).

True to reverse the value-range, and false to put the value range in the normal order (default: false).

Creates a default horizontal slider.

Creates a horizontal slider using the specified min and max.

Creates a horizontal slider using the specified min, max, and value.

Creates a slider with the specified orientation.

Creates a slider with the specified orientation, min, max, and value.




Example: Using Sliders

Rewrite the preceding program using the sliders to control a message displayed on a panel instead of using scroll bars.

SliderDemoSliderDemo RunRun


Creating Multiple Windows

The following slides show step-by-step how to create an additional window from an application or applet.


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

Creating Additional Windows, Step 1



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

Example:

SubFrame subFrame = new

SubFrame("SubFrame Title");



Step 3: Create a JButton for activating the subFrame.

add(new JButton("Activate SubFrame"));



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); } }}


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.


Example, cont.

RunRunMultipleWindowsDemoMultipleWindowsDemo

HistogramHistogram

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16 Slide Creating User Interface