Transcript Creating a Swing

Chapter 9: Visual
Programming Basics
Object-Oriented Program
Development Using Java:
A Class-Centered
Approach
Objectives

Event-Based Programming

Creating a Swing-Based Window

Adding a Window Closing Event Handler

Adding a Button Component
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Common Programming Errors
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Event-Based Programming
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Event-based programs provide fully
functioning GUIs
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An event is initiated by a user action
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A program must:
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Correctly assess which specific event has
occurred
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Provide the appropriate code to perform an action
based on the identified event
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Event-Based Programming (continued)
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Actions that trigger events include:
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Placing the mouse pointer over a button and
clicking the left mouse button
Using the TAB key until the desired button is
highlighted with a dotted line then pushing the
Enter key
Pressing an accelerator key (shortcut key)
The sequence of events in a program are
controlled by the user
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Event-Based Programming
(continued)
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
Programmer provides:
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Code to create GUI
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Code to appropriately process events
Java provides a set of objects for coding
GUIs:
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AWT (abstract window toolkit)
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Older GUI components
Swing
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Newer GUI components
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Swing Components
Examples
 Top-Level Container – JFrame, JApplet,
JWindow
 Intermediate Container – JPanel,
JInternalFrame
 Atomic – JButton, JCheckBox, JTextField
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The Event-Based Model
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Operating system:
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Has total control of computer
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Never relinquishes control to any executing
programs
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Most executing programs spend the
majority of their time in a sleep type of
mode
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When an event occurs:
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The operating system passes event
information to the appropriate application
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Permits the application to take action
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Containment Hierarchy
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Hierarchy of component placement
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Consists of one and only one top-level container
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Any number of other intermediate containers
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And/or atomic components
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JFrame is most commonly used as a top-level
container
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Heavyweight components (earlier Java term = toplevel containers) are responsible for interfacing with
the operating system
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Containment Hierarchy (continued)
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A content pane (next level of hierarchy) is an
internal component provided by each toplevel container
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All of the visible components displayed by a
GUI must be placed on a content pane
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Menu bar:
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Can be optionally added to a top-level container
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Placed outside of a content pane
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Containment Hierarchy
(continued)
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Layout manager:
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Defines how components are positioned and
sized within a container’s content pane
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Default placement can always be changed
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By explicitly specifying another layout manager
Lightweight components:
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Intermediate containers and atomic components
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Do not interface with the operating system
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JFrame automatically
provides a root pane, which
in turn contains the content
pane. Generally, not
concerned with root pane.
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Layout managers
Each top and intermediate-level containers has
a default layout manager that defines the
components position and size withing the
container’s content pane. You can always
change the default layout by specifying
another layout manager (chapter 10).
The six layout managers currently available
are:
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Lightweight Components
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intermediate containers and atomic
components
do not interface directly with the operating
system (hence lightweight)
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Creating a Swing-Based
Window
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Two predominant approaches:
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Construct a GUI as a separate class using Swing
components
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Construct a GUI object using Swing components
from within the main() method
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Creating a Swing-Based
Window (continued)
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Create JFrame:
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JFrame mainFrame = new JFrame("First GUI Window");
Setting size:
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syntax: objectReferenceName.setSize(width, height)
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mainFrame.setSize(300,150);
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Could also use a single statement
jFrame mainFrame = new JFrame(“First Gui Window”);
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Creating a Swing-Based
Window (continued)
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Display JFrame:
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Use show()
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Or setVisible(true)
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import javax.swing.*;
public class FirstWindow extends JFrame
{
private JFrame mainFrame;
public FirstWindow() // a constructor
{
mainFrame = new JFrame("First GUI Window");
Provides access to
all public and
protected methods
in the JFrame class
mainFrame.setSize(300,150);
mainFrame.show();
}
public static void main(String[]args)
{
new FirstWindow();
}
} // end of class
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Look and Feel
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Refers to:
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How a GUI appears on screen
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How a user interacts with it
Swing package:
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Supports four look and feel types
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If no look and feel is specified, the default Java
look and feel is used
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To implement a specific look and feel, this code must be
contained in a try and catch block.
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