JAVA Lecture Slides

8/11/2019 JAVA Lecture Slides

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ICT 314 ADVANCED JAVA TECHNOLOGY

Instructor: r d appiah



R D Appiah

Introduction: Building User Interfaces

In the earlier versions of Java, the building of graphical

user interfaces is usually achieved through the use of

a set of classes called the Abstract Windowing Toolkit

(AWT)

In this course, we will learn the use of the javax.swingpackage to create and design user interfaces.

This will be followed by the skills to arrange all of the

components on a user interface

And finally, learning to make user interface(s)

responsive to user control(s).



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The Abstract Windowing Toolkit

This is a set of classes that enables you to

create a graphical user interface and receiveuser input from the mouse and keyboard.

Because Java is a platform-independent

language, the AWT offers a way to design aninterface that will have the same general

appearance and functionality on all systems it

runs on.

However, it is always advised that developers

must test their AWT-based interfaces on as

many platforms and browsers as possible.



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The components of a GUI:

An interface created based on GUI may consist

of three basic things:Components: Anything that can be put onto a

user interface, including clickable buttons,

scrolling lists, pop-up menus, check boxes, andtext fields.

Containers: A component that can contain

other components. These may include suchthings as an Applet window, Panels, Dialog

boxes, and other standalone windows.



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Layout Managers: These are objects that

define how the components in a container will

be arranged. Normally, one does not see alayout manager in an interface, but rather the

results of its action(s).

The AWT’s classes are all available within the java.awt.* package.

Thus, to make all of its resources available in a

programme, one has to add the following importstatement at the top of the source codes:

import java.awt.*;



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The user-interface Components:

Components are placed onto a user interface

by adding them to a container.

Note also that a container is itself a component

and can be added to other containers – thus acontainer within a container.

To a higher extent, we will use both the

java.awt.* and javax.swing.* packages to designuser interfaces.



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Steps:

A component is added to a container via the

following two steps:• Create the component of interest and

• Call the container’s add( ) method with the

component.



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GUI I/O WITH JOptionPane

The JOptionPane class is used to provide

simple GUI-based input and output interfaces.It is important to note that the JOptionPane

class support only a string input.

Thus, to input a numerical value, we need to

perform the string conversion ourselves.

To achieve this, Java provides a feature calledwrapper classes and their corresponding

conversion methods, as follows:



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Common wrapper classes and their

conversion methods:

Class Method Example

Integer parseInt Integer.parseInt(“45”)

-> 45

Long parseLong Long.parseLong(“45”)

-> 45L

Float parseFloat Float.parseFloat(“45.8”)

-> 45.8F

Double parseDouble Double.parseDouble(“45”

) -> 45.0



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Customizing Frame Windows

Creating a customized user interface involves

defining a subclass of the JFrame class.The JFrame class contains the most

rudimentary functionalities to support features

found in any frame window, such asminimizing, moving and resizing the window.

For practical programming reasons, we

normally define a subclass of the JFrame classand add methods and data members to

implement the needed functionalities.



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Illustration:

Refer to Ex6DefaultJFrame.java

To define a subclass of another class, wedeclare the subclass with the reserved word

extends.

To illustrate this, refer to Ex7JFrameSubclass.java

Notice that we declared the variable

contentPane in the changeBackColor() methodas a Container. We do not have a class called

ContentPane.



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Button Placement

Refer to Ex9JButtonFrame.java

The type of button we use here is called apushbutton.

To use a button in a programme, we create an

instance of the javax.swing.JButton class.

We declare and create these buttons in the

following manner:

import javax.swing.*;

…JButton cancelButton, okButton;

cancelButton = new JButton(“CANCEL”);

okButton = new JButton(“OK”);



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Setting The Layout

In Ex9JButtonFrame.java, we use the simplest

layout manager called FlowLayout.Here, we use the FlowLayout manager - which

places GUI objects in a top-to-buttom, left-to-

right order.Placing GUI objects on the content pane by

explicitly specifying their position and size is

known as absolute positioning.

We will discuss other common layout managers

and absolute positioning in later parts of the

course.



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Handling Events

An action, such as clicking a button is called an

event; and the mechanism to process theevents is called event handling.

The event-handling model of Java is based on

the concept known as the delegation based

event model.

With this model, event handling involves two

types of Objects:• event source objects and

• event listener objects.



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A GUI object, such as a button, where the event

occurs is called the event source – and we say

an event source generates events.

When an event is generated, the system

notifies the relevant event listener object or

simply an event listener.

