CS3340: Swing and CS3340: Swing and Event handlingEvent handling

L. GreweL. Grewe

SwingDifferences between Swing and AWT

Naming Conventions

All Swing components begin with a capital J -- JPanel, JButton, JScrollBar, JApplet, etc..

Most Swing Components are “Lightweight”

•Use Java code rather than native code to draw in the underlying window.

•The Exceptions are JFrame, JApplet, JWindow, and JDialog

Use Content Pane for adding Components to “Heavyweight” Containers

To add Components to a JApplet (in method init( )) use

Container cp = new getContentPane( );

cp.add(new JButton(“Start”);

SwingDifferences between Swing and AWT Components

Use of paintComponent for Drawing

public void paintComponent(Graphics g) {

super.paintComponent(g);

//always call super.paintComponent( ) before performing custom drawing

// draw Shape on the Swing Component

}Double Buffering

In Swing a JPanel is used instead of a Canvas to be the target for drawing graphics objects. When drawing to a JPanel using paintComponent double buffering is automatically employed. There is an option to perform drawing directly to the screen using the paint method by using panel.getGraphics( );

Anatomy of a Java Swing GUIAnatomy of a Java Swing GUI JFrameJFrame JPanelJPanel Layout ManagerLayout Manager JComponentsJComponents

JPanel

JButton

JFrame

Layout Manager

Build from bottom upBuild from bottom up

Create:Create: FrameFrame PanelPanel Layout managerLayout manager ComponentsComponents ListenersListeners

Add: (bottom up)Add: (bottom up) layout manager to panel layout manager to panel listeners to componentslisteners to components components to panelcomponents to panel panel to framepanel to frame

JPanel

JButton

Layout

Listener

JFrame

CodeCode

JFrame f = new JFrame(“title”)JFrame f = new JFrame(“title”)

JPanel p = new JPanel( );JPanel p = new JPanel( );

JButton b = new JButton(“press me”);JButton b = new JButton(“press me”);

p.add(b);p.add(b); // add button to // add button to panelpanel

f.setContentPane(p); // add panel to framef.setContentPane(p); // add panel to frame

f.setVisible(true);f.setVisible(true);

General-Purpose ContainersGeneral-Purpose Containers

Intermediate containers which can Intermediate containers which can be used under many different be used under many different circumstances:circumstances:• Panel (JPanel)Panel (JPanel)• Scroll pane (JScrollPane)Scroll pane (JScrollPane)• Split paneSplit pane• Tabbed paneTabbed pane• Tool barTool bar

General Purpose Containers General Purpose Containers PanelPanel—most flexible and frequently —most flexible and frequently

used. Add almost no functionality used. Add almost no functionality beyond what all objects have. Often beyond what all objects have. Often used to group components.used to group components.

Scroll paneScroll pane—provides scroll bars —provides scroll bars around a large or growable around a large or growable component.component.

Split paneSplit pane—displays two —displays two components in a fixed amount of components in a fixed amount of space, letting the user adjust the space, letting the user adjust the amount of space devoted to each amount of space devoted to each component.component.

General Purpose Containers General Purpose Containers

Tabbed paneTabbed pane—contains —contains multiple components but show multiple components but show only one at a time. The user only one at a time. The user can easily switch between can easily switch between components.components.

Tool barTool bar—holds a group of —holds a group of components (usually buttons) components (usually buttons) in a row or column, optionally in a row or column, optionally allowing the user to drag the allowing the user to drag the tool bar into different locations.tool bar into different locations.

General-Purpose ContainersGeneral-Purpose Containers

Panel

Scroll Pane

Tool bar

Split pane

Tabbed pane

Special-Purpose ContainersSpecial-Purpose Containers Intermediate containers that play Intermediate containers that play

specific roles in the use interface. specific roles in the use interface. • Internal frameInternal frame— Able to display display — Able to display display

a Frame-like window within another a Frame-like window within another window. Usually, you add internal frames window. Usually, you add internal frames to a desktop pane.to a desktop pane.

