15 Slide

Chapter 15 Creating User Interfaces

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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 (§15.2 – 15.12). To create listeners for various types of events (§15.2 – 15.12). To use borders to visually group user-interface components (§15.2). To create image icons using the ImageIcon class (§15.3). To display multiple windows in an application (§15.14).

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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 javax.swing.AbstractButton

The get and set methods for these data fields are provided in the class, but omitted in the UML diagram for brevity.

-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). 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.

-mnemonic: int

-horizontalTextPosition: int

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

-horizontalAlignment: int

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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 Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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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

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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

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 Example 15.1 to let the user specify whether the message is centered, bold, or italic. ButtonDemo

CheckBoxDemo

CheckBoxDemo

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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

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JLabel A label is a display area for a short text, an image, or both. javax.swing.JComponent javax.swing.JLabel

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 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); Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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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 -horizontalAlignment: int

The number of columns in this text field. 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. Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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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

RadioButtonDemo

TextFieldDemo

TextFieldDemo Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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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 Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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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 Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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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(); } Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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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 Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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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. Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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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 Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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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 Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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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. Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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Scroll Bar Properties Minimal value

M aximal 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 Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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

The get and set methods for these data fields are provided in the class, but omitted in the UML diagram for brevity.

-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.

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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

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

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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.

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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");

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

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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); } } }

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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.

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Example, cont.

MultipleWindowsDemo Histogram Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

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