Lecture 08Abstract Windows Toolkit

(AWT) and Swing

Jaeki Song

Outline

• GUI Interface• JAVA Graphics API• Event Handling• Layout Managers• JComponents

GUI Interface

• Web-based application use a graphical user interface (GUI)

• The graphical components are bundled in a library known as the Abstract Window Toolkit (AWT)– Mapped to the platform-specific components– Heavyweight components

Why swing?

• The appearance and how theuser interaccts with the program are known as that program’s look and feel.

• javax.swing API makes the look and feel of GUI the same across platforms (lightweight component)

GUI

java.lang.Object

java.awt.Component

java.lang.Container

java.swing.JComponent

The Java Graphics API

AWTEvent

Fon t

FontMetrics

Component

Graphics

Object Color

Container

Panel Applet

Frame

Dialog

Window

JComponent

JApplet

JFrame

JDialog

Swing Components in the javax.swing package

Lightweight

Heavyweight

Classes in the java.awt package

LayoutManager

*

Java Graphics API• Component

– A superclass of all user interface classes• Container

– Used to group components• A layout manager is used to position and place components in a container in

the desired location and style

• JComponent– A super class of all the lightweight

• JFrame– This is a window nor contained inside another window– It is a container that holds another Swing user-interface

components

Java Graphics API

• Jdialog– A popup window or message box generally used as a

temporary window to receive additional information from the user or to provide notification that an event has occurred

• JApplet– A subclass of Applet– You must extend JApplet to create a Swing-based Java Applet

• Jpanel– An invisible container that holds user-interface components– Panel can be nested

Java Graphics API

• Graphics– An abstract class that provides a graphical context for

drawing lines and simple shapes• Color

– A class deals with the colors of graphics components• Font

– Usef for drawings in Grphics• FontMetrics

– An abstract class used to get the properties of the fonts used in drawings

Graphic Classes Classification

• Container classes– JFrame, JPanel, and JApplet

• Component classes– Subclasses of JComponent

• JButton, JTextField, JTextArea, JComboBox, JList, JRadioButton, and JMenu

• Helper classes– Classes used by components and containers to draw and

place objects• Graphics, Color, Font, FontMetrics, Dimension, and Layout

Managers

JComponent.

JButton

JMenuItem

JCheckBoxMenuItem

AbstractButton

JComponent

JMenu

.JRadioButtonMenuItem

.JToggleButton JCheckBox

JRadioButton

.JComboBox

.JInternalFrame .JLayeredPane

.JList .JMenuBar .JOptionPane

.JPopupMenu

.JProgressBar

.JPane

.JFileChooser .JScrollBar .JScrollPane

.JSeparator

.JSplitPane

.JSlider .JTabbedPane

.JTable

.JTableHeader

.JTextField .JTextComponent

.JEditorPane

.JTextArea

.JToolBar

.JToolTip

.JTree

.JRootPane

.JPanel

.JPasswordField

.JColorChooser

.JLabel

Frames

• Frame is a window that is not contained inside another window. Frame is the basis to contain other user interface components in Java graphical applications.

• The Frame class can be used to create windows.

JFrame

• Two constructorspublic JFrame ( )

Creates an untitled JFrame object

public JFrame( String title)Create a JFrame object with a specific title

JFrame Methods

• setVisible (true)– The frame is not visible until setVisible (true)

method is applied• setSize (int, int)

– Specify the frame size• setDefaultCloseOperation (Jframe.EXIT_ON_CLOSE)

– Tells the program to terminate when the frame is closed

Example: Creating JFrame

import javax.swing.*;public class MyFrame{ public static void main(String[] args) { JFrame frame = new JFrame("Test Frame"); frame.setSize(400, 300); frame.setVisible(true); frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE); }

}

Creating Frame

• By default, a frame is displayed in the upper-left corner of the screen. – To display a frame at a specified location, you

can use the setLocation(x, y) method in the JFrame class. This method places the upper-left corner of a frame at location (x, y).

Centering Frames

screenHeight

screenWidth

frameHeight

frameWidth

(x, y)

Frame

Screen

Centering Frames

• Toolkit class– the abstract superclass of all actual implementations of the AWT– getScreenSize( )

• Can be used to obtain screen’s width and height

• Dimension class– Encapsulates the width and height of a component– get.Size method

• Get the size of Dimension object• Return dimension of the object

• JFrame– setLocation (x, y)

Example

• CenterFrame

Event-Driven Programming

• An event can be defined as a type of signal to the program that something has happened. – The event is generated by external user actions such as

mouse movements, mouse button clicks, and keystrokes, or by the operating system, such as a timer

• The GUI component on which an event is generated is called the source object– E.g.