• Layered frameLayered frame—Provides a third —Provides a third dimension for positioning components: dimension for positioning components: depth, also known as Z order.depth, also known as Z order.

• Root paneRoot pane—Has 4 parts: glass pane, —Has 4 parts: glass pane, layered pane, content pane, layered pane, content pane, and the (optional) menu bar. and the (optional) menu bar.

Special-Purpose ContainersSpecial-Purpose Containers

Internal Frame

Layered Pane

Root Pane

Layout ManagersLayout Managers Review -layout managers:Review -layout managers:

null (no manager, programmer sets x,y,w,h)null (no manager, programmer sets x,y,w,h) FlowlayoutFlowlayout GridLayoutGridLayout BorderLayoutBorderLayout

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n

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ew

CodeCode

JFrame f = new JFrame(“title”)JFrame f = new JFrame(“title”)

JPanel p = new JPanel( );JPanel p = new JPanel( );

JButton b = new JButton(“press me”);JButton b = new JButton(“press me”);

b.setBounds(new Rectangle(10,10, 100,50));b.setBounds(new Rectangle(10,10, 100,50));

p.setLayout(null);p.setLayout(null); // x,y layout// x,y layout

p.add(b);p.add(b);

f.setContentPane(p);f.setContentPane(p);

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An example nested layoutAn example nested layout Container container = new Container container = new JFrame() or JApplet()JFrame() or JApplet();;

JPanel p1 = new JPanel(); JPanel p1 = new JPanel(); p1.setLayout(new BorderLayout());p1.setLayout(new BorderLayout());p1.add(new JButton("A"), BorderLayout.NORTH);p1.add(new JButton("A"), BorderLayout.NORTH); // also add buttons B, C, D, E // also add buttons B, C, D, E

JPanel p2 = new JPanel();JPanel p2 = new JPanel();p2.setLayout(new GridLayout(3, 2));p2.setLayout(new GridLayout(3, 2));p2.add(new JButton("F"));p2.add(new JButton("F")); // also add buttons G, H, I, J, K // also add buttons G, H, I, J, K

JPanel p3 = new JPanel();JPanel p3 = new JPanel();p3.setLayout(new BoxLayout(p3, BoxLayout.Y_AXIS));p3.setLayout(new BoxLayout(p3, BoxLayout.Y_AXIS));p3.add(new JButton("L"));p3.add(new JButton("L")); // also add buttons M, N, O, P // also add buttons M, N, O, P

container.setLayout(new BorderLayout()); container.setLayout(new BorderLayout()); container.add(p1, BorderLayout.CENTER); container.add(p1, BorderLayout.CENTER); container.add(p2, BorderLayout.SOUTH); container.add(p2, BorderLayout.SOUTH); container.add(p3, BorderLayout.EAST); container.add(p3, BorderLayout.EAST);

ComponentsComponents• Buttons—Buttons—can be square or roundcan be square or round

• Combo BoxCombo Box—can be uneditable and editable.—can be uneditable and editable.• ListList—Presents the user with a group of items, —Presents the user with a group of items,

displayed in a column, to choose from. displayed in a column, to choose from. • MenuMenu—provides a space-saving way to let the —provides a space-saving way to let the

user choose one of several options.user choose one of several options.• SliderSlider—lets user enter a numeric value —lets user enter a numeric value

bounded by a minimum and maximum value.bounded by a minimum and maximum value.• Text FieldsText Fields—basic text control that lets the —basic text control that lets the

user enter a small amount of text.user enter a small amount of text.

Basic ComponentsBasic Components

Buttons Combo BoxList

Menu Slider Text Fields

More Components – not More Components – not selectableselectable

Atomic components that exist solely to give Atomic components that exist solely to give the user information. the user information. • LabelLabel—able to display unselectable text and —able to display unselectable text and

images.images.

