1. Components

2. Objectives: Learn about the Java Layout Managers.
Learn how to use Light Weight Components.
Learn how to implement an ActionListener.
An unstated objective is to get a feel for the big-O of different algorithms without introducing this concept formally.

3. Java Layout Managers

4. Java Layout Managers
The Java Layout Managers are a collection of classes that know how to lay out Containers.
Every container has a default Layout Manager.

5. BorderLayout
A BorderLayout lays out a container, arranging and resizing its components to fit in five regions: north, south, east, west, and center.
Each region may contain no more than one component, and is identified by a corresponding constant: NORTH, SOUTH, EAST, WEST, and CENTER.
When adding a component to a container with a border layout, you must use an add( ) method that takes the object to be added as the first argument, and one of these five constants as a second argument.

6. BorderLayout JPanel northPanel = new JPanel();
add(northPanel, BorderLayout.NORTH);
The following example shows a JFrame containing five JPanel’s, one in each area.

7. BorderLayout is the default layout for all frames and windows.

8. FlowLayout
A flow layout arranges components in a directional flow, much like lines of text in a paragraph. The flow direction is determined by the container's componentOrientation property and may be one of two values:
ComponentOrientation.LEFT_TO_RIGHT
ComponentOrientation.RIGHT_TO_LEFT
Flow layouts are typically used to arrange buttons in a panel. It arranges buttons horizontally until no more buttons fit on the same line. The line alignment is determined by the align property. The possible values are:
LEFT
RIGHT
CENTER
LEADING
TRAILING
Default
Default

9. FlowLayout is the default layout for all panels.

10. JPanel panel = new JPanel(new GridLayout(3, 4));
The GridLayout class is a layout manager that lays out a container's components in a rectangular grid. The container is divided into equal-sized rectangles, and one component is placed in each rectangle. For example, the following code creates a JPanel that contains 3 rows and 4 columns:
JPanel panel = new JPanel(new GridLayout(3, 4));

11. Light Weight Components

12. JComponents
JComponent is an object having a graphicical representation that can be displayed on the screen and that can interact with the user. Examples of components are the buttons, textfields, checkboxes, and scrollbars of a typical graphical user interface.

13. JComponents Method Summary Color getBackground()
Gets the background color of this component.
Graphics
getGraphics() Returns this component's graphics context, which lets you draw on a component.
int
getHeight() Returns the current height of this component.
String
getText() Returns the text contained in this TextComponent.
getWidth() Returns the current width of this component.
void
paint(Graphics g)
Paints this component.
paintComponent(Graphics g) Paints this component. Called by the paint method.
repaint()
Repaints this component.

14. JComponents Method Summary void setBackground(Color bg)
Sets the background color of this component.
setDoubleBuffered(boolean aFlag)
Sets whether this component should us a buffer to paint.
setForeground(Color fg) Sets the foreground color of this component.
setBorder(Border border) Sets the border of this component.
setEnabled(boolean enabled) Sets whether or not this component is enabled.
 void
setFont(Font f) Sets the font for this component.
setLayout(LayoutManager manager)
Sets the LayoutManager.
setPreferredSize(Dimension preferredSize)
Sets the preferred size of this component.
setSize(int width, int height)
Resizes this component so that it has width width and height height.
setText(String t) Sets the text of this TextComponent to the specified text.
setVisible(boolean aFlag) Makes the component visible or invisible.

15. JPanel

16. JPanel
JPanel is a generic light weight component. It can be used as a container to hold other light weight components or as a drawing surface.

17. JPanel vs JComponent Opaque Double Buffered Background Color
LayoutManager
JComponent
false
null
JPanel
true
Default Color
FlowLayout

18. Top Down Design

19. Top Down Programming Start JCreator.
Create a new file called “Lab21.java”.
Save the new file in your Lab21 folder.

20. Top Down Programming
package components; import java.awt.*; import javax.swing.*; public class Lab21 extends JFrame { }

21. Top Down Programming
main()

22. Top Down Programming
public class Lab21 extends JFrame { public static void main(String[] args) { Lab21 lab = new Lab21(); lab.setVisible(true); }

23. Top Down Programming
Constructor

24. Top Down Programming
public class Lab21 extends JFrame { public static void main(String[] args) { Lab21 lab = new Lab21(); lab.setVisible(true); } public Lab21() { setSize(400, 300); setTitle(“Components”); initTextFields(); initButton(); initMenu();

25. Top-Down Programming (cont’d)
initTextFields(), initButton(), and initMenu() will be used to add components to this JFrame object.

