ICS11 Introduction to Computer Programming II

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Xavier University Computer Center Sun
Microsystems, Philippines
Java sa Eskwela (JsE) Program

• ICS11 Introduction to Computer Programming II
• Joselito dela Cruz Ty

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Chapter 12
Basic Graphical User Interface Components
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Outline

• Swing Overview
• Java GUI Components
• JFrame
• JLabel
• JTextField and JPasswordField
• Jbutton
• JCheckBox and JRadioButton
• JComboBox
• Jlist
• Multiple-Selection Lists
• Event Handling Model
• Mouse Event Handling
• Adapter Classes
• Keyboard Event Handling

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GUI Components

• Graphical User Interface ("Goo-ee")
• pictorial interface to a program
• distinctive "look" and "feel"
• different applications with consistent GUIs
  improve productivity
• GUIs are built from components
• component object with which user interacts
• examples Labels, Text fields, Buttons, Checkboxes

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GUI Components

• Swing GUI components
• defined in package javax.swing
• original GUI components from Abstract Windowing
  Toolkit in java.awt
• heavyweight components rely on local platform's
  windowing system for look and feel

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GUI Components

• Swing GUI components
• Swing components are lightweight
• written in Java, not weighed down by complex GUI
  capabilities of platform
• more portable than heavyweight components
• Swing components allow programmer to specify look
  and feel
• can change depending on platform
• can be the same across all platforms

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GUI Components

• Swing component inheritance hierarchy

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GUI Components

• Swing component inheritance hierarchy
• Component defines methods that can be used in its
  subclasses (for example, paint and repaint)
• Container collection of related components
• when using JFrames, attach components to the
  content pane (a Container)
• method add
• JComponent - superclass to most Swing components
• much of a component's functionality inherited
  from these classes

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GUI Demo
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JApplet Methods

• public void init()
• called when applet is loaded for execution
• public void start()
• called after init() and everytime the user
  returns to HTMl page
• public void paint(Graphics g)
• called after start() and after every call to
  update() or repaint()
• public void stop()
• called when user leaves the webpage
• public void destroy()
• called when applet is being removed from memory

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Class JFrame

• Is usually extended to make a JFrame object
• Constructors
• JFrame() initially invisible
• JFrame(String title) sets the title
• Method
• setTitle( String title )
• sets title bar of window

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JLabel

• provide text instructions on a GUI
• read-only text
• programs rarely change a label's contents
• A JLabel does not react to any users actions

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JLabel

• Constructors
• JLabel()
• JLabel(Icon image)
• JLabel(Icon image,int hAlignment)
• JLabel(String text)
• JLabel(String txt,Icon i,int hAlignment)
• JLabel(String text, int hAlignment)
• Text_Alignment_CONSTANT can be
• SwingConstants.LEFT
• SwingConstants.RIGHT
• SwingConstants.BOTTOM
• SwingConstants.CENTER

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JLabel

• Methods
• setToolTipText(String s)
• displays s in a tool tip when mouse over label
• setText(String text)
• getText()
• setIcon(Icon i)
• setHorizontalTextPosition(int t)
• setHorizontalAlignment(int t)

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JLabel

• Icon
• Object that implements interface Icon
• one class is ImageIcon (.gif and .jpeg images)
• Icon myIconnew ImageIcon("bug1.gif")
• myLabel.setIcon( myIcon )
• myLabel.getIcon

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JTextField

• single line areas in which text can be entered or
  displayed
• JPasswordFields show inputted text as an asterisk
  
• JPasswordField extends JTextField

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JTextField

• Constructors
• JTextField()
• JTextField(int columns)
• JTextField(String text)
• JTextField(String text,int columns)
• Methods
• setText()
• getText()
• setEditable(boolean editable )
• getPassword()

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JTextArea

• Constructors
• JTextArea()
• JTextField(int rows, int columns)
• JTextField(String text)
• JTextField(String text, int rows, int columns)
• Methods
• append()
• getLineCount()
• insert(String text, int position)
• setColumns(int columns)
• setRows()
• setText()
• getText()
• setEditable(boolean editable )

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Buttons

• Button
• a component the user clicks to trigger an action
• several types of buttons
• command buttons
• toggle buttons
• check boxes
• radio buttons

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JButton

• Command button
• generates ActionEvent when clicked
• created with class JButton
• JButton
• text on face called button label
• each button should have a different label
• support display of Icons

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JButton

• Constructors
• JButton()
• JButton(Icon a)
• JButton(String text)
• JButton(String text, Icon a)
• Methods of class JButton
• setRolloverIcon( myIcon )

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JToggleButton

• Abstract superclass of state buttons
• subclasses JCheckBox, JRadioButton
• have on/off (true/false) values

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JCheckBox

• Constructors
• JCheckBox()
• JCheckBox(Icon a)
• JCheckBox(Icon a, boolean selected)
• JCheckBox(String a)
• JCheckBox(String a, boolean selected)
• JCheckBox(String a, Icon a)
• JCheckBox(String a, Icon a, boolean selected)

