Object-Oriented Software Engineering

JFrames with Swing

22UniS

Contents

• JFrame

• Content Pane

• Layout Managers

• Java Interfaces

• ActionListeners

33UniS

JFrameAny interesting GUI will use the JFrame class.

public class FrameDemo { private static void createAndShowGUI() { JFrame.setDefaultLookAndFeelDecorated(true);

JFrame frame = new JFrame("FrameDemo"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

JLabel emptyLabel = new JLabel(""); emptyLabel.setPreferredSize(new Dimension(175, 100)); frame.getContentPane().add(emptyLabel, BorderLayout.CENTER);

frame.pack(); frame.setVisible(true); } public static void main(String[] args) { javax.swing.SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } }); }}

44UniS

JFrameprivate static void createAndShowGUI() { JFrame.setDefaultLookAndFeelDecorated(true);

JFrame frame = new JFrame("FrameDemo"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

JLabel emptyLabel = new JLabel(""); emptyLabel.setPreferredSize(new Dimension(175, 100)); frame.getContentPane().add(emptyLabel, BorderLayout.CENTER);

frame.pack(); frame.setVisible(true); }

55UniS

JFrame

Problem is createAndShowGUI is declared static:

private static void createAndShowGUI()

Static methods can not reference any non-static variables.This includes any reference to a non-static class.

This has to be, because main has to be static, and can onlyreference static methods.

66UniS

JFrame

For example, move declaration of frame outside scopeof createAndShowGUI:

private JFrame frame;private static void createAndShowGUI() {

............frame = new JFrame("FrameDemo");............

}

$ javac FrameDemo.javaFrameDemo.java:10: non-static variable frame cannot be referenced from a static context frame = new JFrame("FrameDemo");

77UniS

Content Pane

The menu bar and content pane provide functionalityfor a JFrame.

88UniS

Content Pane, JPanel

public class MyContents extends JPanel {public MyContents ( ) {// put contents of JFrame in this// non-static constructor method}private static void createAndShowGUI() {.....................JFrame frame = new JFrame("Person");.....................MyContents newContentPane = new MyContents( );.....................frame.setContentPane(newContentPane);.....................}

}

99UniS

Layout Managers

A JPanel must have a layout manager to control wherebuttons, icons, text areas etc are to be placed with respect toeach other inside the content pane.

newContentPane LayoutManager

BorderLayout

CardLayout

FlowLayout

GridLayout

GridBagLayout

JPanel

{ choice of } *

*

*

*

*

1010UniS

BorderLayout

Every content pane is initialized to use a BorderLayout.

BorderLayout has five areas. These areas are specified by the BorderLayout constants • PAGE_START, • PAGE_END, • LINE_START, • LINE_END, • and CENTER.

1111UniS

Code for adding buttons to BorderLayout

JButton button = new JButton("Button 1 (PAGE_START)"); newContentPane.add(button, BorderLayout.PAGE_START);

//Make the center component big, since that's the //typical usage of BorderLayout. button = new JButton("Button 2 (CENTER)"); button.setPreferredSize(new Dimension(200, 100)); newContentPane.add(button, BorderLayout.CENTER);

button = new JButton("Button 3 (LINE_START)");newContentPane.add(button, BorderLayout.LINE_START);

button = new JButton("Long-Named Button 4 (PAGE_END)"); newContentPane.add(button, BorderLayout.PAGE_END);

button = new JButton("5 (LINE_END)"); newContentPane.add(button, BorderLayout.LINE_END);

Code taken from Java tutorial, also on course website.

1212UniS

BorderLayout: Note

Behaviour of buttons depends on the object towhich it belongs.

In a later lecture we will see that buttons attached toJToolBar will seem to behave differently when the JToolBar is then attached toa BorderLayout within a JFrame!

1313UniS

BoxLayout

BoxLayout stacks components either as column or in row.