26. Top-Down Programming (cont’d)
public void initTextFields() { } public void initButton() public void initMenu()

27. initTextFields
public void initTextFields() { JPanel center = new JPanel(); center.setLayout(new FlowLayout(FlowLayout.LEFT)); center.setBackground(Color.yellow); add(center, BorderLayout.CENTER); }
BorderLayout is the
default LayoutManager
for the JFrame class.

28. JPanel
Notice that the panel placed in the center quadrant is taking up the entire frame.

29. JTextField

30. JTextField
JTextField is a lightweight component that allows the editing of a single line of text.
Constructor Summary
JTextField() Constructs a new TextField.
JTextField(Document doc, String text, int columns) Constructs a new JTextField that uses the given text storage model and the given number of columns.
JTextField(int columns) Constructs a new empty TextField with the specified number of columns.
JTextField(String text) Constructs a new TextField initialized with the specified text.
JTextField(String text, int columns) Constructs a new TextField initialized with the specified text and columns.

31. JTextField Method Summary String
getSelectedText() Returns the selected text contained in this TextComponent.
void
setEditable(boolean b)
Sets the specified boolean to indicate whether or not this TextComponent should be editable.
setHorizontalAlignment(int alignment) Sets the horizontal alignment of the text. Valid keys are:
JTextField.LEFT
JTextField.CENTER
JTextField.RIGHT

32. JTextField
public class Lab21 extends JFrame { private JTextField text1 = new JTextField(“”, 32); private JTextField text2 = new JTextField(“”, 32); public static void main(String[] args) { new Lab20(); } public Lab20() { /* code not shown */

33. initTextFields
public void initTextFields() { JPanel center = new JPanel(); center.setLayout(new FlowLayout(FlowLayout.LEFT)); center.setBackground(Color.yellow); center.add(text1); center.add(text2); add(center, BorderLayout.CENTER); }
FlowLayout.CENTER is the
default LayoutManager
for the JPanel class.

34. JTextField

35. JLabel

36. JLabel
Jlabel can display either text, an image, or both. You can specify where in the label's display area the label's contents are aligned by setting the vertical and horizontal alignment. By default, labels are vertically centered in their display area. Text-only labels are leading edge aligned, by default; image-only labels are horizontally centered, by default.

37. JLabel Constructor Summary
JLabel() Creates a JLabel instance with no image and with an empty string for the title.
JLabel(Icon image) Creates a JLabel instance with the specified image.
JLabel(Icon image, int horizontalAlignment) Creates a JLabel instance with the specified image and horizontal alignment.
JLabel(String text) Creates a JLabel instance with the specified text.
JLabel(String text, Icon icon, int horizontalAlignment) Creates a JLabel instance with the specified text, image, and horizontal alignment.
JLabel(String text, int horizontalAlignment) Creates a JLabel instance with the specified text and horizontal alignment.

38. JLabel Method Summary Icon. getIcon() Returns the default icon. void
setHorizontalAlignment(int alignment) Sets the horizontal alignment of the text. Valid keys are:
SwingConstants.LEFT
SwingConstants.CENTER
SwingConstants.RIGHT
setIcon(Icon defaultIcon) Sets the button's default icon.

39. initTextFields
In a FlowLayout objects
are arranged in the order
they are added.
public void initTextFields() { JPanel center = new JPanel(); center.setLayout(new FlowLayout(FlowLayout.LEFT)); center.setBackground(Color.yellow); center.add(new JLabel(“First Text Field:”)); center.add(text1); center.add(new JLabel(“Second Text Field:”)); center.add(text2); add(center, BorderLayout.CENTER); }

40. JLabel
In FlowLayout objects are arranged in the order in which they are added. The default alignment is FlowLayout.CENTER.