An event listener is an object that includes a

method that gets executed in response to

generated events.In Java, it is possible for a single object to be

both an event source and an event listener.



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One of the most commonly used events in Java

is called an action event.

For example, when a button is clicked or amenu item is selected, an event source will

generate an action event.

For the generated events to be processed, wemust associate, or register , event listeners to

the event sources.

If the event sources have no registeredlisteners, then generated events are simply

ignored.



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An object that can be registered as an action

listener must be an instance of a class that is

declared specifically for the purpose.

Such classes are called action listener

classes.

Thus, an object created from an action listener

class becomes an action listener object.

An action listener is associated to an action

event source by calling the source’s

addActionListener() method.This is done by passing the action listener as

an argument in the process.



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Example:

To register an instance of ButtonHandler as an

action listener of okButton and cancelButton,we execute the following code:

ButtonHandler handler = new ButtonHanler( );

okButton.addActionListener(handler);cancelButton.addActionListener(handler);

Note that we are associating a single listener tomultiple event sources; and multiple listeners

can also be associated to a single event source.



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As an example, refer to

Ex11ButtonFrameHandler.java

An Interface: An interface is a collection of methods that

indicate a class has some behaviour in addition

to what it inherits from its superclasses.They are said to be templates of behaviour that

other classes are expected to implement.

Interfaces serve as reference data types – these include constants and abstract

methods.



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An abstract method has only the method

header ( or more formally, the method

prototype) – that is a method that has no body.

Trial Questions – Quick Checks:

1. What is the purpose of a layout manager?

2. Which object generates events? Which objectprocesses events?

3. What method must be implemented by a class that

implements the ActionListener interface?

4. What does the getActionCommand method of the ActionEvent class return?

5. What are interfaces used for in Java

programming?



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Text-Related GUI Components

JLabel, JTextField and JTextArea

JLabel and JTextField deal with a single line of textwhile the JTextArea deals with multiple lines of text.

JTextField

Like a JButton object, an instance ofJTextField generates an action event when the

user presses the Enter key while the object is

active.We handle the JTextField object and register

its action listener much the same way as we

did for the JButton class.



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Thus, in the declaration part, we add:

JTextField myTextField;

And in the constructor we create a JTextFieldobject and register the frame as its action

listener, as follows:

public Ex12TextFrame ( ){…

myTextField = new JTextField();

myTextField.setColums(22);

add(myTextField);myTextField.addActionListener(this);

…



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After this stage, we are ready to modify the

actionPerformed method to handle both the

Button click events and the Enter key events.

In this case we have three event sources (two

buttons and one text field), and so we first

have to determine the source within the

actionPerformed method.

We use the instanceof operator to determine

the class to which the event source belongs.

We will also use the getText( ) method of the

JTextField class to retrieve the text that the

user has entered.



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The complete method looks like:

public void actionPerformed(ActionEvent event) {

if(event.getSource( ) instanceof JButton) {

JButton clickedButton = (JButton) event.getSource( );

String buttonText = clickedButton.getText( );

setTitle(“You Clicke ” + buttonText);

} else { // the event source is inputLinesetTitle(“You Entered ‘ ” + inputLine.getText( ) + “ ’ ”);

}

}



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Adding a JLabel Object:

A JLabel object is useful in displaying a label

that explains the purpose of the text field.

We will modify the Ex12TextFrame class by

placing a JLabel “PLEASE ENTER YOUR

NAME” above the text field.

Thus, we will add a data member declaration:

private JLabel prompt;We then create the object in the constructor as:



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public Ex13TextFrame {

…

prompt = new JLabel ( );

prompt.setText(“PLEASE ENTER YOU NAME”);prompt.setSize(150, 25);

contentPane.add(prompt);

…

}

We can also set the text at the time of objectcreation as:

prompt = new JLabel (“PLEASE ENTER YOUR

NAME”);

Refer to Ex13TextFrame.java for an example.



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The ImageIcon Object

We can also use the JLabel class to display

images.

To display an image, we pass an ImageIcon

object when we create a JLabel object instead

of a string.

To create this ImageIcon object, we must

specify the filename of an image.

We can add the data member declaration and

add an image jack.jpg, as follows:



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private JLabel image;

public Ex14TextFrame {

…image = new JLabel (new ImageIcon (“jack.jpg” ) );

image.setSize(50,50);

contentPane.add(image);

…

}

For an example, refer to Ex14TextFrame.java



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The JTextArea Object

Here, we declare a JTextArea object in the data

member section of the programmeEx15TextArea.java, as follows:

private JTextArea textArea;

textArea = new JTextArea( );textArea.setColumns(22);

textArea.setRows(8);

textArea.setBorder(

BorderFactory.createLineBorder(Color.RED) );textArea.setEditable(false);

contentPane.add(textArea);

Using The JScrollPane To Add Scroll Bars



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Using The JScrollPane To Add Scroll Bars

Automatically.

