Swings Listeners and Layout

8/10/2019 Swings Listeners and Layout

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ETIT-303CSE 5thSemester

Lecture 14


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A layout manager allows the java programmer to develop graphicalinterfaces that will have a common appearance across theheterogeneous internet.

There are five layout managers that the programmer may choosefrom:

Flow Layout

Grid Layout

Border Layout

Card Layout

Gridbag Layout


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Object

Component

ButtonTextComponent

Checkbox ChoiceContainer

Label

TextArea TextField

ScrollBarCanvas

Panel ScrollPaneWindow

Part of the AWT Class Hierarchy

Dialog Frame

Applet

List


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Layout Managers

A Component can be displayed on a screen and a user caninteract with a Component.

A Container is a Component that can hold other Components

A Layout Manager directs the placement of Componentswithin a Container.


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A Containermaintains a list of Components that it manipulates as wellas a LayoutManagerto determine how components are displayed.

The Container class contains the following subclasses:

Window

Frame

Dialog

Panel

Applet

ScrollPane


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Containers

Method defined in class Container include:

setLayoutManager (LayoutManager)

add (Component) add Component to display

remove(Component) remove Component from display


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Containers

Window

A Window is a 2-dimensional drawing surface that can be displayedon an output device.

A Window can be stacked on top of other Windows and can bemoved to the front or back of the visible windows.

Methods in class Window include:

show ( ) Make the Window visible

toFront( ) Move Window to front

toBack( ) Move window to back


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Frame

A Frame is a type of Window with a title bar, a menu bar, a border, and acursor. It is used most frequently to display applicationsthat contain agraphical user interface or an animation.

Methods defined in Frame include:

setTitle(String) getTitle(String)

setCursor(int)

setResizable( ) make the window resizable

setMenuBar(MenuBar) include the menu bar for the window


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Containers

Panel

A Panel is generally used as a component in a Frame or anApplet.

It is used to group components into a single unit. The Panel with

its set of components is displayed as a single unit. It represents arectangular region of the display.

A Panelholds its own LayoutManager which may be different from theLayoutManager of the Frame or Applet in which it resides.


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Dialog

Always attached to an instance of Frame.

A window that is displayed for a short duration during execution.

Default LayoutManager is BorderLayoutManager (same asfor Frame)

ScrollPane

It can hold only one Component.

It does not have a LayoutManager.

If size of the component held is larger than the size of the ScrollPane,scroll bars will be automatically generated.


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Layout Managers

Flow Layout

Lays out components row by row from left to right.

As an example, consider an applet (subclass of Panel) that displays a

number of Buttons for selecting a language.

It is very straightforward to use, but it affords the programmer the

least ability to control the positioning of components. It is thedefault layout manager in an applet.


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Layout Managers

English French Greek

Japanese German

Spanish Portuguese

Arabic Chinese Russian

Applet Started


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Layout Managers

Constructing the previous display

importjava.awt.*;

publicclass SelectLang extends java.applet.Applet {

Button eng = newButton(English);

.

Button rus = newButton (Russian);

FlowLayout flow = new FlowLayout(FlowLayout.LEFT);

publicvoid init ( ) {

setLayout(flow);

add(eng);

.

add(rus);

}

}


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Layout Managers

Suppose we wish to construct the following layout

Age 21-35 Over 65Under 20 36-65

Name

Street Address

City Zip


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Layout Managers

FlowLayout (intalignment, inthGap, intvGap);

In Example 1 FlowLayout(FlowLayout.LEFT, 30, 10)

A more orderly organization is achieved by first putting componentsinto panels and then placing panels in applet using Flow Layout


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Layout Managers

Border Layout

North

South

CenterWest East


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Layout Managers

Properties of a Border Layout Manager

More flexible in permitting programmer placement of components ofdifferent sizes (such as panels, canvases and text areas.

Border areas adjust to accommodate the placement of a component.The center consists of whats left over.

publicBorderLayout (inthGap, intvGap)


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Layout Managers

Example

A BorderLayout with a Label in North, a Scrollbar in South,a Panel containing a Checkboxgroup in West, a List in East, and aCanvas in Center.

Border Layout Example

Rectangle

Oval

Line

Fill

Background

o Redo Blueo Green

o Blacko White


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Layout Managers

Grid Layout

Programmer specifies the number of

rows

columns

pixels between rows, pixels between columns

GridLayout myGrid = new GridLayout (3, 2, 10, 10);


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Layout Managers

Grid Layout

Components expand or contract in size to fill a single gridcell. Panels, canvases, and Lists are resized to fit into a grid

cell.

Components are placed in the container in order from left to rightand top to bottom.


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Layout Managers

Grid Layout

name

address

e-mail


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Layout Managers

Card Layout

A card layout is a group of components orcontainers that are displayed one at a time.