41. JButton

42. JButton
JButton is an implementation of a "push" button. Buttons can be configured, and to some degree controlled, by Actions. To configure a button to respond to user input (i.e. mouse clicks) you must add an ActionListener to each button.
Constructor Summary
JButton() Creates a button with no set text or icon.
JButton(Action a) Creates a button where properties are taken from the Action supplied.
JButton(Icon icon) Creates a button with an icon.
JButton(String text) Creates a button with text.
JButton(String text, Icon icon) Creates a button with initial text and an icon.

43. JButton Method Summary void
addActionListener(ActionListener l) Adds an ActionListener to the button.
Icon.
getIcon() Returns the default icon.
void
setIcon(Icon defaultIcon) Sets the button's default icon.

44. initButton
private void initButton() { }

45. initButton
private void initButton() { JPanel south = new JPanel(); }

46. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); }

47. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); }

48. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); JButton copy = new JButton(“Copy”); }

49. initButton
We need an import statement to use the swing Borders:
import javax.swing.border.BevelBorder;
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); JButton copy = new JButton(“Copy”); copy.setBorder(new BevelBorder(BevelBorder.RAISED)); }

50. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); JButton copy = new JButton(“Copy”); copy.setBorder(new BevelBorder(BevelBorder.RAISED)); copy.setPreferredSize(new Dimension(60, 30)); }

51. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); JButton copy = new JButton(“Copy”); copy.setBorder(new BevelBorder(BevelBorder.RAISED)); copy.setPreferredSize(new Dimension(60, 30)); south.add(copy); }

52. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); JButton copy = new JButton(“Copy”); copy.setBorder(new BevelBorder(BevelBorder.RAISED)); copy.setPreferredSize(new Dimension(60, 30)); south.add(copy); add(south, BorderLayout.SOUTH); }

53. JButton

54. ActionListener Interface
The listener interface for receiving action events. Any class that is interested in processing an action event implements this interface, and the object created with that class is registered with a component, using the component's addActionListener method. When the action event occurs, that object's actionPerformed method is invoked.
Method Summary
 void
actionPerformed(ActionEvent e)           Invoked when an action occurs.

55. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); JButton copy = new JButton(“Copy”); copy.setBorder(new BevelBorder(BevelBorder.RAISED)); copy.setPreferredSize(new Dimension(60, 30)); copy.addActionListener( ); south.add(copy); add(south, BorderLayout.SOUTH); }
We need an import statement to use the ActionListener interface:
import java.awt.event.*;

56. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); JButton copy = new JButton(“Copy”); copy.setBorder(new BevelBorder(BevelBorder.RAISED)); copy.setPreferredSize(new Dimension(60, 30)); copy.addActionListener( ); south.add(copy); add(south, BorderLayout.SOUTH); }

57. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); JButton copy = new JButton(“Copy”); copy.setBorder(new BevelBorder(BevelBorder.RAISED)); copy.setPreferredSize(new Dimension(60, 30)); copy.addActionListener(new ActionListener() { }); south.add(copy); add(south, BorderLayout.SOUTH); }

58. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); JButton copy = new JButton(“Copy”); copy.setBorder(new BevelBorder(BevelBorder.RAISED)); copy.setPreferredSize(new Dimension(60, 30)); copy.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { } }); south.add(copy); add(south, BorderLayout.SOUTH);

59. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); JButton copy = new JButton(“Copy”); copy.setBorder(new BevelBorder(BevelBorder.RAISED)); copy.setPreferredSize(new Dimension(60, 30)); copy.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { String text = text1.getText(); } }); south.add(copy); add(south, BorderLayout.SOUTH);

60. initButton
private void initButton() { JPanel south = new JPanel(); south.setPreferredSize(new Dimension(400, 40)); south.setBackground(Color.cyan); JButton copy = new JButton(“Copy”); copy.setBorder(new BevelBorder(BevelBorder.RAISED)); copy.setPreferredSize(new Dimension(60, 30)); copy.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { String text = text1.getText(); text2.setText(text); } }); south.add(copy); add(south, BorderLayout.SOUTH);

61. ActionListener
Click on the Copy button.

62. Menus

63. Menus Menus are made up of three parts.
JMenuBar which is attached to a JFrame via the setJMenuBar method..
JMenu which is added to the JMenuBar (more than one can be added).
JMenuItem which is added to the JMenu (more than one can be added.