Adding scroll bars that will appear automatically

when needed, we replace the statement:

contentPane.add(textArea);

of Ex15TextArea.java with the following codes:

JScollPane scrollText = new JScrollPane(textArea);

scrollText.setSize(200, 140);contentPane.add(scrollText);

For the complete programme, refer to

Ex15TextAreaScroll.java

LAYOUT MANAGERS



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LAYOUT MANAGERS

The three major layout managers in use are

The java.awt.FlowLayout Manager. The java.awt.BorderLayout Manager.

The java.awt.GridLayout Manager.

The java.awt.BorderLayout Manager

This layout manager divides the container into

five regions:Center; North; South; East; and

West.

E l



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Example:

The following set the contentPane’s layout and

then add five buttons to the container:contentPane.setLayout(new BorderLayout(20, 10 ) );

contentPane.add(button1, BorderLayout.NORTH);contentPane.add(button2, BorderLayout.SOUTH);

contentPane.add(button3, BorderLayout.EAST);

contentPane.add(button4, BorderLayout.WEST);

contentPane.add(button5, BorderLayout.CENTER);Refer to Ex16BorderLayout.java for an

illustrative example.

Th j t G idL t M



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The java.awt.GridLayout Manager:

This places GUI components on equal-size N X

M grids.Before using the grid layout, one needs to

create a GridLayout object.

To create a GridLayout object, we pass twoarguments, representing the number of rows,

and the number of columns. For example:

contentPane.setLayout(new GridLayout(2, 3));

Note that, here components are placed in top-

to-bottom, left-to-right order.

R f t E 17G idL t j f l



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Refer to Ex17GridLayout.java for an example.

Absolute Positioning

It is also possible not to use any layoutmanager – in which case we must explicitly

specify the position and size of the component

to be placed on the container.

We refer to the above approach as absolute

positioning.

You must note that to build attractive and

practical GUI-based Java programmers, one

must learn how to use layout managers

effectively.

T b l t iti i t th l t



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To use absolute positioning, we set the layout

manager of a frame’s content pane to none by

passing null to the setLayout method, as

shown bolow:

contentPane.setLayout ( null ) ;

After this, and in the case of a button, we callthe setBounds method from the JButton class to

help us place the button at the desired location

and also to set the button to the desired size, asfollows:

clearButton.setBounds (75, 130, 80, 35) ;

R f t E 18Ab l t P j f



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Refer to Ex18AbsolutePos.java for an

example.

Effective Use of Nested PanelsFor practical programming purposes, it is

common to see a combination of different layout

managers in the same programme.

Refer to Ex19NestedPanels.java and

Ex20NestedPanels.java for examples on

nested panels.

JCheckBo and JRadioB tton



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JCheckBox and JRadioButton

Compared with the JButton class which

represents a type of button called a

pushbutton, the other two common types of

buttons are called check-boxes and radio

buttons.

For illustrative examples of check-boxes, refer

to Ex19JCheckBox1.java, Ex19CheckBox2.

For illustrative examples of radio buttons, refer

to Ex20JRadioButton.java.



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JCheckBox and JRadioButton Classes

Compared with the JButton class which

represents a type of button called a

pushbutton, the other two common types of

buttons are called check-boxes and radio

buttons.

For illustrative examples of check-boxes, refer

to Ex19JCheckBox1.java, Ex19CheckBox2.

For illustrative examples of radio buttons, refer

to Ex20JRadioButton.java.

Th JC b B Cl



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The JComboBox Class

The JComboBox class represents a combo box.

This class is similar to the JRadioButton class inthat is also allows the user to select an item

from a list of possible choices.

The basic difference between the two lies inhow the choices are presented to the user. It is

also referred to as Drop Down List.

Refer to Ex21JComboBox.java for anillustrative example.

Th JLi t Cl



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The JList Class

The JList class is useful when we need to

display a list of items like: a list of students;a list of files; and so forth.

A JList object is constructed by passing an

array of String object to the JList constructor.Example:

String names = {“James”, “Adams”, “Joel”,

“Mercy”, ‘Joyce”, “Paul” };JList list = new JList (names);

With JLi t h ti f if i



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With JList we have an option of specifying one

of the three selection modes:

1. Single Selection2. Single Interval

3. Multiple Interval.

The single selection mode allows the user toselect only one item at a time.