Components or containers are placed on a card using thestatement:

add (String, component);


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Layout Managers

Card Layout Construction

The Applet contains an ordered listing (array) of cards inone of its panels

Card Panel


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Layout Managers

Applet Declarations

public classCardDemo extendsApplet {privatefinal intnumCards = __; //whatever the number

privateString[ ] = newCardLabels[numCards];

//construct an array for holding CardPanel objects specified in separate file

privateCardPanel[ ] cards = newCardPanel[numCards];

privateCardLayout theLayout; //Layout for CardPanels//Create a Panel for displaying CardPanel objects in the Applet (green area)

privatePanel cardDisplayPanel;

Applet initialization

public void init ( ) {

//essential statements for card display

setLayout (newBorderLayout); //layout for the Applet

add(West, makeOtherPanel( )); //2ndparameter returns a Panel

add(Center, makeCardDisplayPanel( )); //2ndparam returns a Panel

}


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Layout Managers

CardPanel Objects

CardPanelsare containers with their own Components and

Layout

CardPanelis a separately declared class that extends Panel

CardPanelobjects are created in method makeCardDisplayPanel() ofApplet

CardPanelobjects are stored in the array cards


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Java provides two sets of facilities for developing GUIs:

The Abstract Window Toolkit (AWT): package java.awt Swing: package javax.swing

Swing architecture is rooted in the model-view-controller( MVC) design that dates back to SmallTalk .MVC architecture calls for a visual application to be brokenup into three separate parts:

A modelthat represents the data for the application.

The viewthat is the visual representation of that data.

A controllerthat takes user input on the view andtranslates that to changes in the model.


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Text-based interface Predetermined

sequence of events The program pauses

execution when itexpects input from theuser and continues onthe same set path after

it receives the input

Graphical interface No set sequence of

events The user can do any

number of things atany time (type in a textbox, resize thewindow, press abutton)

These responses arecalled events. We say the program is

event-driven.


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AWTAWT stands for Abstract windowstoolkit.

AWT components are calledHeavyweight component.

AWT components require java.awtpackage.

AWT components are platformdependent. This feature is not supported in

AWT.

SWING Swing is also called as JFCs(Java Foundation classes). Swings are called light weight component because swing

components sits on the top of AWT components and do the work. Swing components require javax.swing package. Swing components are made in purely java and they are platform

independent. We can have different look and feel in Swing.These feature is not

available in AWT.Swing has many advanced features like JTabel,Jtabbed pane which is not available in AWT. Also. Swingcomponents are called "lightweight" because they do not require anative OS object to implement their functionality. JDialog andJFrame are heavyweight, because they do have a peer. Socomponents like JButton, JTextArea, etc., are lightweight becausethey do not have an OS peer.

With Swing, you would have only one peer, the operating system'swindow object. All of the buttons, entry fields, etc. are drawn by theSwing package on the drawing surface provided by the windowobject. This is the reason that Swing has more code. It has to drawthe button or other control and implement its behavior instead ofrelying on the host operating system to perform those functions.

Swing is much larger. Swing also has very much richer functionality.


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INE2720 Web ApplicationSoftware Development All copyrights reserved by C.C. Cheung 2003. 29

Constructors

These three constructors apply to checkboxes that operateindependentlyof each other (i.e., not radio buttons)

Checkbox()

Creates an initially unchecked checkbox with no label

Checkbox(String checkboxLabel)

Creates a checkbox (initially unchecked) with the specified label; seesetStatefor changing it

Checkbox(String checkboxLabel, boolean state) Creates a checkbox with the specified label

The initial state is determined by the boolean value provided

A value of true means it is checked


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public class Checkboxes extends CloseableFrame {public Checkboxes() {super("Checkboxes");setFont(new Font("SansSerif", Font.BOLD,18));

setLayout(new GridLayout(0, 2));Checkbox box;for(int i=0; i


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getState/setState

Retrieves or sets the state of the checkbox: checked (true)or unchecked (false)

getLabel/setLabel Retrieves or sets the label of the checkbox

After changing the label invalidate and validate thewindow to force a new layout (same as button).

addItemListener/removeItemListener Add or remove an ItemListenerto process

ItemEvents in itemStateChanged


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CheckboxGroup Constructors

CheckboxGroup()

Creates a non-graphical object used as a tagto group checkboxes

logically together Only one checkbox associated with a particular tag can be selected

at any given time

Checkbox Constructors

Checkbox(String label, CheckboxGroup group,boolean state)

Creates a radio button associated with the specified group, with thegiven label and initial state


