Podcast
Questions and Answers
What is the relationship between EventObject and AWTEvent in the Java event handling hierarchy?
What is the relationship between EventObject and AWTEvent in the Java event handling hierarchy?
- `AWTEvent` is a generic event class, while `EventObject` is specific to GUI components.
- `EventObject` is a specific type of `AWTEvent`.
- `AWTEvent` is the parent of `EventObject`.
- `EventObject` is the parent of `AWTEvent`. (correct)
Which of the following scenarios would typically result in an ActionEvent?
Which of the following scenarios would typically result in an ActionEvent?
- Clicking a button. (correct)
- Closing a window.
- Entering text in a text field.
- Moving the mouse cursor over a button.
If a class needs to respond to a specific event created by a user's action, what is the most important requirement for that class?
If a class needs to respond to a specific event created by a user's action, what is the most important requirement for that class?
- It must extend the `EventObject` class.
- It must be located in the same package as the event source.
- It must define a `main` method.
- It must implement the appropriate interface and be registered as an event listener. (correct)
Which method is invoked when a mouse button has been pressed and released on a component?
Which method is invoked when a mouse button has been pressed and released on a component?
What is the primary purpose of the getSource() method in the context of event handling?
What is the primary purpose of the getSource() method in the context of event handling?
In the JList class, which selection mode allows users to select multiple, non-adjacent items?
In the JList class, which selection mode allows users to select multiple, non-adjacent items?
Which method is used to determine if any item is selected in a JList?
Which method is used to determine if any item is selected in a JList?
What benefit does using a JScrollPane provide when displaying a component?
What benefit does using a JScrollPane provide when displaying a component?
Which ScrollPaneConstants value would you use to ensure a horizontal scrollbar is always visible, regardless of the content size?
Which ScrollPaneConstants value would you use to ensure a horizontal scrollbar is always visible, regardless of the content size?
In the provided code snippet for LoginForm.java, what is the purpose of the WindowAdapter?
In the provided code snippet for LoginForm.java, what is the purpose of the WindowAdapter?
In the LoginForm.java code, what does the setEchoChar(c:'*') method do for the txtpass field?
In the LoginForm.java code, what does the setEchoChar(c:'*') method do for the txtpass field?
In the ButtonDemo2 class, what is the purpose of implementing the ActionListener interface?
In the ButtonDemo2 class, what is the purpose of implementing the ActionListener interface?
In the UserMan.java code, what is the purpose of the DefaultTableModel?
In the UserMan.java code, what is the purpose of the DefaultTableModel?
What is the purpose of the paintComponent(Graphics g) method override in the Dashboard class's JPanel?
What is the purpose of the paintComponent(Graphics g) method override in the Dashboard class's JPanel?
Which method in the ItemEvent class provides information about the change in an item's state?
Which method in the ItemEvent class provides information about the change in an item's state?
What is the role of the MouseInputListener interface in handling mouse events?
What is the role of the MouseInputListener interface in handling mouse events?
Which method is used to retrieve the Unicode character entered from the keyboard in a KeyEvent?
Which method is used to retrieve the Unicode character entered from the keyboard in a KeyEvent?
What is the purpose of the getClickCount() method in the MouseEvent class?
What is the purpose of the getClickCount() method in the MouseEvent class?
Which method is called when the mouse cursor moves over a component without any mouse buttons being pressed?
Which method is called when the mouse cursor moves over a component without any mouse buttons being pressed?
In the context of event handling, what does it mean to "register" a component as a listener?
In the context of event handling, what does it mean to "register" a component as a listener?
Flashcards
What are Events?
What are Events?
In Java, events represent all activity between the user and the application.
What is EventObject?
What is EventObject?
The parent class for all event objects in Java.
What is an Event Listener?
What is an Event Listener?
An object that contains a method executed when specific events happen.
ActionListener use case
ActionListener use case
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Event Handling Notification
Event Handling Notification
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What is JList class?
What is JList class?
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What is JScrollPane Class?
What is JScrollPane Class?
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What is JList class?
What is JList class?
