Graphical User Interface GUI Programming I

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Graphical User Interface (GUI) Programming I
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Lecture Objectives

• Understand the basic concepts of Graphical User
  Interfaces (GUIs)
• Practice Basic GUI Programming in Java
• Develop Basic GUI Applications
• Study Layout Management and Managers for GUI
  Applications

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Outline
Graphical User Interfaces (GUIs) -- Overview --
Essential elements Containers -- Overview --
Examples Components -- Overview --
Examples Layout Managers -- Overview --
Examples
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Graphical User Interface (GUI)

• A Graphical User Interface (GUI) is one variety
  of user interface.
• User interacts with objects on the screen
  (icons, buttons, scroll-bars, etc.) via mouse
  clicks or keyboard actions.

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GUI Popularity

• Popularized in 1980s by the Macintosh.
• Now state of the practice, and not final word in
  UI
• Intended to replace text-based "command line" and
  "function key" interfaces.
• Despite similarities, GUIs are typically
  platform-specific (Windows 95/98/NT/1900, MacOS,
  X Windows look-and-feel standards).
• Some graphical toolkits now provide
  cross-platform APIs. E.g. wxWindows, GTK, Java.

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Javas GUI Capabilities
Java provides essentially two related toolkits
for making GUIs The Abstract
Windowing Toolkit ("AWT"), and The
Java Foundation Classes ("Swing") Swing is
merely an expanded version of the AWT, and
provides greater control and convenience.
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Why Two Toolkits in Java?
MFC and always "BSoD"
AWT, then JFC or "Swing"
Well, its a long story. In short, JFC (swing)
is Suns answer to Microsofts MFC--a detailed
toolkit library.
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Cautionary Note

• Java has two flavors of toolkits
• Swing.
• AWT.
• It is not wise to mix AWT and Swing Components.
  For your first programs, stick with one toolkit
  (swing!!!).
• Well start off with AWT Components to show the
  basics.
• Then, we will switch to Swing Components.
• How do you tell them apart?
• Generally, but not always, Swing Components will
  have a
• "J" in front of the class name

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Keep in Mind

• We will program graphical elements in source
  code.
• There are drag and drop systems (graphical
  integrated development environments (IDEs).
• Java is designed to work across different
  platforms.
• This poses special challenges!!!
• As does the very nature of WIMP GUIs (windows,
  icons, menus, and pointing device graphic user
  interface)

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Steps to GUI Construction
We will learn GUI creation in two steps the
"view", and then the "controls" or event handling.
1.

• In Java, to create a GUI, you (1)
• Specify a Container, using . . .
• a Layout Manager to . . .
• place Components and/or Containers of
  Components . . . on the screen as desired.

i.e. UI form and appearance
TODAY
LATER
2.

• In Java, to make a GUI act as the
• interface for a program, you (2)
• Design human/computer dialog, using Listeners
  and component-generated events

i.e. UI interaction and behavior
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GUI Design Creation
There are three essential constructs in any GUI
Containers -- used to hold items (e.g., the
frame) Components -- the widgets or
interactors (e.g., buttons) LayoutManagers
-- the hidden algorithm used to organize the
widgets inside the container
offset
offset
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GUI Basic Constructs
The three basic constructs used in every GUI are
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Containers
STEP 1
Containers are special components that may
contain other components.
Note Containment is not the same as inheritance
extension. A Frame may contain buttons, but
buttons are not subclasses of Frame.
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Containers (Contd)

• A Container is a class that extends from
  java.awt.Container
• As it turns out, the class "Container" is itself
  a Component.
• Containers can have
• Layouts set on them (discussed later)
• Other components or containers added to them.

Object
Component
Container
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Containers An Example
Lets make a simple Frame. When working
with GUIs, you often have to consult the
API. Note the inheritance structure of your
classes.
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Containers An Example (Contd)
So far, weve used the API to learn how to make a
Frame. We found constructors for public Frame
() public Frame (String strTitle) Now, how
can we set the size of the Frame? We again
return to the API.
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Containers An Example (Contd)
The class java.awt.Frame does not contain a
method to set its size. But such a method was
inherited from java.awt.Component
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Containers An Example (Contd)
Likewise, theres no method in java.awt.Frame to
make the Frame visible. Instead, we find the
method "show()" was inherited from java.awt.Window
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Hello GUI The Program
import java.awt. public class HelloGUI
public static void main (String arg)
System.out.println("About to make GUI")
Frame f new Frame ("Hello GUIs")
f.setSize( 200, 200 ) f.show()
System.out.println("Finished making GUI") //
main() // class HelloGUI
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Hello GUI The Program (Contd)
Our program runs, and the frame never goes away.
When we reach the end of main (as our print
statement indicates) why doesnt the program end?

