1. Chapter 13—Understanding Swing Components
ISQS 6337 – Jim Burns

2. Using the JFrame Class
There are lots of other UI components, such as buttons, check boxes, and menus that are included in the JFrame Class
In this chapter you will learn how to add these UI components to applets and applications
Such Swing components as JButton, JLabel are easy to use

3. To use these JFrame UI Components…
You insert the import statement
import javax.swing.*;
at the beginning of your Java program files

4. About Swing components
Most Swing components are said to be lightweight because they do not rely upon methods that are part of the operating system
An exception is the JFrame component because it does require interaction with the local operating system, so it is a heavyweight component

5. More about Swing components…
You usually place them in containers
A container is a type of component that holds other components so you can treat a group of them as a single entity
You usually create a JFrame so that you can place other objects within it for display.

6. JFrame Inheritance Hierarchy
Java.lang.Object
Java.awt.Component
Java.awt.Container
Java.awt.Window
Java.awt.Frame
javax.swing.JFrame

7. JFrame Constructors
JFrame() constructs a new frame that initially is invisible and has no title
JFrame(String title) creates a new, initially invisible JFrame with the specified title
JFrame(GraphicsConfiguration gc) creates a JFrame in the specified GraphicsConfiguration of a screen device with a blank title
JFrame(String title, GraphicsConfiguration gc) creates a JFrame with the specified title and the specified GraphicsConfiguration of a screen

8. Constructing a JFrame
You do this just as you would any other other object instantiated from a conventional class
JFrame firstFrame = new JFrame(“Hello”);
JFrame secondFrame = new JFrame();
After you create a JFrame object, you can use the now-familiar object-dot-method format you have used with other objects to call methods that maniuplate a JFrame’s features

9. Methods in the JFrame class
void setTitle(String)
void setSize(int, int)
void setSize(Dimension)
string getTitle()
void setResizable(boolean)
boolean isResizable()
void setvisible(boolean)
void setBounds(int, int, int, int)

10. Examples of method usage…
firstFrame.setSize(200, 100);
firstFrame.setTitle(“My frame”);

11. The JFrame1 application
import javax.swing.*;
public class JFrame1 {
public static void main(String[] args)
JFrame aFrame = new JFrame("First frame");
aFrame.setSize(200,100);
aFrame.setVisible(true); }

12. The code in the slide above…
Creates a small empy JFrame
This window has all the behaviros of any conventionial window—can change the frame’s size by dragging its border, can reposition the frame by dragging the title bar, can Minimize, Maximize or Restore, and Close with buttons in the title bar of the frame’s upper-right corner and a menu under the icon in the upper-left corner

13. The JFrame2 class import javax.swing.*; import java.awt.*;
public class JFrame2 {
public static void main(String[] args)
final int FRAME_WIDTH = 200;
final int FRAME_HEIGHT = 100;
JFrame aFrame = new JFrame("Second frame");
aFrame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
aFrame.setVisible(true);
aFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel label = new JLabel("Hello");
Container con = aFrame.getContentPane();
con.setLayout(new FlowLayout());
con.add(label); }

14. Customizing a JFrame’s Appearance
Items like an icon in the upper-left title bar and the minimize, maximize and close buttons are known as window decorations
Window decorations are supplied by the operating system
However, you can request that Java’s look and feel provide the decorations

15. A JFrame’s Look and Feel
Optionally, you can set a JFrame’s look and feel using the
setDefaultLookandFeelDecorated() method
Use of this is shown in the next program

16. import javax.swing.*;
import java.awt.*;
public class JFrame3 {
public static void main(String[] args)
final int FRAME_WIDTH = 200;
final int FRAME_HEIGHT = 100;
JFrame.setDefaultLookAndFeelDecorated(true);
JFrame aFrame = new JFrame("Third frame");
aFrame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
aFrame.setVisible(true);
aFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel label = new JLabel("Hello");
Container con = aFrame.getContentPane();
con.setLayout(new FlowLayout());
con.add(label); }

