CSC 308 2.0

System Development with Java

Budditha Hettige

Department of Statistics and Computer Science

Introduction to JAVA GUI Programming

Graphical User Interface

• Many Java application use a graphical user interface or GUI

• A GUI is a graphical window or windows that provide interaction with the user.

• GUI‟s accept input from:

– the keyboard

– a mouse.

• A window in a GUI consists of components that:

– present data to the user

– allow interaction with the application.

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Introduction

• Some common GUI components are:

– buttons, labels, text fields, check boxes, radio buttons, combo boxes, and sliders.

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GUI Programming

• GUI programs are event-driven

• Basic types of GUI Programs

– Stand-alone applications

– Applets

• Stranded GUI library

– AWT

– SWINIG

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Abstract Windowing Toolkit(AWT)

• IS a Original Java GUI API

• Very limited in capability

– Few components

– API not well structured, particularly event

handling for user actions

– Not entirely portable (used native widgets)

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JFC/Swing

• Java Foundation Classes (or “Swing”)

– Replacement for AWT (although does share some classes)

– Also provide basis for developing new GUI features (which are being continually added)

• What does Swing include?

– 100% Java

– Swing components (more, and more sophisticated)

– Pluggable Look and Feel Support

– Accessibility API

– Better graphics support (Java 2D)

– Drag and Drop

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JFC/Swing cont…

• Disadvantages

– Can be slow (resource hungry)

– Large complex API (big learning curve)

– Many features best suited for GUI builders, IDEs

• Important to use Swing and not AWT

– Swing is the recommended way to build Java GUIs

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Design Stages of the GUI

1. Design the user interface

– Organising pre-built GUI components to build windows, dialogs

– E.g buttons, tables, menus, etc

2. Writing the application logic

– What does the application do?

3. Writing event-handling code to tie the GUI components to the application logic

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User interface

• A GUI is built in layers.

• Bottom most layer is the window (Container) – Contains all other components

– Can provide basic features like maximise/minimise buttons, title bar, menu bar, etc

• On top of this are layered (Component) – Components, e.g. buttons, text fields

– or intermediate containers, e.g. panels

• Arrangement of components in a contained is handled by a layout manager – Its job is to instruct components on how to arrange

themselves so the GUI is drawn correctly.

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The containment hierarchy

• This layered GUI can be viewed as a hierarchy

of components

– NOT an inheritance hierarchy,

– It just describes how components are nested one

within another

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GUI Application

Jframe

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The containment hierarchy

JFrame

JButton JButton JPanel

JLabel JTextField

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Swing Top level containers

• JWindow

– Basic no frills window, just a square on the screen

• JFrame

– The basic Swing window. Offers basic window controls, resizable

• JDialog

– For building dialog boxes, e.g. File open/save

• JApplet

– For building applets, embedded into a web page

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New containers (Netbeans)

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SWING containers

• Panel

• Scroll Pane

• Tool Bar etc

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Working with JFrames

• Many different possibilities, but the basics

include:

– Setting window title

– Setting location on screen

– Setting size of window

– Restricting resizes

– Set close operation (exit the program), as by

default it does nothing.

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Example

public class NewJFrame extends javax.swing.JFrame {

public NewJFrame() {

initComponents();

}

public static void main(String args[]) {

java.awt.EventQueue.invokeLater(new Runnable() {

public void run() {

new NewJFrame().setVisible(true);

}

});

}

}

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Example

private void initComponents() {

setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

setTitle("Test Window");

setAlwaysOnTop(true);

javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());

getContentPane().setLayout(layout);

layout.setHorizontalGroup(

layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)

.addGap(0, 251, Short.MAX_VALUE)

);

layout.setVerticalGroup(

layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)

.addGap(0, 189, Short.MAX_VALUE)

);

}

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close operation

Set size of the window

Set title of the window

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Adding Components to a Frame

• A JFrame has several areas

– Window decorations

– (Optional) Menu bar

– Content pane

• Content pane is where components are added.

– Content pane is a Container object

– Obtain reference to the content pane, and then add another component to it

JFrame frame = new JFrame(“Example”);

JButton button = new JButton(“Click me!”);

frame.getContentPane().add( button );

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Adding Components

• Very common to extend the Swing components,

particularly JFrame

– Create your own specialised versions

– May include a fixed set of components

– Provide extra methods for working with those components,

etc.

– Encapsulates how the GUI is constructed

• Slightly different to Visual Basic where one tends to

just use the basic components

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Layout Managers

• Responsible for layout out (arranging)

components in a Container

• Several different types with different uses

• None of them provide for precise x-y

alignment, unlike VB forms

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Border Layout

• This is the default layout for JFrame

• Divides the content pane into 5 areas (north, south, east, west, center)

• Areas are expanded/contracted as needed, along with their contents. – Therefore ignores preferred size of the components.

• Center is the default if not specified.

• Adding two components to the same zone means they get added one on top of the other – Instead add the components to a JPanel, and then add that

instead.

