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

Java Programming, Fourth Edition 3

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

Java Programming, Fourth Edition 4

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 Programming, Fourth Edition 5

Java Layout Managers

Java Programming, Fourth Edition 6

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

Java Programming, Fourth Edition 7

The JDemoBorderLayout Application

Java Programming, Fourth Edition 8

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

Java Programming, Fourth Edition 9

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)

Java Programming, Fourth Edition 10

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

Java Programming, Fourth Edition 11

Using FlowLayout (continued) •  Align Components with Container

FlowLayout.LEFT

FlowLayout.CENTER FlowLayout.RIGHT

–  If alignment not specified • Components center-aligned

Java Programming, Fourth Edition 12

The JDemoFlowLayout Applet

Java Programming, Fourth Edition 13

Using FlowLayout (continued) •  invalidate()

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

–  Causes components to be rearranged based on newly assigned layout

Java Programming, Fourth Edition 14

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));

Java Programming, Fourth Edition 15

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

Java Programming, Fourth Edition 16

The JDemoGridLayout Applet

Java Programming, Fourth Edition 17

Output of the JDemoGridLayout Applet

Java Programming, Fourth Edition 18

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

Java Programming, Fourth Edition 19

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);

Java Programming, Fourth Edition 20

The JDemoCardLayout JApplet

Java Programming, Fourth Edition 21

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

Java Programming, Fourth Edition 22

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)

Java Programming, Fourth Edition 23

Output of the Checkerboard Application

Java Programming, Fourth Edition 24

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

Java Programming, Fourth Edition 25

The Inheritance Hierarchy of Event Classes

Java Programming, Fourth Edition 26

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

Java Programming, Fourth Edition 27

Examples of User Actions and Their Resulting Event Types

Java Programming, Fourth Edition 28

Understanding Events and Event Handling (continued)

•  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

Java Programming, Fourth Edition 29

Understanding Events and Event Handling (continued)

•  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)

Java Programming, Fourth Edition 30

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

Java Programming, Fourth Edition 31

Events with Their Related Listeners and Handlers

Java Programming, Fourth Edition 32

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

Java Programming, Fourth Edition 33

Using AWTEvent Class Methods

•  AWTEvent classes –  Contain methods

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

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

Java Programming, Fourth Edition 34

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

Java Programming, Fourth Edition 35

Useful Event Class Methods

Java Programming, Fourth Edition 36

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)

Java Programming, Fourth Edition 37

MouseListener Methods

Java Programming, Fourth Edition 38

MouseMotionListener Methods

Java Programming, Fourth Edition 39

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

Java Programming, Fourth Edition 40

The Inheritance Hierarchy of the MouseEvent Class

Java Programming, Fourth Edition 41

You Do It

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

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

Java Programming, Fourth Edition 42

You Do It (continued)

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

event •  Using MouseEvents

Java Programming, Fourth Edition 43

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

Java Programming, Fourth Edition 44

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