• Progress BarProgress Bar—displays the progress of a long-—displays the progress of a long-running task (also, ProgressMonitor and running task (also, ProgressMonitor and ProgressMonitorInputStream)ProgressMonitorInputStream)

• Tool tipTool tip—comes up when the user of the —comes up when the user of the program pauses with the cursor over any of the program pauses with the cursor over any of the program's buttonsprogram's buttons

Uneditable Information Uneditable Information DisplaysDisplays

Tool Tips

Progress Bar

Label

Editable Displays of Formatted InformationEditable Displays of Formatted Information Atomic components that display highly formatted Atomic components that display highly formatted

information that can be edited by the user. information that can be edited by the user.

• Color chooser—Color chooser—provide users with a palette provide users with a palette of colors to choose from.of colors to choose from.

• File chooser—File chooser—provide a GUI for navigating provide a GUI for navigating the file system, and then either choosing a the file system, and then either choosing a file or directory from a list or entering a file file or directory from a list or entering a file name or directory name.name or directory name.

• Table—Table—displays tables of data, optionally displays tables of data, optionally allowing the user to edit the data. allowing the user to edit the data.

• Text—Text—displays text and allows user to edit itdisplays text and allows user to edit it• Tree—Tree—displays data in hierarchical waydisplays data in hierarchical way

Editable Displays of Editable Displays of Formatted InformationFormatted Information

File Chooser

Color Chooser

Table Text

Tree

EventsEvents

How to handle user events related to How to handle user events related to GUI componentsGUI components

EventsEvents Register with a component to receive Register with a component to receive

eventsevents Give component a ref to a Listener objectGive component a ref to a Listener object

ActionListenerActionListener KeyListenerKeyListener MouseListenerMouseListener WindowListenerWindowListener ……

JButton

Listener

click

ActionEventregister

CodeCode

myListener = new myListenClass;myListener = new myListenClass;

btn.addActionListener(myListener);btn.addActionListener(myListener);

Class myListenClass implements ActionListener {Class myListenClass implements ActionListener {

public void actionPerformed(ActionEvent e){public void actionPerformed(ActionEvent e){

// button pressed, do stuff here// button pressed, do stuff here

}}

}}

Simplifying: InheritanceSimplifying: Inheritance

Class myframe Class myframe extendsextends JFrame{ JFrame{

public myframe(){public myframe(){

// create panel, buttons, …// create panel, buttons, …

setContentPane(p); // I am a jframesetContentPane(p); // I am a jframe

}}

public static void main(){public static void main(){

JFrame f = new myframe();JFrame f = new myframe();

}}

}}

Myframe creates JFrame via inheritanceMyframe creates JFrame via inheritance

Simplifying: InheritanceSimplifying: InheritanceClass myframe extends JFrame{Class myframe extends JFrame{public myframe(){public myframe(){

// create panel, buttons, …// create panel, buttons, …}}public static void main(){public static void main(){

JFrame f = new myframe();JFrame f = new myframe();}}public void public void paintpaint(Graphics g){(Graphics g){

super.paint(g); //call overriden methodsuper.paint(g); //call overriden method// paint stuff here// paint stuff here

}}}} Override JFrame methods to add functionalityOverride JFrame methods to add functionality

Simplifying: ImplementsSimplifying: Implements

Class myframe extends JFrame Class myframe extends JFrame

implementsimplements ActionListener { ActionListener {

public myframe(){public myframe(){

// create panel, buttons, …// create panel, buttons, …

btn.addActionListener(btn.addActionListener(thisthis););

}}

public void public void actionPerformedactionPerformed(ActionEvent e){(ActionEvent e){

// button pressed, do stuff here// button pressed, do stuff here

}}

}}

Simplifying: Anonymous classesSimplifying: Anonymous classes

Class myframe extends JFrame {Class myframe extends JFrame {

public myframe(){public myframe(){// create panel, buttons, …// create panel, buttons, …btn.addActionListener(btn.addActionListener( newnew ActionListener() { ActionListener() {

public void public void actionPerformedactionPerformed(ActionEvent e)(ActionEvent e){{

// button pressed, do stuff here// button pressed, do stuff here }}

} } ););

