Java Programming Fourth Edition - Rutgers Universityszhou/351/ch14.pdf · 2009. 11. 24. · Java...

Java Programming Fourth Edition

Chapter 14 Using Layout Managers and Events

Java Programming, Fourth Edition 2

Objectives

•  Learn about layout managers •  Use JPanels to increase layout options •  Understand events and event handling •  Use the AWTEvent class methods •  Handle mouse events


Learning About Layout Managers

•  Layout manager –  Controls size and position of Components inside a Container object

–  Assign to content pane or panel –  Interface classes –  Part of Java SDK –  Align components so that they don’t:

•  Crowd each other •  Overlap


Learning About Layout Managers (continued)

•  Layout manager (continued) –  Arrange components within a Container –  Container can also be Container itself –  Assign layout managers within layout managers

•  Java platform-supplied layout managers –  FlowLayout and GridLayout –  BorderLayout and CardLayout –  GridBagLayout and BoxLayout


Java Layout Managers


Using BorderLayout

•  BorderLayout manager –  Default for all content panes –  Use with:

•  Container with five or fewer components •  Component containers can hold more components

–  Fill screen in regions •  North •  South •  East •  West •  Center


The JDemoBorderLayout Application


Using BorderLayout (continued)

•  Static import feature –  Allows static constant without class name import static java.awt.BorderLayout.*;

•  GUI component must be part of: –  Containment hierarchy

•  Tree of components •  Top-level container as its root


Using BorderLayout (continued)

•  Create Container named con –  Set layout manager to BorderLayout con.setLayout(new BorderLayout());

•  To set layout manager setLayout(new BorderLayout()); Or this.setLayout(new BorderLayout());

•  Place object in south region of JApplet’s Container add(someButton, BorderLayout.SOUTH)


Using FlowLayout

•  FlowLayout manager –  Arrange components in rows across width of Container

–  Add Component •  Place to right of previously added components in row •  If current row filled Component placed to start new

row –  Each Component retains preferred size


Using FlowLayout (continued) •  Align Components with Container

FlowLayout.LEFT

FlowLayout.CENTER FlowLayout.RIGHT

–  If alignment not specified • Components center-aligned


The JDemoFlowLayout Applet


Using FlowLayout (continued) •  invalidate()

–  Marks container as needing to be laid out •  validate()

–  Causes components to be rearranged based on newly assigned layout


Using GridLayout

•  GridLayout manager class –  Arrange components into equal rows and columns

•  Create GridLayout object –  Indicate numbers of rows and columns

•  Specify rows first and then columns –  Container surface divided into grid

•  Establish GridLayout con.setLayout(new GridLayout(4, 5));


Using GridLayout (continued)

•  Establish GridLayout within JApplet this.setLayout(new GridLayout(4, 5));

Or setLayout(new GridLayout(4, 5)); •  Establish GridLayout with three horizontal rows,

two vertical columns, and vertical gaps of five pixels each private GridLayout layout = new GridLayout(3, 2, 5, 5);

•  Can use 0 for number of columns or rows


The JDemoGridLayout Applet


Output of the JDemoGridLayout Applet


Using CardLayout

•  CardLayout manager –  Generates stack of containers or components –  One on top of another –  Each component in group referred to as card –  Multiple components share same display space


Using CardLayout (continued)

•  Create card layout with one of two constructors CardLayout()

•  Creates card layout without horizontal or vertical gap CardLayout(int hgap, int vgap)

•  Creates card layout with specified horizontal and vertical gaps

–  Add component to content pane add(aString, aContainer);


The JDemoCardLayout JApplet


Using Advanced Layout Managers

•  GridBagLayout manager –  Add Components to precise locations within grid –  Indicate specific Components should span multiple

rows or columns within grid –  Must set position and size for each component –  Must customize one or more GridBagConstraints

objects •  BoxLayout manager

–  Allows multiple components to be laid out either vertically or horizontally


Using JPanels to Increase Layout Options

•  Using JPanels within JPanels can create infinite variety of screen layouts

•  Create JPanel object –  Constructors

JPanel()

JPanel(LayoutManager layout)