17. Java’s Look and Feel
With the exception of the pink line, this program is identical to the previous one
It generates a JFrame that looks as shown below
This window avoids possible law suits involving copyright infringement of the look and feel of another firm

18. Extending the JFrame Class
You can instantiate a JFrame object in any method you choose, including main() and Init() methods
Alternatively, you can create your own class that descends from a JFrame class
The advantage of creating a child class of a JFrame class is that you set the JFrame’s properties within your object’s constructor method; then, when you create your JFrame child object, it is automatically endowed with the features, such as size, that you have specified

19. Using a child class of the JFrame class…
Enables you to set properties such as the size of the JFrame, whether the JFrame is visible, and its look and feel
You do this all in the constructor of the child class

20. The JMyFrame class import javax.swing.*;
public class JMyFrame extends JFrame {
final int WIDTH = 400;
final int HEIGHT = 120;
public JMyFrame()
super("This is my frame");
setSize(WIDTH, HEIGHT);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); }

21. Look at the JMyFrame class above
The first statement in the constructor is the super(“This is my frame”);
This statement calls the parent class’ constructor and sets the title in the title bar to show This is my frame

22. The CreateTwoJMyFrameObjects App
public class CreateTwoJMyFrameObjects {
public static void main(String[] args)
JMyFrame myFrame = new JMyFrame();
JMyFrame mySecondFrame = new JMyFrame(); }

23. The above code…
Creates two JMyFrame windows, both identical, as each has the same set of attributes

24. Using the JPanel Class The simplest Swing container is the JPanel
It is a plain, borderless surface that can hold lightweight UI components

25. import javax.swing.*;
import java.awt.*;
public class JFrameWithPanels extends JFrame {
final int SIZE = 150;
JButton button1 = new JButton("One");
JButton button2 = new JButton("Two");
JButton button3 = new JButton("Three");
public JFrameWithPanels()
super("JFrame with Panels");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel pane = new JPanel();
JPanel pane2 = new JPanel();
Container con = getContentPane();
con.setLayout(new FlowLayout());
con.add(pane);
con.add(pane2);
pane.add(button1);
pane.setBackground(Color.BLUE);
pane2.add(button2);
pane2.add(button3);
pane2.setBackground(Color.BLUE);
setSize(SIZE, SIZE);
setVisible(true); }

26. JPanel Inheritance Hierarchy
Java.lang.Object
Java.awt.Component
Java.awt.Container
Java.swing.JComponent
Java.awt.JPanel

27. Create JFrame with Panels
public class CreateJFrameWithPanels {
public static void main(String[] args)
JFrameWithPanels panel = new JFrameWithPanels(); }

28. Understanding Swing Event Listeners
Classes that respond to user-initiated events, such as button clicks, must implement an interface that deals with, or handles, the events.
These interfaces are called event listeners.
You first used these in chapter 9 when you used the ActionListener interface with JButton objects.
A class can implement as many listeners as it needs.

29. User-initiated events
An event occurs every time a user clicks a mouse or types a character
Listed below are some event listeners

30. Listener Type of Events Example ActionListener Action events
Button clicks
AdjustmentListener
Adjustment event
Scroll bar moves
ChangeListener
Change events
Slider is repositioned
FocusListener
Keyboard focus events
Text field gains or loses focus
ItemListener
Item events
Check box changes status
KeyListener
Keyboard events
Text is entered
MouseListener
Mouse events
Mouse clicks
MouseMotionListener
Mouse movement events
Mouse rolls
WindowListener
Window events
Window closes

31. Event Listeners
Any object can be notified of an event as long as it implements the appropriate interface and is registered as an event listener on the appropriate event source

32. Components
Associated Listener-Registering Methods
JButton, JCheckBox, JComboBox, JTextField, and JRadioButton
addActionListener()
JScrollBar
addAdjustmentListener()
All Swing components
addFocusListener(), addKeyListener(), addMouseListener(), addMouseMotionListener()
JButton, JCheckbox, JComboBox, & JRadioButton
addItemListener()
All JWindow and JFrame components
Add WindowListener()
JSlider and JCheckbox
addChangeListener()