}}}}

Defining and instantiating a class on the fly

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Components use various Components use various listenerslisteners

JButton, JMenuItem, JComboBox, JTextField:JButton, JMenuItem, JComboBox, JTextField:• addActionListener(ActionListener)addActionListener(ActionListener)

public void actionPerformed(ActionEvent event)public void actionPerformed(ActionEvent event) JCheckBox, JRadioButton:JCheckBox, JRadioButton:

• addItemListener(ItemListener)addItemListener(ItemListener) public void itemStateChanged(ItemEvent event)public void itemStateChanged(ItemEvent event)

JSliderJSlider• addChangeListener(ChangeListener)addChangeListener(ChangeListener)

public void stateChanged(ChangeEvent event)public void stateChanged(ChangeEvent event) JTextAreaJTextArea

• getDocument().getDocument().addDocumentListener(DocumentListener)addDocumentListener(DocumentListener) public void insertUpdate(DocumentEvent event)public void insertUpdate(DocumentEvent event) public void removeUpdate(DocumentEvent event)public void removeUpdate(DocumentEvent event) public void changedUpdate(DocumentEvent event)public void changedUpdate(DocumentEvent event)

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Components- Getting valuesComponents- Getting values Some user actions normally cause the program to Some user actions normally cause the program to

dodo something: clicking a button, or selecting from something: clicking a button, or selecting from a menua menu

Some user actions set values to be used Some user actions set values to be used later: later: entering text, setting a checkbox or a radio buttonentering text, setting a checkbox or a radio button• You You cancan listen for events from these, but it’s not listen for events from these, but it’s not

usually a good ideausually a good idea• Instead, Instead, readread their values when you need them their values when you need them

String myText = myJTextField.getText();String myText = myJTextField.getText(); String myText = myJTextArea.getText();String myText = myJTextArea.getText(); boolean checked = myJCheckBox.isSelected();boolean checked = myJCheckBox.isSelected(); boolean selected1 = myJRadioButton1.isSelected();boolean selected1 = myJRadioButton1.isSelected();

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Components - Enabling and disablingComponents - Enabling and disabling It is poor style to remove components It is poor style to remove components

you don’t want the user to be able to you don’t want the user to be able to use use • ““Where did it go? It was here a minute ago!”Where did it go? It was here a minute ago!”• Exception – changing to new interfaceException – changing to new interface

It’s better to It’s better to enableenable and and disabledisable controls controls• Disabled controls appear “grayed out”Disabled controls appear “grayed out”• The user may still wonder The user may still wonder why?why?, but that’s still less confusing, but that’s still less confusing

anyComponentanyComponent.setEnabled(.setEnabled(enabledenabled););• Parameter should beParameter should be true true to enable,to enable, false false to disableto disable

An exampleAn example

Example 1 – a program with 3 buttons and 2 text fields

Step1 – Design the interface

Read Write

Enter text

Correct Entry?

Program

The Program will consist of 2 JPanels –

The top one containing labels and text fields

The bottom one containing three JButtonsThe browser will add a title bar when the applet is running

Swing

Read Write Clear

Enter text

Correct Entry?

Program

The top Panel will use a GridLayout with 2 rows and 2 columns

(with a separation of 10 pixels)

Swing Example 1

//(global) attributes of the classprivate MyJTextField source = new MyJTextField(25);

private MyJTextField target = new MyJTextField(25);

private JLabel edit = new JLabel("Enter text");

private JLabel verify = new JLabel("Correct Entry?");

private String inStr = new String("");

//method to construct the top panel

private JPanel makeJTextPanel( ) {

JPanel theText = new JPanel( );

theText.setLayout(new GridLayout(2,2, 10, 10));

theText.add(edit);

theText.add(source);

theText.add(verify);

theText.add(target);

return theText;

}

Construct the top panel – write a method makeJTextPanel( )

Add components to the grid – left to right, top to bottom

Swing Example 1

Read Write Clear

Enter text

Correct Entry?