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getSelectionMode()
getSelectionMode()
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void mouseClicked(MouseEvent e)
void mouseClicked(MouseEvent e)
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int getX()
int getX()
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Study Notes
Lesson 1: Event Handling
- Events in Java are initiated by the user and represent all activity that goes on between the user and the application
- Event objects, like all Java classes, are Objects
- EventObject is the parent class for all event objects and descends from the Object class
- EventObject is the parent of AWTEvent, which is the parent of specific event classes like ActionEvent and ComponentEvent
Common User Actions and Event Types
- ActionEvent results from clicking a button
- MouseEvent results from clicking a component
- ItemEvent results from clicking an item in a list box or a check box
- TextEvent results from changing text in a text field
- WindowEvent results from opening or iconifying a window
- KeyEvent results from pressing a key
Lesson 2: Types of Event
- Event Listener: An object that has a method executed in response to generated events
Listener Types, Events, and Examples
- ActionListener responds to Action events like button clicks
- AdjustmentListener responds to Adjustment events like scroll bar moves
- ChangeListener responds to Change events like when a slider is repositioned
- FocusListener responds to Keyboard focus events like when a text field gains/loses focus
- ItemListener responds to Item events like when a check box changes status
- KeyListener responds to Keyboard events like when text is entered
- MouseListener responds to Mouse events like mouse clicks
- MouseMotionListener responds to Mouse movement events like mouse rolls
- WindowListener responds to Window events like window closes
Events and Event Handling
- Objects can be notified of an event by implementing the appropriate interface and registering as an event listener of the source
- The class of the responding object must have a method that accepts the event object created by the user’s action
- Registering a component (like JFrame) as a listener for another component's events (like JCheckBox) requires writing a method to react to those events
Event Listener Methods
- ActionListener's method is actionPerformed(ActionEvent)
- AdjustmentListener's method is adjustmentValueChanged(AdjustmentEvent)
- FocusListener's methods are focusGained(FocusEvent) and focusLost(FocusEvent)
- ItemListener's method is itemStateChanged(ItemEvent)
AWT Event Class Methods
- EventObject's method, getSource(), returns the Object involved in the event
- ComponentEvent's method, getComponent(), returns the Component involved in the event
- WindowEvent's method, getWindow(), returns the Window involved in the event
- ItemEvent's method, getStateChange(), returns an integer which can be either ItemEvent.SELECTED or ItemEvent.DESELECTED
Useful Event Class Methods
- InputEvent's method, getModifiers(), returns an integer indicating which mouse button was clicked
- MouseEvent's method, getClickCount(), returns the number of mouse clicks
- KeyEvent's method, getKeyChar(), returns the Unicode character entered from the keyboard
Mouse Events
- MouseMotionListener provides mouseDragged() and mouseMoved() to detect mouse rolling or dragging across a component
- MouseListener provides mousePressed(), mouseClicked(), and mouseReleased(), similar to keyboard methods keyPressed(), keyTyped(), and keyReleased()
- MouseInputListener implements all methods from both MouseListener and MouseMotionListener
MouseListener Methods and Descriptions
void mouseClicked(MouseEvent e)is invoked when a mouse button is clicked (pressed and released) on a componentvoid mouseEntered(MouseEvent e)is invoked when the mouse enters a componentvoid mouseExited(MouseEvent e)is invoked when the mouse exits a componentvoid mousePressed(MouseEvent e)is invoked when a mouse button is pressed on a componentvoid mouseReleased(MouseEvent e)is invoked when a mouse button is released on a component
Common MouseMotionListener Methods and Descriptions
void mouseDragged(MouseEvent e)is invoked when the mouse button is pressed on a component and then draggedvoid mouseMoved(MouseEvent e)is invoked when the mouse cursor moves over a component without any buttons being pressed
Methods and Fields of the MouseEvent Class
int getButton()returns which mouse button has changed state, if anyint getClickCount()returns the number of mouse clicks associated with the eventint getX()returns the horizontal x-position of the event relative to the source componentint getY()returns the vertical y-position of the event relative to the source component
Common Fields of the MouseEvent Class
- Mouse button #1 is indicated using
static int BUTTON1and is used bygetButton() - Mouse button #2 is indicated using
static int BUTTON2and is used bygetButton() - Mouse button #3 is indicated using
static int BUTTON3and is used bygetButton() - No mouse buttons is indicated using
static int NOBUTTONand is used bygetButton() - "mouse clicked" event is represented by
static int MOUSE_CLICKED - "mouse dragged" event is represented by
static int MOUSE_DRAGGED - "mouse entered" event is represented by
static int MOUSE_ENTERED - "mouse exited" event is represented by
static int MOUSE_EXITED
Lesson 3: Other Components of Event Handling
- JList displays a list of items like students or files
- Construct a JList object by passing an array of String, similar to JComboBox
JList Selection Modes
- SINGLE_SELECTION allows only one item to be selected
- SINGLE_INTERVAL_SELECTION allows selection of multiple adjacent items
- MULTIPLE_INTERVAL_SELECTION allows selection of multiple non-adjacent items
JList Methods for Selection and Visibility
getFirstVisibleIndex()returns the index of the first visible itemgetLastVisibleIndex()returns the index of the last visible itemgetMinSelectionIndex()returns the smallest selected indexgetMaxSelectionIndex()returns the largest selected indexgetSelectedIndex()returns the first selected item’s index or -1 if there is nonesetSelectedIndex(int index)selects a specific item in the listgetSelectionMode()returns the selection mode (single or multiple)setSelectionMode(int mode)sets whether single or multiple selections are allowedisSelectionEmpty()returns true if no item is selected
JScrollPane Class
- The JScrollPane container holds components needing more display area than allocated
JScrollPane Constructors
- JScrollPane() creates an empty JScrollPane with scroll bars appearing when needed
- JScrollPane(Component) displays the specified component's contents
- JScrollPane(int, int) creates a JScrollPane with both vertical and horizontal scroll bar specifications
- JScrollPane(Component, int, int) displays the specified component and includes both vertical and horizontal scroll bar specifications
Forcing Scrollbar Display
- Use class variables from ScrollPaneConstants
- HORIZONTAL_SCROLLBAR_AS_NEEDED, HORIZONTAL_SCROLLBAR_ALWAYS and HORIZONTAL_SCROLLBAR_NEVER exist
- VERTICAL_SCROLLBAR_AS_NEEDED, VERTICAL_SCROLLBAR_ALWAYS and VERTICAL_SCROLLBAR_NEVER exist
Creating a Scroll Pane Example
- Creates a scroll pane displaying an image named picture with a vertical scrollbar always and no horizontal scrollbar
JScrollPane Methods
createHorizontalScrollBar()returns a JScrollPane.ScrollBar by defaultcreateVerticalScrollBar()returns a JScrollPane.ScrollBar by defaultgetHorizontalScrollBar()returns the horizontal scroll bar that controls the viewport's horizontal view positiongetVerticalScrollBar()returns the vertical scroll bar that controls the viewport's vertical view positionsetHorizontalScrollBar(JScrollBar horizontalScrollBar)adds the scrollbar that controls the viewport's horizontal view position to the scrollpanesetLayout(LayoutManager layout)sets the layout manager for this JScrollPanesetVerticalScrollBar(JScrollBar verticalScrollBar)adds the scrollbar that controls the viewport's vertical view position to the scrollpane
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