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Hello GUI The Program (Contd)
When the Java VM created our Frame, it entered
into a kind of infinite loop, waiting for
input and events. (This is common for all
graphical toolkits.)
while(true) //get user input // handle
event
Since we didnt write any event handlers, not
even the "window disposal" button will work.
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Hello GUI The Program (Contd)
Solution To fix this problem, well have to
write some event handling code. But in order to
write some event handling code, we have to create
some components So, for now, youll just have
to use Ctrl-C to end the program. Once the
basics of GUI construction are covered, well
return to this problem.
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GUI Design Idea
We really have two choices when working with
top-level containers
java.awt.Frame
MyGUI
MyGUI
java.awt.Frame
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GUI Design Idea Example
import java.awt. public class HelloComposition
Frame f public HelloComposition()
f new Frame("Composition Test")
f.setSize(200,200) f.setBackground(Color.
red) f.show() public static
void main(String args) HelloComposition h
new HelloComposition()
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GUI Design Idea Example
A few changes allows us to convert between the
two solutions
Note Even the statement this. could be safely
removed!
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Which Solution Works Better?
Composition
Inheritance

• Saves the single inheritance

• Use up our single inheritance

• "Wasted inheritance" occurs where we subclass,
  but fail to override anything.

• Useful when you want the "factory settings" for
  a GUI, with no changed behavior

• Easier to change basic GUI behavior

• Often requires more code, more references

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Container Summary

• Creating containers requires careful study of
  the API. Watch the inheritance structure of the
  classes.
• A top-level container, like a Frame, requires
  event handlers (covered later).
• There are many useful methods for customizing
  containers. Just look them up in the API
  documentation

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Container Summary
We may often use "composition" where --
We dont anticipate changing behaviors --
We need to save our single inheritance We may
often use "inheritance" where -- We
need to change basic GUI behaviors
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Components
STEP 2

• Most interactions in a Java GUI are with
  Components.
• Another generic term for Component in other GUIs
  
• (e.g. X Windows) is "widget".
• Different types of components for different
  types of
• interaction (e.g. buttons, etc.)
• User interactions with components create events
  (thus, allow event-driven programming)
• As a rule, a Component cannot have other
  components inside
• Exceptions to rule pop up menus may have menu
  items added to them. And Containers are
  themselves components due to inheritance.

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Component Examples
Demo HelloWidget
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Component Examples (Contd)
Component - generic widget that you can
interact with Button - a widget
that you can press Canvas - a
widget that you can draw on Checkbox -
a widget that is checked or not checked
Choice - an option menu that drops
down Container - a generic class that
contains Components Panel - a
Container to be used inside another
container used to split an
existing window Label - a
single line of read-only text List
- a list of Strings Scrollbar
- a horizontal or vertical scrollbar
TextComponent TextArea - multi-line
editable text TextField -
single-line editable text
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Component Examples (Contd)

• Canvas
• Typically a drawing surface on which shapes,
  graphs, pictures, etc can be drawn.
• Utilize mouse events and mouse motion events to
  interact with the user to accomplish the drawing
  tasks.
• TextField
• A one-line data entry area.
• Theoretically infinite in length.
• Can generate Key events to indicate that the
  user has typed a key.
• More typically, it generates an Action event
  when the user finishes the data entry and hits
  Return in the TextField.

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Component Examples (Contd)

• Button
• Simply a clickable component.
• Appears as a standard button on whatever
  graphical environment the user happens to be
  running at the time.
• Generates an Action event when clicked.
• Label
• A one-line field of text.
• User cannot change this text directly program
  changes text with setText( ) method.
• Usually not used to capture events (but could).
• Usually used as a one-way information source to
  provide a message to the user.