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JCheckBox

• Methods
• JCheckBox()
• JCheckBox(Icon a)
• JCheckBox(Icon a, boolean selected)
• JCheckBox(String a)
• JCheckBox(String a, boolean selected)
• JCheckBox(String a, Icon a)
• JCheckBox(String a, Icon a, boolean selected)

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JRadioButton

• Radio buttons
• have two states selected and deselected
• normally appear as a group
• only one radio button in the group can be
  selected at time
• selecting one button turns off the other buttons
  in the same group
• ButtonGroup - maintains logical relationship
  between radio buttons

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JRadioButton

• Constructors
• JRadioButton()
• JRadioButton(Icon a)
• JRadioButton(Icon a, boolean selected)
• JRadioButton(String text)
• JRadioButton(String text,boolean slected)
• JRadioButton(String text, Icon a)
• JRadioButton(String text, Icon a, boolean
  selected)

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JRadioButton

• Class ButtonGroup
• ButtonGroup myGroup new ButtonGroup()
• binds radio buttons into logical relationship
• method add
• associate a radio button with a group
• myGroup.add( myRadioButton )

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JComboBox

• Drop down list
• List of items, user makes a selection

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JComboBox

• Constructors
• JComboBox()
• JComboBox(Object list)
• Methods
• numeric index keeps track of elements
• first element added at index 0
• first item added appears as currently selected
  item when combo box appears
• addItem(Object add)
• insertItemAt(Object a,int index)

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JComboBox

• Methods
• getItemAt(int index)
• getItemCount()
• getSelectedIndex()
• getSelectedItem()
• getSelectedObjects()
• removeAllItems()
• removeItem(Object a)
• removeItemAt(int index)
• setEditable(boolean tf)
• setMaximumRowCount(int count)

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JList

• List
• displays series of items, may select one or more
• this section, discuss single-selection lists

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JList

• Constructors
• JList()
• JList(Object listitems)
• Methods
• getSelectedIndex()
• getSelectedIndeces()
• getSelectedValue()
• getSelectedValues()
• getElementAt(int index)
• setSelectedIndex()
• setSelectedValue()
• setListData()
• setVisibleRowCount(int rows)

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JScrollPane

• JScrollPane object used for scrolling
• takes component to which to add scrolling as
  argument
• add JScrollPane object to content pane
• example
• JList colorListnew JList()4
• c.add( new JScrollPane(colorList))

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JList

• Methods
• setSelectionMode(selection_CONST)
• SINGLE_SELECTION
• one item selected at a time
• SINGLE_INTERVAL_SELECTION
• select a contiguous group of items by holding
  Shift key
• MULTIPLE_INTERVAL_SELECTION
• select any amount of items
• hold Ctrl key and click each item to select

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Layout Managers

• Layout managers
• arrange GUI components on a container
• provide basic layout capabilities
• easier to use than determining exact size and
  position of every component
• programmer concentrates on "look and feel" rather
  than details

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FlowLayout

• c.setLayout(new FlowLayout())
• Most basic layout manager
• components placed left to right in order added
• when edge of container reached, continues on next
  line
• components can be left-aligned, centered
  (default), or right-aligned
• setAlignment( position_CONSTANT )
• FlowLayout.LEFT, FlowLayout.CENTER,
  FlowLayout.RIGHT

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Layout Managers
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BorderLayout

• c.setLayout(new BorderLayout())
• default manager for content pane
• arrange components into 5 regions
• North, south, east, west, center
• up to 5 components can be added directly
• One for each region

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BorderLayout

• adding components with BorderLayout layout
  manager
• c.add(component,position)
• position BorderLayout.NORTH
• SOUTH, EAST, WEST, CENTER similar

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BorderLayout
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GridLayout

• c.setLayout(new GridLayout())
• divides container into a grid
• components placed in rows and columns
• all components have same width and height
• added starting from top left, then from left to
  right
• when row full, continues on next row, left to
  right

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GridLayout

• Constructors
• GridLayout( rows, columns, hGap, vGap )
• specify number of rows and columns, and
  horizontal and vertical gaps between elements (in
  pixels)
• GridLayout( rows, columns )
• default 0 for hGap and vGap

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Layout Managers

• Complex GUIs
• each component needs to be placed in an exact
  location
• can use multiple panels
• each panel's components arranged in a specific
  layout

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Panels

• Panels
• class JPanel inherits from JComponent, which
  inherits from java.awt.Container
• every JPanel is a Container
• JPanels can have components (and other JPanels)
  added to them
• JPanel sized to components it contains
• grows to accommodate components as they are added

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Panels

• Panel Usage
• create panels, and set the layout for each
• add components to the panels as needed
• add the panels to the content pane (default
  BorderLayout)

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Null Layout Manager

• c.setLayout(null)
• No layout manager will be used
• Position of components will be determined by the
  method
• component.setBounds(x,y,width,height)

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GUI Events

• GUIs are event driven
• generate events when user interacts with GUI
• mouse movements, mouse clicks, typing in a text
  field, etc.
• event information stored in object that extends
  AWTEvent