JPanel(Boolean isDoubleBuffered) JPanel(LayoutManager layout, Boolean isDoubleBuffered)


Output of the Checkerboard Application


Understanding Events and Event Handling

•  Events –  Objects that user initiates

•  EventObject –  Parent class for all event objects –  Descends from Object class –  Parent of AWTEvent class

•  Parent of ActionEvent and ComponentEvent


The Inheritance Hierarchy of Event Classes


Understanding Events and Event Handling (continued)

•  ActionEvents –  Focus on changes in a component

•  MouseEvents –  Focus on what user does manually with mouse

•  Computer’s operating system notifies user when AWTEvent occurs –  Can ignore AWTEvents –  Must implement appropriate interface for your class

•  To receive events


Examples of User Actions and Their Resulting Event Types



•  Event handler –  Interface method such as actionPerformed() –  Called automatically when appropriate event occurs

•  Adapter class –  Implements all methods in an interface

•  Provides empty body for each method

•  Extend adapter class –  Write only methods you want to use

•  Don’t bother creating empty methods for others



•  Create event handler –  When writing code for listener methods

•  Tell class how to handle events •  Register instance of class with component that

event affects –  For any <name>Listener object.add<name>Listener(Component)


An Event-Handling Example: KeyListener

•  KeyListener interface –  Receive actions user initiates from keyboard

•  KeyListener contains three methods: keyPressed()

keyTyped() •  Discover which character was typed •  Does not execute calls from action keys

keyReleased() •  Does not take action while user holds down key


Events with Their Related Listeners and Handlers


An Event-Handling Example: KeyListener (continued)

•  KeyEvent class –  Contain virtual key codes

•  Represent keyboard keys that have been pressed •  Virtual key code constants have names such as

VK_SHIFT and VK_ALT


Using AWTEvent Class Methods

•  AWTEvent classes –  Contain methods

•  Determine nature of and facts about event –  All Components define methods

• addComponentListener() • addFocusListener() • addMouseListener() • addMouseMotionListener()


Using AWTEvent Class Methods (continued)

•  Call Event class methods –  Use object-dot-method format

• InputEvent named inEvent and integer named modInt

modInt = inEvent.getModifiers();

•  Use event object within handler method to obtain information –  Add dot and appropriate method name

•  Use any methods that belong to any superclass of an event


Useful Event Class Methods


Handling Mouse Events

•  MouseMotionListener interface: mouseDragged() and mouseMoved()

•  Detect mouse being rolled or dragged across component surface

•  MouseListener interface: mousePressed(), mouseClicked(), and mouseReleased()

•  Analogous to keyboard event methods mouseEntered() and mouseExited()

•  User positions mouse over component (entered) •  Or moves mouse off component (exited)


MouseListener Methods


MouseMotionListener Methods


Handling Mouse Events (continued)

•  MouseInputListener interface –  Implements all methods in both MouseListener

and MouseMotionListener interfaces –  Has no methods of its own –  Handles many different types of mouse events

•  MouseEvent –  Type of event generated by mouse manipulation –  Contains instance methods and fields

•  Useful in describing mouse-generated events


The Inheritance Hierarchy of the MouseEvent Class


You Do It

•  Using BorderLayout •  Using fewer than five components with the BorderLayout manager

•  Using FlowLayout •  Using CardLayout •  Viewing all the cards in CardLayout


You Do It (continued)

•  Using JPanels to achieve complex layouts •  Implementing KeyListener •  Using the getSource() method to determine an

event •  Using MouseEvents


Summary

•  Layout manager –  Object that controls size and position of components

inside a Container object –  BorderLayout –  FlowLayout –  GridLayout –  CardLayout –  GridBagLayout

•  Use JPanels within other JPanels –  Create infinite variety of screen layouts


Summary (continued)

•  Events are Objects that user initiates •  Implement appropriate listener interface for your

class •  Event handlers

–  Interface methods automatically called when event occurs

•  KeyListener interface –  Handles keyboard events

•  MouseListener interface –  Handles mouse events

Java Programming Fourth Edition - Rutgers Universityszhou/351/ch14.pdf · 2009. 11. 24. · Java...

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