1414UniS

BoxLayout Code

public static void addComponentsToPane(Container pane) { pane.setLayout(new BoxLayout(pane, BoxLayout.Y_AXIS));

addAButton("Button 1", pane); addAButton("Button 2", pane); addAButton("Button 3", pane); addAButton("Long-Named Button 4", pane); addAButton("5", pane); }

private static void addAButton(String text, Container container) { JButton button = new JButton(text); button.setAlignmentX(Component.CENTER_ALIGNMENT); container.add(button); }

Code taken from Java tutorial, also on course website.

1515UniS

GridBagLayout

• GridBagLayout aligns components by placing them within a grid of cells

• Components can span more than one cell.

• The rows in the grid can have different heights, and grid columns can have different widths.

1616UniS

GridBagLayout

Grid (0,0) Grid (0,1) Grid (0,2)

Grid (1,0)

Grid (1,1)

Grid (1,2)

Grid (2,0) Grid (2,1) Grid (2,2)

1717UniS

GridBagLayout

JButton button;

pane.setLayout(new GridBagLayout());

GridBagConstraints c = new GridBagConstraints();

c.fill = GridBagConstraints.HORIZONTAL;

Constraint controls where buttons appear within the GridBagLayout.

Resizing component will causehorizontal space to be sharedacross buttons

1818UniS

GridBagLayout button = new JButton("Button 1"); c.gridx = 0; c.gridy = 0; pane.add(button, c);

button = new JButton("Button 2"); c.gridx = 1; c.gridy = 0; pane.add(button, c);

button = new JButton("Button 3"); c.gridx = 2; c.gridy = 0; pane.add(button, c);

button = new JButton("Long-Named Button 4"); c.ipady = 40; //make this component tall c.weightx = 0.0; c.gridwidth = 3; c.gridx = 0; c.gridy = 1; pane.add(button, c);

1919UniS

GridBagLayout

button = new JButton("5"); c.ipady = 0; //reset to default c.weighty = 1.0; //request any extra vertical space c.anchor = GridBagConstraints.PAGE_END; //bottom of space c.insets = new Insets(10,0,0,0); //top padding c.gridx = 1; //aligned with button 2 c.gridwidth = 2; //2 columns wide c.gridy = 2; //third row pane.add(button, c);

2020UniS

Event ListenersFor a class to provide interaction it might implement the ActionListener and/or the MouseInputListener interfaces in Java as well as extend JPanel.

MyNewClass

«interface» ActionListenerJPanel «interface»

MouseInputListener

JFrame

1

1..*

2121UniS

Java Interfaces

• Interface represents a contract defining a protocol.

• An interface is a named collection of method definitions, without implementations.An interface can also declare constants.

• An interface cannot implement any methods.

• An interface has no constructor.

• All interface methods are public.

• No static methods allowed.

• An interface is not part of the class hierarchy. Unrelated classes can implement the same interface.

• A class can implement many interfaces but can have only one superclass.

2222UniS

MouseInputListener and ActionListener <<interface>>

MouseInputListener

void mouseClicked (MouseEvent)

void mouseMoved (MouseEvent)

void mouseExited (MouseEvent)

void mouseReleased (MouseEvent)

void mouseEntered (MouseEvent)

void mousePressed (MouseEvent)

void mouseDragged (MouseEvent)

void actionPerformed(ActionEvent)

ActionListener

2323UniS

Handling Events

• GUI Components communicate with each other by sending events.

• A listener is an object that is notified when an eventoccurs and can examine the contents of that eventto perform some action.

Event Listener ObjectGUI Component

Eventfired by GUI

Registers to listen for particular type of events

2424UniS

Handling Events

Event Listener ObjectEvent Listener Object

Event Listener ObjectEvent Listener Object

Event Listener ObjectEvent Listener Object

GUI Component

• Any number of objects can register to listen forsame type of event

• Events are multicast to all objects that are• listening

Event

Event

Event

2525UniS

Common Events and their Listeners<<interface>>

java.util.EventListenerjava.awt.AWTEvent

MouseEvent

ActionEvent

<<interface>>

MouseListener

<<interface>>

MouseMotionListener

<<interface>> ActionListener

2626UniS

Listening For Events

aSource aListenerregister( )

anEvent<<create>>

query( )

notify(anEvent )

2727UniS