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import java.applet.Applet;import java.awt.*;

publicclass CheckboxGroups extends Applet {publicvoid init() {setLayout(new GridLayout(4, 2));

setBackground(Color.lightGray);setFont(new Font("Serif", Font.BOLD, 16));add(new Label("Flavor", Label.CENTER));add(new Label("Toppings", Label.CENTER));CheckboxGroup flavorGroup = new CheckboxGroup();add(new Checkbox("Vanilla", flavorGroup, true));add(new Checkbox("Colored Sprinkles"));add(new Checkbox("Chocolate", flavorGroup, false));add(new Checkbox("Cashews"));add(new Checkbox("Strawberry", flavorGroup, false));add(new Checkbox("Kiwi"));

}}


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Constructors List(int rows, boolean multiSelectable)

Creates a listbox with the specified number of visible rows

Depending on the number of item in the list (addItem or add), ascrollbar is automatically created

The second argument determines if the List is multiselectable

List() Creates a single-selectable list box with a platform-dependent

number of rows and a platform-dependent width

List(int rows) Creates a single-selectable list box with the specified number of

rows and a platform-dependent width


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import java.awt.*;

public class Lists extends CloseableFrame {public Lists() {super("Lists");setLayout(new FlowLayout());setBackground(Color.lightGray);setFont(new Font("SansSerif", Font.BOLD, 18));

List list1 = new List(3, false);list1.add("Vanilla");list1.add("Chocolate");list1.add("Strawberry");add(list1);List list2 = new List(3, true);list2.add("Colored Sprinkles");list2.add("Cashews");list2.add("Kiwi");add(list2);pack();setVisible(true);

}}

A list can be single-selectable or multi-selectable


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EVENT HANDING


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A source generates an event and sends it toone or more listeners.

The listener simply waits until it receives anevent. Listener must register with source to receive

noticification.


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-An event is an object that describes a statechange in a source.

-It can be generated as a consequence of a

person interacting with the elements in agraphical user interface.

Examples.Pressing a button, entering a character via thekeyboard, selecting an item in a list, andclicking the mouse, timer expires, counter,h/w or s/w failure.


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A source is an object that generates an event.

This occurs when the internal state of that

object changes.

A source must register listeners.

public void addTypeListener(TypeListener el)

e.g. public void addKeyListener()


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public void addTypeListener(TypeListener el)throwsjava.util.TooManyListenersException

public void removeTypeListener(TypeListener el)


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A listener is an object that is notified when anevent occurs.

It must register with one or more sources.

It must implement methods to receive andprocess these notifications.


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EventObject(java.util)

AWTEvent(java.awt)


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EventObject contains two methods:getSource( ) and toString()

The getSource( ) method returns the source

of the event.

general form : Object getSource( )

-The class AWTEvent, defined within thejava.awt package which is a sub class ofEventObject.

-AWTEvent is a su erclass of all AWT events


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Listeners are created by implementing one ormore of the interfaces defined by the

java.awt.event package.

When an event occurs, the event source invokes

the appropriate method defined by the listenerand provides an event object as its argument.


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void actionPerformed(ActionEvent ae)


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Void adjustmentValueChanged(AdjustmentEvent ae)


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void componentResized(ComponentEvent ce)

void componentMoved(ComponentEvent ce)

void componentShown(ComponentEvent ce)

void componentHidden(ComponentEvent ce)


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void componentAdded(ContainerEvent ce)Void componrntListener(ContainerEvrnt ce)

void componentRemoved(ContainerEvent ce)


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void focusLost(FocusEventfe)

void focusGained(FocusEventfe)


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void itemStateChanged(ItemEvent ie)


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void keyPressed(KeyEvent ke)

void keyReleased(KeyEvent ke)

void keyTyped(KeyEvent ke)


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void mouseClicked(MouseEvent me)void mouseEntered(MouseEvent me)void mouseExited(MouseEvent me)void mousePressed(MouseEvent me)void mouseReleased(MouseEvent me)


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void mouseDragged(MouseEvent me)void mouseMoved(MouseEvent me)


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void textChanged(TextEvent te)


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void windowGainedFocus(WindowEvent we)

void windowLostFocus(WindowEvent we)


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void windowActivated(WindowEvent we)void windowClosed(WindowEvent we)void windowClosing(WindowEvent we)

void windowDeactivated(WindowEventwe

)void windowDeiconified(WindowEvent we)void windowIconified(WindowEvent we)void windowOpened(WindowEvent we)


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void menuCanceled(MenuEvente) void menuDeselected(MenuEvente) void menuSelected(MenuEvente)
http://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuListener.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuListener.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuListener.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuEvent.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuEvent.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuListener.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuEvent.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuEvent.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuEvent.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuEvent.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuListener.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuEvent.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuListener.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuEvent.htmlhttp://docs.oracle.com/javase/7/docs/api/javax/swing/event/MenuListener.html

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Swings Listeners and Layout