The single interval mode allows the user to

select a single contiguous interval.The multiple interval mode allows the user to

select multiple contiguous intervals (each

interval will include one or more items).

N ll th lti l i t l d i th



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Normally, the multiple interval mode is the

default mode. The following three statements

show how to set the three selection modes:

list.setSelectionMode(

ListSelectionModel.SINGLE_SELECTION);


ListSelectionModel.SINGLE_INTERVAL_SELECTION);


ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);

F ill t ti l f t



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For an illustrative example, refer to

Ex22JList.java

Th JSlid Cl



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The JSlider Class

The JSlider class represents a slider in which

the user can move a nob to a desired position,and the position of the nob at any time

determines the selected value.

Sliders are created and initialized in the

following manner:

JSlider slider = new JSlider( );

slider.setOrientation(JSlider.VERTICAL);

slider.setPaintLabels(true); // show tick mark labels

slider.setPaintTicks(true); // show tick marks

slider.setMinimum(MIN_COLOR);

lid tM i (MAX COLOR)



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slider.setMaximum(MAX_COLOR);

slider.setValue(MAX_COLOR); //nob’s initial position

slider.setMajorTickSpacing(50);

slider.setMinorTickSpacing(25);

When a nob is moved, a JSlider object

generates a change event – this event occurs

when there is a change in the event source,

such as when the nob is moved.

To process change events, we must registerchange event listeners to a JSlider event source

object.

The class that implements the ChangeListener



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The class that implements the ChangeListener

interface must define a method called

stateChanged, whose parameter is an instance

of ChangeEvent.

As an example, lets consider a Java

programme that behaves in such a way that

whenever a change event is generated, we

read the value from each slider and set the

background colour of a panel to a designated

colour.The stateChanged method will have the

following body:

int R G B;



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int R, G, B;

R = redSlider.getValue( );

G = greenSlider.getValue( );

B = blueSlider.getValue( );

colorPanel.setBackground(new Color(R,G,B));

The values of R,G,B range between 0 and 255

inclusively.

For the full code listing of the programme, referto Ex23JSliderSample.java

Menus in Java



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Menus in Java

Menus are used to support graphical user

interfaces.

In this section, we will describe how to display

menus and process menu events by using

JMenu, JMenuItem and JMenuBar from the

javax.swing package.

Steps in creating and adding menu items:

1. Create a JMenuBar object and attach it to a

frame.

2. Create a JMenu object.

3 Create JMenuItem objects and add them to



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3. Create JMenuItem objects and add them to

the JMenu object.

4. Attach the JMenu object to the JMenuBar object.

Lets create two JMenu object: fileMenu and

editMenu.

fileMenu = new JMenu(“File”);

We then create and add a menu item “New” tofileMenu, as follows:

item = new JMenuItem(“New”);



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item = new JMenuItem( New );

item.addActionListener(this);

fileMenu.add(item);

We repeat this sequence for all other items.

Note also that menu items are placed from the

top in the other they are added to the menu.

We can also include a horizontal line as a

separator between menu items by calling the

menu’s addSeparator method:

fileMenu.addSeparator( );

After the menus and their menu items are



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After the menus and their menu items are

created, we attach them to a menu bar. We do

this in the constructor, where we create a

JMenuBar object, attach it to the frame by

calling the frame’s setMenuBar method, as

follows:

JMenuBar menuBar = new JMenuBar( );setMenuBar(menuBar); // attach it to the frame

menuBar.add(fileMenu);

menuBar.add(editMenu);We then show how to display which menu item

was selected, by using a JLabel object

response. We add response to the frame by:

response = new JLabel (“Hello This is Your Tester”);



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response = new JLabel (“Hello, This is Your Tester”);

response.setSize(250, 50);

contentPane.add(response);

When a menu item is selected, the registered

action listener’s actionPerformed method is

called. Consider the following:

String menuName;

menuName = event.getActionCommand ( );

if (menuName.equals (“ Quit” ) ) {

System.exit (0);

} else {

response.setText(“ Menu Item ” + menuName + “ is Selected “ );

}

For an illustrative example refer to



For an illustrative example, refer to

Ex24JMenuFrame.java

Handling Mouse EventsIn this section, we will describe the handling of

mouse events. In general, mouse events

include such user interactions as moving themouse, dragging the mouse and clicking the

mouse buttons.

For an illustrative example, refer toEx25TrackMouseFrame.java

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