33. The format for a listener statement is…
theSourceOfTheEvent.addListenerMethod (theClassThatShouldRespond);
Note that you name the class that should respond to the event as the only argument within ()
The class of the object that responds to an event must contain a method that accepts the event object created by the user’s action

34. In other words,…
When you register a component (such as a JFrame) to be a listener for events generated by another component (such as a JCheckBox), you must write a method that reacts to any generated event.
You cannot choose just any name for the reacting methods—specific methods react to specific events types, as listed below

35. Listener
Method
ActionListener
actionPerformed(ActionEvent)
AdjustmentListener
adjustmentValueChanged(adjustmentEvent)
FocusListener
focusGained(FocusEvent) and focusLost(FocusEvent)
ItemListener
itemStateChanged(ItemEvent)

36. Remember these three points….
When you declare a class that handles an event, you create the class to either implement a listener interface or extend a class that implements a listener interface..
Example…
Public class MYFrame extends JFrame implements ItemListener

37. And remember to ….
Register an instance of the event handler class as a listener for one or more components. For example,…
myCheckBox.addItemListener(this);

38. And…
Write a method that accepts the generated event and reacts to it. For example:
Public void itemStateChanged(ItemEvent event) {
// code that executes when ever the event occurs }

39. Notes….
If you fail to include an actionPerformed() method in a program that implements ActionListener, the program does not compile

40. Still more notes…
If more than one component generates an event, you usually want to figure out which component generated the specific event, so you decide which action to take

41. You can use the getSource() method to determine the component that sent the event
The following actionPerformed() method gets the source of the event and then compares it to a JButton named oneButton, which takes one action if the JButton is the source of the event and a different action if some other component is the source of the event

42. The method described above follows
Public void actionPerformed(ActionEvent event) {
Object source = event.getSource();
If(Source == oneButton)
// take some action
Else
// take some other action }

43. Using the JCheckBox Class
A JCheckBox consists of a label postioned beside a square
You click the square to display or remove a check mark
This turns an option on or off
The code for an application that uses four JCheckBoxes is shown below

44. import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class CheckBoxDemonstration extends JFrame implements ItemListener {
FlowLayout flow = new FlowLayout();
JLabel label = new JLabel("What would you like to drink?");
JCheckBox coffee = new JCheckBox("Coffee", false);
JCheckBox cola = new JCheckBox("Cola", false);
JCheckBox milk = new JCheckBox("Milk", false);
JCheckBox water = new JCheckBox("Water", false);
String output, insChosen;
JPanel panel = new JPanel();
Container con;
public CheckBoxDemonstration()
super("CheckBox Demonstration");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
con = getContentPane();
con.add(panel);
panel.setLayout(flow);
label.setFont(new Font("Arial", Font.ITALIC, 22));
coffee.addItemListener(this);

45. cola.addItemListener(this);
milk.addItemListener(this);
water.addItemListener(this);
panel.add(label);
panel.add(coffee);
panel.add(cola);
panel.add(milk);
panel.add(water); }
public static void main(String[] arguments) {
final int FRAME_WIDTH = 350;
final int FRAME_HEIGHT = 120;
CheckBoxDemonstration frame =
new CheckBoxDemonstration();
frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
frame.setVisible(true);
public void itemStateChanged(ItemEvent check)
// Actions based on choice go here

46. In the code above, the JLabel and JCheckBox objects are added to a JPanel and the JPanel is added to the Container that serves as the content pane

47. Constructors for CheckBoxes
JCheckBox box 1 = new JCheckBox();
//No label, unchecked
JCheckBox box 1 = new JCheckBox(“Check here”);
//label, unchecked
JCheckBox box 1 = new JCheckBox(“Check here”, false);
JCheckBox box 1 = new JCheckBox(“Check here”, true);
//label, checked

48. Using the ButtonGroup Class
You use this when you want options to be mutually exclusive
When you create aButtonGroup, you can group several components, such as JCheckBoxes are automatically turned off when the user selects any one check box

49. Inheritance hierarchy for ButtonGroup
Java.lang.Object
Java.swing.ButtonGroup

50. To create a ButtonGroup and then add a JCheckBox, you perform these steps:
ButtonGroup aGroup = new ButtonGroup();
Create a JCheckBox:
JCheckBox aBox = new JCheckBox();
Add aBox to aGroup:
aGroup.add(aBox);

51. Clearly, you have to add all of the individual check boxes to the ButtonGroup with the add() method
It doesn’t make any difference which you create first

52. Using the JComboBox Class
A JComboBox is a component that combines two features—a display area showing an option and a dropdown list box containing additional options.