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Joining Components Containers
Containers have a method public void
add (Component c) that allows us to place items
inside. Thus Panel p new Panel() Button
b1 new Button ("Example 1") Button b2 new
Button ("Example 2") p.add (b1)
p.add(b2) In this example, two buttons are
added to the panel.
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An Example
import java.awt. public class HelloComponent
Frame f public HelloComponent() f
new Frame("Component Test")
f.setSize(200,200) f.setBackground(Color.
red) Panel p new Panel()
Button b new Button("Hello Components")
p.add(b) f.add(p) f.show()
public static void main (String args)
new HelloComponent()
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Layout Managers
STEP 3
We can now create Components and Containers. But
how can they be organized? We might be tempted to
call methods that set the x, y location of a
component in a container. Consulting the API, we
find some likely methods public void
setLocation(int x, int y) public void
setSize(int width, int height)
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Layout Managers Motivation

• To arrange items, one could specify the location
  of a Component by specific x and y coordinates.
  The Component class contains the method
  setLocation(int width, int height)
• Frame f new Frame()
• f.setSize(500,500)
• Button myButton new Button ("Click")
• add(myButton)
• myButton.setLocation(25, 75)

Whats wrong with this approach???
NOTE Origin 0,0 at top left!
Note Buttons x and y coordinate starts from
top left
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Layout Managers Motivation (Contd)

• Problems with specifying (x, y) coordinates for
  Components
• This becomes tedious for even mildly complex
  GUIs.
• Addition of more components requires
  recalculation of every components x, y
  coordinate.
• If container resizes (e.g., user expands
  window), calculations have to be redone!
• Solution
• Position components based on a percentage of
  available container size. Or create an
  algorithm to place components . . .
• But Java already does this for you !!!

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Layout Managers AWT-Based

• Java provides several layout managers.
• We will concentrate here on several of them
• BorderLayout
• GridLayout
• FlowLayout
• BoxLayout
• To tell a container which layout manager to use,
  invoke the method
• setLayout( )
• and specify a type of layout.
• For example
• To specify a BorderLayout
• setLayout (new BorderLayout())

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Layout Managers Two General Flavors

• One can conceptually divide layout managers into
  two types
• Those that attach constraints to their
  components.
• Those that do not.
• What does this mean, "attach constraints?
• If a manager attaches constraints to a component,
  then information about a components location
  (e.g., compass points) is stored with the object.

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Layout Managers Constraints

• BorderLayout specifies constraints corresponding
  to compass regions of a container

NORTH
EAST
WEST
CENTER
SOUTH
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Layout Managers Constraints (Contd)

• BorderLayout then appends constraint information
  on all components, e.g.
• this.setLayout (new BorderLayout())
• Button e new Button ("East")
• Button w new Button ("West")
• Button n new Button ("North")
• add(e, "East") // deprecated
• add("West", w) // works deprecated
• add(n, BorderLayout.NORTH) // preferred

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Layout Managers Constraints (Contd)
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Layout Managers Another Example

• import java.awt.
• public class Test extends Frame
• public Test()
• super ("BorderLayout Demo")
• this.setSize(200,200)
• this.setLayout(new BorderLayout())
• this.add (new Button ("North"),
  BorderLayout.NORTH)
• this.add (new Button ("South"),
  BorderLayout.SOUTH)
• this.add (new Button ("East"),
  BorderLayout.EAST)
• this.add (new Button ("West"),
  BorderLayout.WEST)
• this.add (new Button ("Center"),
  BorderLayout.CENTER)
• public static void main (String args)
• new Test().show()
• // Test

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Layout Managers Another Example (Contd)

• Program Output

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BorderLayout
BorderLayout specifies the arrangement

• To add components to a BorderLayout, specify the
  position in which the component will reside.
• Only one component (or container) can go in each
  of the five positions.

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BorderLayout An Example
setLayout (new BorderLayout()) add(new Label
("Hello!"), "North") Canvas myCanvas new
Canvas() // more about Canvas in a moment add
(myCanvas, "Center")
Hello!
a fresh canvas for drawing here
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BorderLayout Simple Example
import java.awt. public class HelloLayout
public static void main(String args) Frame f
new Frame() f.setSize(400,400) BorderLayout
bord new BorderLayout() f.setLayout(bord) B
utton b new Button ("Hello") f.add(b,
BorderLayout.SOUTH) // HelloLayout
Will this work? Lets run it and find out...
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BorderLayout Simple Example (Contd)
import java.awt. public class HelloLayout
public static void main(String args) Frame f
new Frame() f.setSize(400,400) BorderLayout
bord new BorderLayout() f.setLayout(bord) B
utton b new Button ("Hello") f.add(b,
BorderLayout.SOUTH) f.show() //
HelloLayout
Ahh.. We forgot to set our Frame visible. Now
it works. Welcome to the exciting world of GUI
debugging.
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Layout Managers No Constraints

• The second type of LayoutManager does not specify
  constraints for the objects it holds.
• Examples
• GridLayout()
• FlowLayout()
• Without constraints, you cannot accurately
  predict layout behavior across platforms.