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Border Layout

X

NORTH

SOUTH

CENTER WEST EAST

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Grid Layout

• Divides the container into a rectangular grid

– Configurable number rows/columns

• Each grid location is of equal size, one

component assigned to each.

• Automatically assigns components to next

available location

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Other layout managers

• Flow Layout (default for JPanel)

– Arranges components left-to-right

– Used to arrange buttons on a panel

• Card Layout

– Arranges components like a deck of cards

– Only one card visible at a time

• Box Layout, Grid Bag Layout

– Very sophisticated managers, used by GUI builders for very precise GUI designs.

– Not recommended for hand use!

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Menus

• A Jframe can have only a single menu bar

– Instance of the Jmenu object

• A menu bar can have several menus on it

– Instances of the Jmenu object

• A menu can have several items on it

– Instances of the JmenuItem object

• Example

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Controls

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Swing Controls - Label

• Use to display text

• Codes private javax.swing.JLabel jLabel1;

jLabel1 = new javax.swing.JLabel(); // create object

jLabel1.setFont(new java.awt.Font("Tahoma", 0, 12)); // Set fonts jLabel1.setText("jLabel1"); // Set lables

// place the control in to the pane

layout.setVerticalGroup( .....

.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)

layout.setHorizontalGroup( .....

.addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 25, javax.swing.GroupLayout.PREFERRED_SIZE)

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Text field

• Use to input/output a text

• Sample Codes private javax.swing.JTextField jTextField1;

jTextField1 = new javax.swing.JTextField();

jTextField1.setText("jTextField1");

layout.setVerticalGroup( .....

.addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, 190, javax.swing.GroupLayout.PREFERRED_SIZE)

layout.setHorizontalGroup( .....

.addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))

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Text field data access

• Set text

jTextField1.setText(“text");

• Get text form the text field

String data;

data = jTextField1.getText();

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Buttons

• Place the button

• Rename the button

• Add action event

• Modify the function private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {

// TODO add your handling code here:

}

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Combo box

• Select a item from a list

• Codes

private javax.swing.JComboBox jComboBox1;

jComboBox1 = new javax.swing.JComboBox();

jComboBox1.setModel(new

javax.swing.DefaultComboBoxModel(new String[]

{ "Item 1", "Item 2", "Item 3", "Item 4" }));

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Data Access

• Get selected item from the combo box

String ss;

ss = (String)jComboBox1.getSelectedItem();

Type casting

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Event Handling

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Handling Basics

• Swing Events Examples

– Actions

– Mouse Events

– Window Events

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Event Handling Conventions

• Event object typically extend java.awt.Event

– Some of the „newer‟ ones don‟t

• Events share some common attributes

– a timestamp, source object, etc

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Action Events

• Very tedious implementation if all activities were dealt with as individual clicks

• Swing provides higher level „action‟ event

• Meaning of event depends on component

– E.g. button click, menu selection, etc

• Basic classes: – ActionEvent – identifies action, key modifiers, etc

– ActionListener – single actionPerformed method

– addActionListener, removeActionListener methods on Component

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Code

Use

Action Listener java.awt.event.ActionListener

Action Event java.awt.event.ActionEvent

Code

jButton1.addActionListener(new java.awt.event.ActionListener() {

public void actionPerformed(java.awt.event.ActionEvent evt) {

jButton1ActionPerformed(evt);

}

});

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {

// TODO add your handling code here:

}

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Event Handling Conventions

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Mouse Events

• Natural for Swing to expose mouse-related events

– It‟s how the user interacts with the GUI

• MouseListener interface describes the basic

events

• Each method accepts a MouseEvent object

parameter

• java.awt.Component has add/remove listener

methods

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Mouse Events

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Mouse Events

• So, capturing basic mouse events involves:

– Creating an implementation of MouseListener

– Calling addMouseListener on one or more

Components to register it

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Window Events

• Swing allows the capturing of window related events

– Activate, deactivate, minimise, open, close etc

• setDefaultCloseOperation is only useful if you don‟t want to do anything complex

• Basic classes/methods

– WindowEvent – identifies Window

– WindowListener – range of methods

– addWindowListener, removeWindowListener methods on JFrame, JWindow, JDialog

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Other Swing Events

• More Mouse events – Mouse motion, mouse wheels

• Item events – Selecting/deselecting items in lists, checkboxes, etc

• Key Events – Raw keyboard input

• Tree Events – Opening/closing nodes in a tree component

• Drag and drop

• …and many more. See javax.swing.event and java.awt.event packages.