• A button is the source object for a clicking-button action event

Event Classes

Selected User Actions

Source Event TypeUser Action Object GeneratedClicked on a button JButton ActionEvent

Changed text JTextComponent TextEvent

Double-clicked on a list item JList ActionEvent

Selected or deselected an item JList ItemEvent with a single clickSelected or deselected an item JComboBox ItemEvent

Event Handling Model

• GUI event information is stored in an object of a class that extends AWTEvent

• A program performs two key tasks– Event listener

• An object of a class that implements one or more the event-listener interface from package java.awt.event

– Event handler• A method that is automatically called in response to

a particular type of event

Event Handling Model

• Each event-listener interface specifies one or more event handling methods that must be defined in the class that implements the event-listener interface

• The use of event listeners is known as the delegation event model

The Delegation Model

Selected Event Handlers

Event Class Listener Interface Listener Methods (Handlers)ActionEvent ActionListener actionPerformed(ActionEvent)ItemEvent ItemListener itemStateChanged(ItemEvent)WindowEvent WindowListener windowClosing(WindowEvent)

windowOpened(WindowEvent)windowIconified(WindowEvent)windowDeiconified(WindowEvent)windowClosed(WindowEvent)windowActivated(WindowEvent)windowDeactivated(WindowEvent)

• Look at the handout

Inner Class• Classes can be defined inside other classes• Inner classes are used mainly in event handling

• Inner classes with names have the file nameOuterClassName$InnerClassName.class

Public class A extends B {

public class ActionEventHandler implements ActionLister{public void actionPerformed ( ActionEvent e){}

}}

Anonymous Inner Class

• Anonymous inner class (class without a name)• Anonymous inner class have the file name

OuterClassName$#.class– # starts at 1 and is incremented for each anonymous inner class

encountered during compilation

Window.addWindowListner( new WindowAdapter( ) {

public void windowClosing( WindowEvent e){

System.exit(0);}

});

JLabel

• A subclass of Jcomponent• A label is a display area for a short

text, an image, or both. The non-default constructors for labels are as follows:JLabel(String text, int horizontalAlignment)JLabel(String text)JLabel(Icon icon)JLabel(Icon icon, int horizontalAlignment)

Text Components

• Use text component when you want to both display and input information– JTextField

• Allows only a single line of text– JTextArea

• Allows multiple lines of text

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).

• A text field can display information like a label

JTextField Constructors• JTextField(int columns)

– Creates an empty text field with the specified number of columns.• JTextField txtName = new JTextField (20);

• 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.

• JTextField (String, int maximumNumberCharaters)

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.

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.

JTextArea Constructors• JTextArea( )

– Default constructor • Create an empty text area

• 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 Method

• Append method – Allows to add information to the end of the string in a

text area– Use append method to build your output as the

information becomes available to create multiple lines of output

• General FormatcomponentName.append(String);

• ExampletxaInovice.append(“Sold to:” + strName);

Container

• The onscreen display area has a content pane to which the GUI components must be attached so they can be displayed at execution time

• The content pane is an object of class Container from the java.awt package Container c = getContentPane();

Declares Container reference c and assigns it the result of a call to Method getContentPane

Method getContentPane returns a content paneThat can be used to attach GUI components

JPanel

• Panels act as smaller containers for grouping user interface components

JPanel p = new JPanel();• Adding component to a JPanel

– add method• E.g.

– add(ComponentName);

JButton• A button is a component that triggers an action event

when clicked. The following are JButton non-default constructors:JButton(String text)JButton(String text, Icon icon)JButton(Icon icon)

• All button types are subclasses of AbstractButton from javax.swing package– Button types

• Command buttons, check boxes, and radio buttons

• A command button gegnerates an ActionEvent – When the user clicks the button with the mouse

Responding to Jbutton Eventpublic void actionPerformed(ActionEvent e) { // Get the button label JoptionPane.showMessageDialog (null, “You pressed: ”+ e.getActionCommnad() );}

Layout Managers• Java’s layout managers provide a level of abstraction to

automatically map your user interface on all windowing systems.