53. You can build a JComboBox …
By using a constructor with no arguments and then adding items to the list with the addItem() method

54. JComboBox majorChoice = new JComboBox();
majorChoice.addItem(“English”);
majorChoice.addItem(“Math”);
majorChoice.addItem(“Sociology”);

55. Creating JScrollPanes
Allows a pane to be scrolled when it is too small to hold all of the content
Provides scroll bars along the side or bottom of a pane, or both, so that the user can scroll initially invisible parts of the pane into view

56. Inheritance hierarchy of the JScrollPane class
Java.lang.Object
Java.awt.Component
Java.awt.Container
Javax.swing.JComponent
Javax.swing.JScrollPane

57. There are four JScrollPane constructors
JScrollPane() creates an empty JScrollPane with scroll bars when needed
JScrollPane(Component) creates a JScrollPane that displays the contents of the specified component
JScrollPane(Component, int, int) creates a JScrollPane that displays the contents of the specified component
JScrollPane(int, int) creates a JScrollPane with both vertical and horizontal scroll bar specifications

58. import javax.swing.*;
import java.awt.*;
public class JScrollDemo extends JFrame {
JPanel panel = new JPanel();
JScrollPane scroll = new JScrollPane(panel,
ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,
ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
JLabel label = new JLabel("Event Handlers Incorporated");
Font bigFont = new Font("Arial", Font.PLAIN, 20);
Container con;
public JScrollDemo()
super("JScrollDemo");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
con = getContentPane();
label.setFont(bigFont);
con.add(scroll);
panel.add(label); }
public static void main(String[] args)
final int WIDTH = 180;
final int HEIGHT = 100;
JScrollDemo aFrame = new JScrollDemo();
aFrame.setSize(WIDTH, HEIGHT);
aFrame.setVisible(true);

59. Understanding When to Use getContentPane()
When you use JAVA 5 or later, you are allowed to add Components directly to JFrames and JApplets without explicitly calling getContentPane()
You can also use the remove() and setLayout() methods without an explicit call to getContentPane()

60. import java.awt.*;
import javax.swing.*;
public class JFrameWithContentCall extends JFrame {
final int SIZE = 180;
Container con = getContentPane();
JButton button = new JButton("Press Me");
public JFrameWithContentCall()
super("Frame");
setSize(SIZE, SIZE);
setVisible(true);
con.setLayout(new FlowLayout());
con.add(button); }
JFrameWithContentCall Class

61. import java.awt.*;
import javax.swing.*;
public class JFrameWithoutContentCall extends JFrame {
final int SIZE = 180;
JButton button = new JButton("Press Me");
public JFrameWithoutContentCall()
super("Frame");
setSize(SIZE, SIZE);
setVisible(true);
setLayout(new FlowLayout());
add(button); }
JFrameWithoutContentCall class

62. The main class..calling the above
Public class TestFramesWithAndWithout {
Public static void main(String[] args)
JFrameWithContentCall f1 = new JFrameWithContentCall();
JFrameWithoutContentCall f2 = new JFrameWithoutContentCall(); }

63. It is convenient that when you call add(button) from within the JFrameWithoutContentCall class, you do not have to create the container object con
In the newer versions of Java, in effect, you are calling this.getContentPane().add(button), but you are allowed to write the statement more simply.
The same is true for any calls to the setLayout() and remove() methods

64. However…
When you want to do something other than add(), setLayout(), or remove(), the JFrameWithoutContentCall CLASS does not work—it will compile and execute but it will not do the thing you request, like change the color of the background