Java Event Handling

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Questions and Answers

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`?

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?

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?

<code>mouseClicked(MouseEvent e)</code> (A)

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What is the primary purpose of the `getSource()` method in the context of event handling?

To identify the object that triggered the event. (C)

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In the `JList` class, which selection mode allows users to select multiple, non-adjacent items?

<code>MULTIPLE_INTERVAL_SELECTION</code> (A)

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Which method is used to determine if any item is selected in a `JList`?

<code>isSelectionEmpty()</code> (B)

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What benefit does using a `JScrollPane` provide when displaying a component?

It provides scrollbars when the component's content exceeds the available display area. (D)

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Which `ScrollPaneConstants` value would you use to ensure a horizontal scrollbar is always visible, regardless of the content size?

<code>HORIZONTAL_SCROLLBAR_ALWAYS</code> (A)

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In the provided code snippet for `LoginForm.java`, what is the purpose of the `WindowAdapter`?

To customize the window closing behavior and prompt for confirmation. (B)

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In the `LoginForm.java` code, what does the `setEchoChar(c:'*')` method do for the `txtpass` field?

It sets the character to be used for echoing password input, masking the actual text. (C)

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In the `ButtonDemo2` class, what is the purpose of implementing the `ActionListener` interface?

To respond to the button click event and change the button's text. (D)

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In the `UserMan.java` code, what is the purpose of the `DefaultTableModel`?

To manage the data displayed in the <code>JTable</code>. (C)

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What is the purpose of the `paintComponent(Graphics g)` method override in the `Dashboard` class's `JPanel`?

To paint a background image on the panel. (B)

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Which method in the `ItemEvent` class provides information about the change in an item's state?

<code>getStateChange()</code> (C)

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What is the role of the MouseInputListener interface in handling mouse events?

It combines the functionalities of both MouseListener and MouseMotionListener interfaces. (D)

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Which method is used to retrieve the Unicode character entered from the keyboard in a `KeyEvent`?

<code>getKeyChar()</code> (B)

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What is the purpose of the `getClickCount()` method in the `MouseEvent` class?

To get the number of times the mouse was clicked. (C)

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Which method is called when the mouse cursor moves over a component without any mouse buttons being pressed?

<code>mouseMoved(MouseEvent e)</code> (C)

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In the context of event handling, what does it mean to "register" a component as a listener?

To associate the component with an event source so it can receive notifications. (C)

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Flashcards

What are Events?

In Java, events represent all activity between the user and the application.

What is EventObject?

The parent class for all event objects in Java.

What is an Event Listener?

An object that contains a method executed when specific events happen.

ActionListener use case

ActionListener responds to Action events like button clicks.

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Event Handling Notification

Any object can be notified of an event if it implements the interface and is registered.

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What is JList class?

Requires a display of a list of items.

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What is JScrollPane Class?

Hold components that require more display area.

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What is JList class?

Used to display a list of items, such as a list of students, a list of files, and so forth.

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getSelectionMode()

Returns the selection mode (single or multiple).

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void mouseClicked(MouseEvent e)

Invoked when a mouse button has been clicked (pressed and released) on a component

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int getX()

Returns the horizontal x-position of the event relative to the source component

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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 component
void mouseEntered(MouseEvent e) is invoked when the mouse enters a component
void mouseExited(MouseEvent e) is invoked when the mouse exits a component
void mousePressed(MouseEvent e) is invoked when a mouse button is pressed on a component
void 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 dragged
void 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 any
int getClickCount() returns the number of mouse clicks associated with the event
int getX() returns the horizontal x-position of the event relative to the source component
int 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 BUTTON1 and is used by getButton()
Mouse button #2 is indicated using static int BUTTON2 and is used by getButton()
Mouse button #3 is indicated using static int BUTTON3 and is used by getButton()
No mouse buttons is indicated using static int NOBUTTON and is used by getButton()
"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 item
getLastVisibleIndex() returns the index of the last visible item
getMinSelectionIndex() returns the smallest selected index
getMaxSelectionIndex() returns the largest selected index
getSelectedIndex() returns the first selected item’s index or -1 if there is none
setSelectedIndex(int index) selects a specific item in the list
getSelectionMode() returns the selection mode (single or multiple)
setSelectionMode(int mode) sets whether single or multiple selections are allowed
isSelectionEmpty() 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 default
createVerticalScrollBar() returns a JScrollPane.ScrollBar by default
getHorizontalScrollBar() returns the horizontal scroll bar that controls the viewport's horizontal view position
getVerticalScrollBar() returns the vertical scroll bar that controls the viewport's vertical view position
setHorizontalScrollBar(JScrollBar horizontalScrollBar) adds the scrollbar that controls the viewport's horizontal view position to the scrollpane
setLayout(LayoutManager layout) sets the layout manager for this JScrollPane
setVerticalScrollBar(JScrollBar verticalScrollBar) adds the scrollbar that controls the viewport's vertical view position to the scrollpane

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Java Event Handling

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Podcast

Questions and Answers

What is the relationship between EventObject and AWTEvent in the Java event handling hierarchy?

Which of the following scenarios would typically result in an ActionEvent?

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?

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?

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?

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?

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 ButtonDemo2 class, what is the purpose of implementing the ActionListener interface?

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?

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?

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?

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?

Flashcards

What are Events?

What is EventObject?

What is an Event Listener?

ActionListener use case

Event Handling Notification

What is JList class?

What is JScrollPane Class?

What is JList class?

getSelectionMode()

void mouseClicked(MouseEvent e)

int getX()

Study Notes

Lesson 1: Event Handling

Common User Actions and Event Types

Lesson 2: Types of Event

Listener Types, Events, and Examples

Events and Event Handling

Event Listener Methods

AWT Event Class Methods

Useful Event Class Methods

Mouse Events

MouseListener Methods and Descriptions

Common MouseMotionListener Methods and Descriptions

Methods and Fields of the MouseEvent Class

Common Fields of the MouseEvent Class

Lesson 3: Other Components of Event Handling

JList Selection Modes

JList Methods for Selection and Visibility

JScrollPane Class

JScrollPane Constructors

Forcing Scrollbar Display

Creating a Scroll Pane Example

JScrollPane Methods

Studying That Suits You

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What is the relationship between `EventObject` and `AWTEvent` in the Java event handling hierarchy?

Which of the following scenarios would typically result in an `ActionEvent`?

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?

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?

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 `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 `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`?

Which method in the `ItemEvent` class provides information about the change in an item's state?

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?