• The UI components are placed in containers. Each container has a layout manager to arrange the UI components within the container.– FlowLayout– GridLayout– BorderLayout– CardLayout – GridBagLayout

FlowLayout Manager• The components are arranged in the container from left to right in

the order in which they were added. When one row becomes filled, a new row is started.

• FlowLayout Constructors– public FlowLayout(int align, int hGap, int vGap)

• Constructs a new FlowLayout with a specified alignment, horizontal gap, and vertical gap. The gaps are the distances inpixel between components.

– public FlowLayout(int alignment)• Constructs a new FlowLayout with a specified alignment and a default gap of

five pixels for both horizontal and vertical.– public FlowLayout()

• Constructs a new FlowLayout with a default center alignment and a default gap of five pixelsfor both horizontal and vertical.

BorderLayout Manager

• The BorderLayout manager divides the window into five areas: East, South, West, North, and Center.

• Components are added to a BorderLayout– add(Component, constraint), where constraint is

BorderLayout.East, BorderLayout.South, BorderLayout.West", BorderLayout.North", or BorderLayout.Center.

GridLayout Manager

• The GridLayout manager arranges components in a grid (matrix) formation with the number of rows and columns defined by the constructor. The components are placed in the grid from left to right starting with the first row, then the second, and so on.

GridLayout Constructors

• public GridLayout(int rows, int columns)– Constructs a new GridLayout with the specified

number of rows and columns.• public GridLayout(int rows, int columns, int

hGap, int vGap)– Constructs a new GridLayout with the specified

number of rows and columns, along with specified horizontal and vertical gaps between components.

Example

• Tax Systems• Add List• Payroll Systems

JCheckBox

• A check box is a component that enables the user to toggle a choice on or off, like a light switch.– JCheckBox constructors

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

• Example

JRadioButton

• Radio buttons are variations of check boxes. They are often used in the group, where only one button is checked at a time.– JRadioButton constructors

JRadioButton(), JRadioButton(String text)JRadioButton(String text, boolean selected), JRadioButton(Icon

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

• Example: JRadioButton

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. To create a choice, use its default constructor:

JComboBox()

• Example: ComboBoxTest

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.

• JList constructors– JList()

• Creates an empty list.– JList(Object[] stringItems)

• Creates a new list initialized with items.

JSlider

• Enable users to select from a range of integer values

• JSlider inherits from JComponent– tick marks and thumb– The thumb of JSlider to decrease or increase by

1

Menus

• Java provides several classes—JMenuBar, JMenu, JMenuItem, JCheckBoxMenuItem, and JRadioButtonMenuItem —to implement menus in a frame

• A JFrame or JApplet can hold a menu bar to which the pull-down menus are attached. Menus consist of menu items that the user can select (or toggle on or off). Menu bars can be viewed as a structure to support menus.

Menu Demo

The JMenuBar Class

• A menu bar holds menus; the menu bar can only be added to a frame. Following is the code to create and add a JMenuBar to a frame:

JFrame f = new JFrame();f.setSize(300, 200);f.setVisible(true);JMenuBar mb = new JMenuBar(); f.setJMenuBar(mb);

The Menu Class

• You attach menus onto a JMenuBar. The following code creates two menus, File and Help, and adds them to the JMenuBar mb:

JMenu fileMenu = new JMenu("File");JMenu helpMenu = new JMenu("Help");mb.add(fileMenu);mb.add(helpMenu);

The JMenuItem Class

• You add menu items on a menu. The following code adds menu items and item separators inmenu fileMenu:

fileMenu.add(new JMenuItem("new"));fileMenu.add(new JMenuItem("open"));fileMenu.add(new JMenuItem("-"));fileMenu.add(new JMenuItem("print"));fileMenu.add(new JMenuItem("exit"));fileMenu.add(new JMenuItem("-"));

Submenus

• You can add submenus into menu items. The following code adds the submenus “Unix,” “NT,” and “Win95” into the menu item “Software.”JMenu softwareHelpSubMenu = new JMenu("Software");

JMenu hardwareHelpSubMenu = new JMenu("Hardware");

helpMenu.add(softwareHelpSubMenu);

helpMenu.add(hardwareHelpSubMenu);

softwareHelpSubMenu.add(new JMenuItem("Unix"));

softwareHelpSubMenu.add(new JMenuItem("NT"));

softwareHelpSubMenu.add(new JMenuItem("Win95"));

Submenu Demo

JPopupMenus

• A subclass of JComponent– Provide options that are specific to the

component for which the popup trigger event was generated