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GUI Events

• To process an event
• register an event listener
• Object from a class that implements an
  event-listener interface (from java.awt.event or
  javax.swing.event)
• e.g. buttonA.addActionListener(this)
• "Listens" for events
• implement event handler
• method that is called in response to an event
• event handling interface has one or more methods
  that must be defined

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GUI Events

• When an event occurs
• GUI component notifies its listeners
• calls listener's event handling method
• Delegation event model
• use of event listeners in event handling
• processing of event delegated to particular
  object
• See eTest2.java

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GUI Events

• Registering event listeners
• all JComponents contain an object of class
  EventListenerList called listenerList
• when text1.addActionListener(handler) executes
• new entry placed into listenerList

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GUI Events

• Handling events
• when event occurs, has an event ID
• component uses this to decide which method to
  call
• if ActionEvent, then actionPerformed called (in
  all registered ActionListeners)

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GUI Component Events

• JLabel
• does not respond to any event

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GUI Component Events

• JTextField, JPasswordField,JButton, JCheckBox,
  JRadioButton
• ActionListener(ActionEvent e)
• getActionCommand
• returns text in JTextField that generated event
  or the labels in JButton, JCheckBox, and
  JRadioButton that generated the event
• getSource
• getSource returns a Component reference to
  component that generated event

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GUI Component Events

• JCheckBox, JRadioButton, JComboBox
• ItemEvent generated every time buttons change or
  item is selected
• handled by an ItemListener, which must define
  itemStateChanged
• register handlers with addItemListener
• private class CheckBoxHandler implements
  ItemListener
• public void itemStateChanged( ItemEvent e )

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GUI Component Events

• JCheckBox, JRadioButton, JComboBox
• Class ItemEvent.getStateChange
• returns ItemEvent.SELECTED or ItemEvent.DESELECTED

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GUI Component Events

• JList
• ListSelectionListener
• valueChanged(ListSelectionEvent e)
• register handler with addListSelectionListener

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Mouse Events

• Mouse events
• can be trapped for any GUI component derived from
  java.awt.Component
• mouse event handling methods
• take a MouseEvent object
• contains info about event, including x and y
  coordinates
• methods getX and getY
• MouseListener and MouseMotionListener
• addMouseListener
• addMouseMotionListener

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Mouse Events

• Interface MouseListener
• public void mousePressed( MouseEvent e )
• Mouse pressed on a component
• public void mouseClicked( MouseEvent e )
• Mouse pressed and released
• public void mouseReleased( MouseEvent e )
• Mouse released
• public void mouseEntered( MouseEvent e )
• Mouse enters bounds of component
• public void mouseExited( MouseEvent e )
• Mouse leaves bounds of component

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Mouse Events

• Interface MouseMotionListener
• public void mouseDragged( MouseEvent e )
• Mouse pressed and moved
• public void mouseMoved( MouseEvent e )
• Mouse moved when over component

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Adapter Classes

• time consuming to define all interface methods
• MouseListener and MouseMotionListener have seven
  methods
• What if we only want to use one?
• Required to define all methods in interface

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Adapter Classes

• implements an interface
• default implementation (empty body) for all
  methods
• programmer extends adapter class
• overrides methods he wants to use
• has "is a" relationship with interface
• MouseAdapter is a MouseListener

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Adapter Classes

• ComponentAdapter ComponentListener
• ContainerAdapter ContainerListener
• FocusAdapter FocusListener
• KeyAdapter KeyListener
• MouseAdapter MouseListener
• MouseMotionAdapter MouseMotionListener
• WindowAdapter WindowListener

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Mouse Events

• Class MouseEvent
• inherits from InputEvent
• can distinguish between buttons on multi-button
  mouse
• combination of a mouse click and a keystroke
• Java assumes every mouse has a left mouse button
• Alt click center mouse button
• Meta click right mouse button

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Mouse Events

• Class MouseEvent
• method getClickCount
• returns number of mouse clicks (separate for each
  button)
• methods isAltDown and isMetaDown
• returns true if Alt or Meta key down when mouse
  clicked

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Keyboard Events

• Interface KeyListener
• handles key events (keys pressed on keyboard)
• must define methods
• keyPressed - called when any key pressed
• keyTyped - called when non-action key pressed
• action keys arrow keys, home, end, page up, page
  down, function keys, num lock, print screen,
  scroll lock, caps lock, pause

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Keyboard Events

• Interface KeyListener
• must define methods (continued)
• keyReleased - called for any key after it is
  released
• each get a KeyEvent as an argument
• subclass of InputEvent

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Keyboard Events

• KeyEvent methods
• getKeyCode
• every key represented with a virtual key code
  (constant)
• complete list in on-line documentation
  (java.awt.event)
• getKeyText
• takes key code constant, returns name of key

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Keyboard Events

• KeyEvent methods
• getKeyChar
• gets Unicode character of key pressed
• isActionKey
• returns true if key that generated event is an
  action key

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Keyboard Events

• KeyEvent methods
• getModifiers (from class InputEvent)
• returns which modifiers were pressed
• getKeyModifierText ( e.getModifiers )
• returns string containing names of modifier keys