Java Programming, Second Edition

1
Java Programming, Second Edition

• Chapter Fourteen
• Using Layout Managers and the Event Model

2
In this chapter, you will

• Learn about layout managers
• Use JPanels
• Learn about advanced layout managers
• Understand events and event handling
• Use the AWTEvent class methods
• Use event methods from higher in the inheritance
  hierarchy
• Handle mouse events

3
Learning about Layout Managers

• Layout manager- An interface class that is part
  of the JDK
• Aligns your components so they neither crowd each
  other nor overlap
• Can assign layout managers within layout managers
• For example
• One layout manager arranges components in equally
  spaced columns and rows

4
Learning about Layout Managers
5
Learning about Layout Managers

• BorderLayout manager- The default manager for all
  content panes
• Can use the BorderLayout class with any container
  that has five or fewer components
• Components fill the screen with five regions
  named North, South, East, West, and Center
• The compiler determines the exact size of each
  component based on the components contents
• When BorderLayout is used with less than five
  components, any empty regions disappear

6
Positions using the BorderLayout
7
Learning about Layout Managers

• FlowLayout- To arrange Components in rows across
  the width of a container
• Each component retains its default size
• Each component that you add is placed to the
  right of previously added components

8
Learning about Layout Managers

• GridLayout- To arrange Components into equal rows
  and columns
• You indicate the numbers of rows and columns you
  want, and then the container surface is divided
  into a grid
• Specify rows first, columns second
• As you add components they are positioned
  left-to-right across each row in sequence

9
JDemoGrid Swing applet
10
Learning about Layout Managers

• CardLayout- Generates a stack of containers or
  components, one on top of another
• Each container in the group is referred to as a
  card
• Only one component is visible at a time
• A card layout is created from the CardLayout
  class using one of two constructors
• CardLayout() creates a new card layout without a
  horizontal or vertical gap
• CardLayout(int hgap, int vgap) creates a new card
  layout with the specified horizontal and vertical
  gaps

11
Using JPanels

• JPanels- Increase the number of possible
  component arrangements by using the JPanel class
• A JPanel is similar to a JWindow in that a JPanel
  is a surface on which you can place components
• JPanel is a Container so it can contain other
  components
• By using JPanels within JPanels, you can create
  an infinite variety of screen layouts

12
Using JPanels

• JPanel object constructors
• JPanel() creates a new JPanel with a double
  buffer and a flow layout
• JPanel(LayoutManager layout) creates a new
  buffered JPanel with the specified layout manager

13
Learning about Advanced Layout Managers

• GridBagLayout- Allows you to add components to
  precise locations within the grid, as well as to
  indicate that specific Components should span
  multiple rows or columns within the grid
• This class is difficult to use because you must
  set the position and size for each component

14
Learning about Advanced Layout Managers

• BoxLayout- Components are arranged in either a
  single row or a single column
• The box layout manager tries to make all the
  components the same height(row) or width(column)
  so components do not spill over

15
BoxLayout

• Requires two arguments
• The first refers to the container to which the
  layout manager applies
• The second is a constant
• BoxLayout.X_Axis for a row arrangement
• BoxLayout.Y_Axis for a column arrangement

16
Understanding Events and Event Handling

• Events are Objects that the user initiates
• For example a mouse click or a key press
• The parent class for all event objects is
  EventObject
• Event object descends from the Object class
• EventObject is the parent class to AWTEvent which
  is the parent to specific classes such as
  ActionEvent

17
Understanding Events and Event Handling
18
Understanding Events and Event Handling

• When you want to listen for an event, you can
  implement an appropriate interface for the class
  such as ActionListener or Window Listener
• The class becomes an event listener
• For every event class there is a similarly named
  listener
• Every ltnamegt listener interface method has a
  return type of void, and each takes one argument

19
Understanding Events and Event Handling

• Event handlers- Interface methods, such as
  actionPerformed(), that are called automatically
  when an appropriate event occurs

20
Understanding Events and Event Handling
21
Understanding Events and Event Handling
22
Understanding Events and Event Handling

• The KeyListener interface- Used when you are
  interested in events that users initiate from the
  keyboard
• keyPressed()- provides information about keys
  that dont generate characters
• keyTyped()- provides information about what key
  was typed
• keyReleased()- provides information about keys
  that dont generate characters

23
Using AWTEvent Class Methods

• AWTEvent Class methods- Use many of these methods
  to determine the nature of and the facts about an
  event in question
• The AWTEvent classes themselves contain methods

24
Using Event Methods from Higher in the
Inheritance Hierarchy

• When you use an event such as KeyEvent, you can
  use any of the events methods
• Because of inheritance, you can also use methods
  that belong to any class that is a superclass of
  the event with which you are working

25
Handling Mouse Events

• When you write GUI programs, you probably expect
  users to spend most of their time operating a
  mouse
• You are interested in more than key presses
• The MouseListener interface provides you with
  methods

26
Mouse Events

• mouseDragged()
• mouseMoved()
• mousePressed()
• mouseClicked()
• mouseReleased()
• mouseEntered()
• mouseExited()