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Layout Managers No Constraints (Contd)

• import java.awt.
• public class FlowTest extends Frame
• String Labels "Short", "Short", "Long
  Label",
• "Really Long Label", "Really, really
  long"
• public FlowTest()
• this.setSize(400,200)
• setLayout(new FlowLayout())
• for (int i 0 i lt Labels.length i)
• Button temp new Button (Labelsi)
• add (temp)
• public static void main (String arg)
• new FlowTest().show()
• //class FlowTest

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Layout Managers No Constraints (Contd)
Program Output
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Layout Managers No Constraints (Contd)

• Program Output is also

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Layout Managers No Constraints (Contd)

• Note
• Since pixels, fonts and insets vary with each
  platform, layout without constraints will vary
  greatly.
• Lesson
• Use layout managers without constraints only when
  you have few components, or youve anticipated
  their possible movement.

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Layout Managers No Constraints (Contd)

• Dont think that layout managers without
  constraints are not useful!
• One of the most useful constraint-free layout
  manager is "GridLayout".
• public GridLayout()
• public GridLayout(int rows, int cols)
• public GridLayout(int rows, int cols, int hgap,
  int vgap)

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GridLayout
GridLayout specifies a grid pattern via
setLayout (new GridLayout (rows, columns)) For
example setLayout (new
GridLayout(2,3)) generates
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GridLayout (Contd)

• To add components (or containers) to a
  GridLayout, particular locations are not
  specified (unlike BorderLayout).
• Instead, the components (or containers) are
  positioned by the sequence in which they are
  added, as indicated by numerals below.
• Significantly, GridLayout is distortive, meaning
  components are stretched to fill the available
  space in the grid.

1
2
3
4
5
6
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GridLayout (Contd)
Optionally, two additional parameters may be used
with GridLayout to specify the horizontal and
vertical spacing (in pixels) between grid
elements
setLayout (new GridLayout (rows, columns,
hspace, vspace)) where hspace specifies
horizontal size, and vspace specifies vertical
size, e.g., setLayout (new
GridLayout (2, 2, 7, 5))
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GridLayout Example 1

• import java.awt.
• public class CalcPad extends Frame
• public CalcPad()
• setLayout(new GridLayout(5,3))
• add (new Button ("7"))
• add (new Button ("8"))
• add (new Button ("9"))
• add (new Button ("4"))
• add (new Button ("5"))
• add (new Button ("6"))
• add (new Button ("1"))
• add (new Button ("2"))
• add (new Button ("3"))
• add (new Button ("."))
• add (new Button ("0"))
• add (new Button ("/-"))
• add (new Panel())

public static void main (String args)
CalcPad ti new CalcPad()
ti.setSize(150,150) ti.show()
//CalcPad
Program Output
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GridLayout Example 2

• import java.awt.
• public class CalcPad extends Frame
• public CalcPad()
• setLayout(new GridLayout(5,3))
• int off-2,2,0
• for (int i9 i gt 1 i--)
• add (new Button (""(ioffi3)))
• add (new Button ("."))
• add (new Button ("0"))
• add (new Button ("/-"))
• add (new Panel())
• public static void main (String arg)
• CalcPad ti new CalcPad()
• ti.setSize(150,150)
• ti.show()
• //CalcPad

Program Output
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BoxLayout Motivation
Often, it is desirable to place items in
horizontal or vertical direction. A grid layout
may not be the best choice, since grid components
are resized to fit the available space--its a
distorts its contents.
container
component
A (3, 1) grid forces size changes
Desired look
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BoxLayout Manager
A BoxLayout provides this feature. It resembles
a FlowLayout, but with directional control, and
other features.
Horizontal and vertical flow control
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BoxLayout How?
The BoxLayout has a single constructor
BoxLayout(Container target, int axis) The
target is the container we wish to layout. The
axis is a static field
BoxLayout.X_AXIS BoxLayout.Y_AXIS JPane
l buttonPanel new JPanel() BoxLayout bLayout
new BoxLayout (buttonPanel,
BoxLayout.X_AXIS) buttonPanel.setLayout(bLayout)