Program

Construct the bottom Panel – Use FlowLayout (center adjusted)

Top JPanel

Bottom JPanel

Swing Example 1Construct the bottom panel – with a methodprivate MyJButton read;

private MyJButton write;

private MyJButton clear;

//build the bottom panel with method makeJButtonPanel( )

private JPanel makeJButtonPanel() {

read = new MyJButton ("Read", source);

write = new MyJButton("Write", target);

clear = new MyJButton("Clear", target);

JPanel theButtons = new JPanel( );

theButtons.setLayout(new FlowLayout(FlowLayout.CENTER));

theButtons.add(read);

theButtons.add(write);

theButtons.add(clear);

theButtons.setBackground(Color.blue);

return theButtons;

}

Create the bottom panel

Set its layout and color, and add the buttons to it (left to right)

Swing Example 1Suppose our program is an Applet Place the panels into the applet in method init( )

public void init( ) {

Container cp = getContentPane( );

theButtons = makeJButtonPanel( );

cp.add(BorderLayout.SOUTH, theButtons);

theText = makeJTextPanel( );

cp.add(BorderLayout.CENTER, theText);

}

For heavyweight component like JApplet components must be added to a ContentPane

//add theButtons (a JPanel) to the ContentPane

//the default LayoutManager of a JApplet is BorderLayout

MyJButton objects interact with MyJTextField objects

Swing Example 1Design of the System

A button event will cause a read, write, or clear of a text field.

JPanel

JApplet

MyJTextField

MyJTextField(int size)

doButtonAct(MyJButton)

String response

MyJButtonJLabel

MyJButton(String, MyJTextField)

actionPerformed(ActionEvent)

MyJTextField target

ActionListener

activates

The applet is an aggregate of 2 JPanels2

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describes

JPanels contain JLabels and MyJTextField objects OR MyJButtons

Swing Example 1

class MyJButton extends JButton implements ActionListener {

private MyJTextField target;

public MyJButton(String name, MyJTextField targ) {

Font buttonFont = new Font ("Times Roman", Font.BOLD, 12);

setFont(buttonFont);

setText(name);

setBackground(Color.cyan);

target = targ;

addActionListener(this);

}

public void actionPerformed(ActionEvent e) {

target.doButtonAct(this);

}

}

class MyJButton

Constructor receives handle to text field

Hold handle to target text field

Event causes message to be sent to the target to perform a read or write

Swing Example 1

class MyJTextField extends JTextField {

private String response = new String( );

public MyJTextField(int size) {

super(size);

}

public void doButtonAct(MyJButton source) {

response = source.getText( );

if (response.equals("Read") )

inStr = super.getText( );

else if (response.equals("Write") )

setText(inStr);

else if (response.equals("Clear") )

setText("");

}

}

A MyJButton object notifies a MyJTextField of a button event and elicits an action

Now some more Classes Now some more Classes

Lets examine a few classes in more Lets examine a few classes in more detailsdetails

Swing And JScrollPaneAdding scroll bars to a component such as a JTextArea

Just wrap a JTextArea object inside a JScrollPane.

JTextArea ta = new JTextArea(10, 25);

JScrollPane sp = new JScrollPane(ta);

The programmer can control which scrollbars are allowed – vertical, horizontal, both, or neither

JScrollPane sp = new JScrollPane(ta,

JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,

JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);

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DialogsDialogs A A dialogdialog (small accessory window) (small accessory window)

can be can be modalmodal or or nonmodalnonmodal• When your code opens a modal dialog, it waits for a When your code opens a modal dialog, it waits for a

result from the dialog before continuingresult from the dialog before continuing• When your code opens a nonmodal dialog, it does so in When your code opens a nonmodal dialog, it does so in

a separate thread, and your code just keeps goinga separate thread, and your code just keeps going

Sun supplies a few simple (but Sun supplies a few simple (but useful) useful) modalmodal dialogs for your use dialogs for your use

You can create your own dialogs You can create your own dialogs (with (with JDialogJDialog), but they are ), but they are nonmodalnonmodal by defaultby default

