Events and GUI Interfaces

Event Handler Methods

Text field ObjectResponder

JAVA AWT Environment: Messages are sent between JAVA Objects

Screen

Event Notification

Press Button(Buttons other objects generate events: Source)

Object e.g. button

OS Interrupt

Listener or middleman(interface)

Generates an Event

GUI Components and Screen Design

GUI Demo

Message

Hello World

CloseClearDisplay

Panel Instance

Textfield Instance

Label Instance

Button Instance

Frame Instance

JButton button = new JButton("Add Interest"); JLabel label = new JLabel("balance: " +

account.getBalance()); JPanel panel = new JPanel() or extends JPanel;panel.add(button); panel.add(label); frame.add(panel);

(or the class that extends a panel)frame.add (aClass);

Screen Design

Layout Managers

Predefined Layout Manager Subclasses

FlowLayout GridLayout BorderLayout BoxLayout CardLayout GridBagLayout

Layout Managers

Every container has a default layout manager

Programmer can set the layout manager as well

Each layout manager has its own particular rules governing how components will be arranged

setLayout () method

panel.setLayout (new BorderLayout() );

Border Layout (default for JFrame)

Defines five areas or regions into which components can be added

North

South

Center EastWest

BorderLayout (default for JFrame)package buttonapp;import javax.swing.Jframe;public class ButtonTester {

public static void main(String[] args) {

JFrame frame;ButtonPanel b = new ButtonPanel ();frame = new JFrame ("Button Frame");

frame.setSize(300, 400); frame.setDefaultCloseOperation

(javax.swing.JFrame.EXIT_ON_CLOSE);// frame.add(b);// or frame.add (b, BorderLayout.CENTER);

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

}

ButtonPanelpackage buttonapp;import javax.swing.JButton;import javax.swing.JPanel;public class ButtonPanel extends JPanel {

private JButton button1;public ButtonPanel ()

{button1 = new JButton ("Click Me");this.add(button1); }

}}

Flow Layout Flow layout puts as many components as possible

on a row, then moves to the next row Rows are created as needed to accommodate all of

the components Components are displayed in the order they are

added to the container Each row of components is centered horizontally in

the window by default, but could also be aligned left or right

Also, the horizontal and vertical gaps between the components can be explicitly set

Grid Layout A grid layout presents a container’s components in a rectangular

grid of rows and columns

One component is placed in each cell of the grid, and all cells have the same size

As components are added to the container, they fill the grid from left-to-right and top-to-bottom (by default)

The size of each cell is determined by the overall size of the container

setLayout (new GridLayout (<row>, <col>)

LAB

Project 31. SmartButton2. Passing a panel as

a parameter

Choices

• Radio buttons • Check boxes • Combo boxes

Radio Buttons

• mutually exclusive choices • When a button is selected, previously selected

button in set is automatically turned off

Radio Buttons (example from WileyPlus)

JRadioButton smallButton = new JRadioButton("Small"); JRadioButton mediumButton = new JRadioButton("Medium");JRadioButton largeButton = new JRadioButton("Large");

// Add radio buttons into a ButtonGroup so that // only one button in group is on at any time ButtonGroup group = new ButtonGroup(); group.add(smallButton); group.add(mediumButton); group.add(largeButton);

Radio Buttons

• Button group does not place buttons close to each other on container

• It is your job to arrange buttons on screen • isSelected: called to find out if a button is currently selected or

not

if(largeButton.isSelected()) size = LARGE_SIZE • Call setSelected(true) on a radio button in group before

making the enclosing frame visible

Border Examples

•

JPanel panel = new JPanel(); panel.setBorder(new EtchedBorder());

panel.setBorder(new TitledBorder(new EtchedBorder(), "Size"));

Border with a title