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Mouse events

Use

Mouse Event java.awt.event.MouseEvent

Mouse Listener java.awt.event.MouseAdapter

Code

jButton2.addMouseListener(new java.awt.event.MouseAdapter() {

public void mouseEntered(java.awt.event.MouseEvent evt) {

jButton2MouseEntered(evt);

}

});

private void jButton2MouseEntered(java.awt.event.MouseEvent evt) {

// TODO add your handling code here:

}

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Key events

Use

java.awt.event.KeyEvent

Code

jButton2.addKeyListener(new java.awt.event.KeyAdapter() {

public void keyPressed(java.awt.event.KeyEvent evt) {

jButton2KeyPressed(evt);

}

});

private void jButton2KeyPressed(java.awt.event.KeyEvent evt) {

// TODO add your handling code here:

}

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Dialog Boxes

• A dialog box is a small graphical window that displays a message to the user or requests input.

• A variety of dialog boxes can be displayed using the JOptionPane class. – Message Dialog - a dialog box that displays a

message.

– Input Dialog - a dialog box that prompts the user for input.

– Confirm Dialog This is a dialog box that asks the user a Yes/No question.

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Dialog Boxes

The JOptionPane class provides static

methods to display each type of dialog box.

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Message Dialogs

• JOptionPane.showMessageDialog method is used to display a message dialog.

• There are several overloaded versions of this method. showMessageDialog(Component parent,

Object message)

showMessageDialog(Component parent,

Object message,

String title,

int messageType)

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Message Dialogs

JOptionPane.showMessageDialog(null, "Hello World");

• The first argument can be a reference to a graphical

component.

– The dialog box is displayed inside that component.

– If null is passed as the first argument, which causes the dialog

box to be displayed in the center of the screen.

• The second argument is the message that is to be

displayed.

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Message Dialogs

• By default the dialog box has:

– the string “Message” displayed in its title bar, and

– an information icon (showing the letter “i) is displayed. JOptionPane.showMessageDialog(null,

"Invalid Data",

"My Message Box",

JOptionPane.ERROR_MESSAGE);

• The third option is the title bar text.

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Message Dialogs

• These constants can be use to control the icon

that is displayed.

– JOptionPane.ERROR_MESSAGE

– JOptionPane.INFORMATION_MESSAGE

– JOptionPane.WARNING_MESSAGE

– JOptionPane.QUESTION_MESSAGE

– JOptionPane.PLAIN_MESSAGE

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Message Dialogs

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Input Dialogs

• An input dialog is a quick and simple way to

ask the user to enter data.

• The dialog displays a text field, an Ok button

and a Cancel button.

• If Ok is pressed, the dialog returns the user‟s

input.

• If Cancel is pressed, the dialog returns null.

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Input Dialogs

• The JOptionPane has several overloaded versions of the static showInputDialog method.

• Here are two of them: showInputDialog(Object message)

showInputDialog(Component parent,

Object message,

String title,

int messageType)

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Input Dialogs

String name;

name = JOptionPane.showInputDialog("Enter your

name.");

• The argument passed to the method is the message to display.

• If the user clicks on the OK button, name references the string entered by the user.

• If the user clicks on the Cancel button, name references null.

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Input Dialogs

• By default the input dialog box: – has the string “Input” in its title bar, and

– displays a question icon. String value;

value = JOptionPane.showInputDialog(null,

"Enter the value again.",

"Enter Carefully!",

JOptionPane.WARNING_MESSAGE);

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Confirm Dialog

• A confirm dialog box typically asks the user a yes or no

question.

• By default Yes, No, and Cancel buttons are displayed.

• The showConfirmDialog method is used to

display a confirm dialog box.

• There are several overloaded versions of this method. int showConfirmDialog(Component parent,

Object message)

int showConfirmDialog(Component parent,

Object message,

String title,

int optionType)

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Confirm Dialog

int value;

value = JOptionPane.showConfirmDialog(null, "Are you sure?");

• By default the confirm dialog box displays: – “Select an Option” in its title bar,

– Yes, No, and Cancel buttons.

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Confirm Dialog

• The showConfirmDialog method returns

an integer that represents the button clicked

by the user.

• The button that was clicked is determined by

comparing the method‟s return value to one of

the following constants:

– JOptionPane.YES_OPTION

– JOptionPane.NO_OPTION

– JOptionPane.CANCEL_OPTION

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Confirm Dialog

int value;

value = JOptionPane.showConfirmDialog(null,

"Are you sure?");

if (value == JOptionPane.YES_OPTION){

//If the user clicked Yes, this code is executed.

}

else if (value == JOptionPane.NO_OPTION){

//If the user clicked no, this code is executed.

}

else if (value == JOptionPane.CANCEL_OPTION){

//If the user clicked Cancel, this code is executed.

}

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Confirm Dialog

int value;

value = JOptionPane.showConfirmDialog(null,

"Are you sure?",

"Please Confirm", JOptionPane.YES_NO_OPTION);

• One of the following constants can be used for the fourth parameter: – JOptionPane.YES_NO_OPTION

– JOptionPane.YES_NO_CANCEL_OPTION

Example:

TestAverageDialog.java

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Example - Calculator

Create a calculator application to calculate the

numbers and print the result

Supported Operators

+ - / * ^ and squrt

Supported action C , < (Back)

Display – total with number of numbers

used for calculation

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