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Message dialogsMessage dialogs JOptionPane.showMessageDialog(parentJFrame,JOptionPane.showMessageDialog(parentJFrame,

"This is a JOptionPane \"message\" "This is a JOptionPane \"message\" dialog.");dialog.");

Notice that Notice that showMessageDialogshowMessageDialog is a is a static method of static method of JOptionPaneJOptionPane

The “The “parentJFrameparentJFrame” is typically your ” is typically your main GUI window (but it’s OK to use main GUI window (but it’s OK to use nullnull if you don’t have a main GUI window)if you don’t have a main GUI window)

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Confirm dialogsConfirm dialogs

int yesNo =int yesNo = JOptionPane.showConfirmDialog(parentJFrame,JOptionPane.showConfirmDialog(parentJFrame, "Is this what you wanted to "Is this what you wanted to see?");see?");

if (yesNo == JOptionPane.YES_OPTION) { ... }if (yesNo == JOptionPane.YES_OPTION) { ... }

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Input dialogsInput dialogs

String userName =String userName = JOptionPane.showInputDialog(parentJFrame, JOptionPane.showInputDialog(parentJFrame, "What is your "What is your name?")name?")

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Option dialogsOption dialogs Object[] options =Object[] options =

new String[] {"English", "Chinese", "French", "German" }; new String[] {"English", "Chinese", "French", "German" };int option =int option = JOptionPane.showOptionDialog(parentJFrame, JOptionPane.showOptionDialog(parentJFrame, "Choose an option:", "Choose an option:", "Option Dialog", "Option Dialog", JOptionPane.YES_NO_OPTION,JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE,JOptionPane.QUESTION_MESSAGE, null, null, options, options, options[0]); options[0]); // use as default// use as default

Fourth argument could be Fourth argument could be JOptionPane.YES_NO_CANCEL_OPTIONJOptionPane.YES_NO_CANCEL_OPTION Fifth argument specifies which icon to use in the dialog; it could be Fifth argument specifies which icon to use in the dialog; it could be

one of one of ERROR_MESSAGEERROR_MESSAGE, , INFORMATION_MESSAGEINFORMATION_MESSAGE, , WARNING_MESSAGEWARNING_MESSAGE, or , or PLAIN_MESSAGEPLAIN_MESSAGE

Sixth argument (Sixth argument (nullnull above) can specify a custom icon above) can specify a custom icon

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Load file dialogsLoad file dialogs JFileChooser chooser = new JFileChooser();JFileChooser chooser = new JFileChooser();

chooser.setDialogTitle("Load which file?");chooser.setDialogTitle("Load which file?"); int result = chooser.showOpenDialog(enclosingJFrame);int result = chooser.showOpenDialog(enclosingJFrame);

if (result == JFileChooser.APPROVE_OPTION) {if (result == JFileChooser.APPROVE_OPTION) { File file = chooser.getSelectedFile(); File file = chooser.getSelectedFile(); // use file // use file}}

You could also test You could also test for for CANCEL_OPTIONCANCEL_OPTION oror ERROR_OPTIONERROR_OPTION

You will get back a You will get back a FileFile object; to use it, object; to use it, you must know how you must know how to do file I/Oto do file I/O

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Save file dialogsSave file dialogs JFileChooser chooser = new JFileChooser();JFileChooser chooser = new JFileChooser();

chooser.setDialogTitle(“Save file as?");chooser.setDialogTitle(“Save file as?"); int result = chooser.showSaveDialog(enclosingJFrame);int result = chooser.showSaveDialog(enclosingJFrame);

if (result == JFileChooser.APPROVE_OPTION) {if (result == JFileChooser.APPROVE_OPTION) { File file = chooser.getSelectedFile(); File file = chooser.getSelectedFile(); // use file // use file}}

You could also test You could also test for for CANCEL_OPTIONCANCEL_OPTION oror ERROR_OPTIONERROR_OPTION

You will get back a You will get back a FileFile object; to use it, object; to use it, you must know how you must know how to do file I/Oto do file I/O