64. initMenu
public void initMenu() { }

65. initMenu
public void initMenu() { JMenuBar menuBar = new JMenuBar(); }

66. initMenu
public void initMenu() { JMenuBar menuBar = new JMenuBar(); JMenu file = new JMenu("File"); }

67. initMenu
public void initMenu() { JMenuBar menuBar = new JMenuBar(); JMenu file = new JMenu(“File”); JMenuItem exit = new JMenuItem(“Exit”); }

68. initMenu
public void initMenu() { JMenuBar menuBar = new JMenuBar(); JMenu file = new JMenu(“File”); JMenuItem exit = new JMenuItem(“Exit”); exit.addActionListener( ); }

69. initMenu
public void initMenu() { JMenuBar menuBar = new JMenuBar(); JMenu file = new JMenu(“File”); JMenuItem exit = new JMenuItem(“Exit”); exit.addActionListener( ); }

70. initMenu
public void initMenu() { JMenuBar menuBar = new JMenuBar(); JMenu file = new JMenu(“File”); JMenuItem exit = new JMenuItem(“Exit”); exit.addActionListener(new ActionListener() { }); }

71. initMenu
public void initMenu() { JMenuBar menuBar = new JMenuBar(); JMenu file = new JMenu(“File”); JMenuItem exit = new JMenuItem(“Exit”); exit.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { } });

72. initMenu
public void initMenu() { JMenuBar menuBar = new JMenuBar(); JMenu file = new JMenu(“File”); JMenuItem exit = new JMenuItem(“Exit”); exit.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { System.exit(0); } });

73. initMenu
public void initMenu() { JMenuBar menuBar = new JMenuBar(); JMenu file = new JMenu(“File”); JMenuItem exit = new JMenuItem(“Exit”); exit.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { System.exit(0); } }); file.add(exit);

74. initMenu
public void initMenu() { JMenuBar menuBar = new JMenuBar(); JMenu file = new JMenu(“File”); JMenuItem exit = new JMenuItem(“Exit”); exit.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { System.exit(0); } }); file.add(exit); menuBar.add(file);

75. initMenu
public void initMenu() { JMenuBar menuBar = new JMenuBar(); JMenu file = new JMenu(“File”); JMenuItem exit = new JMenuItem(“Exit”); exit.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { System.exit(0); } }); file.add(exit); menuBar.add(file); setJMenuBar(menuBar);

76. Menus
Click on the Exit menu item to close the frame.

77. Questions?

78. Begin Lab 22

79. MyNumberField for Lab22A
Extending JTextField
MyNumberField for Lab22A

80. import javax.swing.JTextField;
import javax.swing.border.BevelBorder;
import java.awt.event.*;
public class MyNumberField extends JTextField { }

81. public MyNumberField(int columns) {
super(columns);
setBorder(new BevelBorder(BevelBorder.LOWERED));
setHorizontalAlignment(JTextField.CENTER);
addKeyListener(new KeyAdapter() {
@Override
public void keyTyped(KeyEvent e) {
char c = e.getKeyChar();
if (!(Character.isDigit(c) ||
(c == KeyEvent.VK_BACK_SPACE) ||
(c == KeyEvent.VK_DELETE)))
e.consume(); }
});

82. public void setValue(int n) {
setText(String.valueOf(n)); }
public int getValue() {
try {
return Integer.parseInt(getText());
catch (NumberFormatException e)
return 0;

83. Declaring An Instance Of MyNumberField
MyNumberField width = new MyNumberField(24);