AWT.pptx

AWT (Abstract Windowing Toolkit)
The AWT is roughly broken into three categories
Components
Layout Managers
Graphics
Many AWT components have been replaced by Swing
components
It is generally not considered a good idea to mix
Swing components and AWT components. Choose to
use one or the other.

AWT – Class Hierarchy
Panel
Button
Checkbox
Choice
Label
List
Component
Container Frame
Window
TextArea
TextField
TextComponent
Note: There are more classes, however,
these are what are covered in this chapter

Component
Component is the superclass of most of the displayable
classes defined within the AWT. Note: it is abstract.
MenuComponent is another class which is similar to
Component except it is the superclass for all GUI items
which can be displayed within a drop-down menu.
The Component class defines data and methods which
are relevant to all Components
setBounds
setSize
setLocation
setFont
setEnabled
setVisible
setForeground -- colour
setBackground -- colour

Container
Container is a subclass of Component. (ie. All containers
are themselves, Components)
Containers contain components
For a component to be placed on the screen, it must be
placed within a Container
The Container class defined all the data and methods
necessary for managing groups of Components
add
getComponent
getMaximumSize
getMinimumSize
getPreferredSize
remove
removeAll

Windows and Frames
The Window class defines a top-level Window with no
Borders or Menu bar.
Usually used for application splash screens
• Frame defines a top-level Window with Borders and a
Menu Bar
• Frames are more commonly used than Windows
Once defined, a Frame is a Container which can contain
Components
Frame aFrame = new Frame(“
”Hello World“
”);
aFrame.setSize(100,100);
aFrame.setLocation(10,10);
aFrame.setVisible(true);

Panels
When writing a GUI application, the GUI portion can
become quite complex.
To manage the complexity, GUIs are broken down into
groups of components. Each group generally provides a
unit of functionality.
A Panel is a rectangular Container whose sole purpose is
to hold and manage components within a GUI.
Panel aPanel = new Panel();
aPanel.add(new Button("Ok"));
aPanel.add(new Button("Cancel"));
Frame aFrame = new Frame("Button Test");
aFrame.setSize(100,100);
aFrame.setLocation(10,10);
aFrame.add(aPanel);

Buttons
This class represents a push-button which displays some
specified text.
When a button is pressed, it notifies its Listeners. (More
about Listeners in the next chapter).
To be a Listener for a button, an object must implement the
ActionListener Interface.
Button okButton = new Button("Ok");
Button cancelButton = new Button("Cancel");
aPanel.add(okButton));
aPanel.add(cancelButton));
okButton.addActionListener(controller2);
cancelButton.addActionListener(controller1);

Labels
This class is a Component which displays a single line of
text.
Labels are read-only. That is, the user cannot click on a
label to edit the text it displays.
Text can be aligned within the label
Label aLabel = new Label("Enter password:");
aLabel.setAlignment(Label.RIGHT);
aPanel.add(aLabel);

List
This class is a Component which displays a list of Strings.
The list is scrollable, if necessary.
Sometimes called Listbox in other languages.
Lists can be set up to allow single or multiple selections.
The list will return an array indicating which Strings are
selected
List aList = new List();
aList.add("Calgary");
aList.add("Edmonton");
aList.add("Regina");
aList.add("Vancouver");
aList.setMultipleMode(true);

Checkbox
This class represents a GUI checkbox with a textual label.
The Checkbox maintains a boolean state indicating whether
it is checked or not.
If a Checkbox is added to a CheckBoxGroup, it will behave
like a radio button.
Checkbox creamCheckbox = new CheckBox("Cream");
Checkbox sugarCheckbox = new CheckBox("Sugar");
[…
]
if (creamCheckbox.getState())
{
coffee.addCream();
}

Choice
This class represents a dropdown list of Strings.
Similar to a list in terms of functionality, but displayed
differently.
Only one item from the list can be selected at one time and
the currently selected element is displayed.
Choice aChoice = new Choice();
aChoice.add("Calgary");
aChoice.add("Edmonton");
aChoice.add("Alert Bay");
[…
]
String selectedDestination= aChoice.getSelectedItem();

TextField
This class displays a single line of optionally editable text.
This class inherits several methods from TextComponent.
This is one of the most commonly used Components in the
AWT
TextField emailTextField = new TextField();
TextField passwordTextField = new TextField();
passwordTextField.setEchoChar("*");
[…]
String userEmail = emailTextField.getText();
String userpassword = passwordTextField.getText();

TextArea
This class displays multiple lines of optionally editable text.
This class inherits several methods from TextComponent.
TextArea also provides the methods: appendText(),
insertText() and replaceText()
// 5 rows, 80 columns
TextArea fullAddressTextArea = new TextArea(5, 80);
[…
]
String userFullAddress= fullAddressTextArea.getText();

Layout Managers
Since the Component class defines the setSize() and
setLocation() methods, all Components can be sized and
positioned with those methods.
Problem: the parameters provided to those methods are
defined in terms of pixels. Pixel sizes may be different
(depending on the platform) so the use of those methods
tends to produce GUIs which will not display properly on
all platforms.
Solution: Layout Managers. Layout managers are
assigned to Containers. When a Component is added to
a Container, its Layout Manager is consulted in order to
determine the size and placement of the Component.
NOTE: If you use a Layout Manager, you can no longer
change the size and location of a Component through the
setSize and setLocation methods.

Layout Managers (cont)
There are several different LayoutManagers, each of which
sizes and positions its Components based on an algorithm:
FlowLayout
BorderLayout
GridLayout
For Windows and Frames, the default LayoutManager is
BorderLayout. For Panels, the default LayoutManager is
FlowLayout.

Flow Layout
The algorithm used by the FlowLayout is to lay out
Components like words on a page: Left to right, top to
bottom.
It fits as many Components into a given row before moving
to the next row.
aPanel.add(new Button("Add"));
aPanel.add(new Button("Delete"));

Border Layout
The BorderLayout Manager breaks the Container up into 5
regions (North, South, East, West, and Center).
When Components are added, their region is also
specified:
Frame aFrame = new Frame();
aFrame.add("North", new Button("Ok"));
aFrame.add("South", new Button("Add"));
aFrame.add("East", new Button("Delete"));
aFrame.add("West", new Button("Cancel"));
aFrame.add("Center", new Button("Recalculate"));

Border Layout (cont)
The regions of the BorderLayout are defined as follows:
Center
North
South
West East

Grid Layout
The GridLayout class divides the region into a grid of
equally sized rows and columns.
Components are added left-to-right, top-to-bottom.
The number of rows and columns is specified in the
constructor for the LayoutManager.
GridLayout theLayout = new GridLayout(2,2);
aPanel.setLayout(theLayout);
aPanel.add(new Button("Add"));
aPanel.add(new Button("Delete"));

What if I don’
t want a LayoutManager?
Ch. VIII - 20
LayoutManagers have proved to be difficult and frustrating
to deal with.
The LayoutManager can be removed from a Container by
invoking its setLayout method with a null parameter.
aPanel.setLayout(null);

Graphics
It is possible to draw lines and various shapes within a
Panel under the AWT.
Each Component contains a Graphics object which defines
a Graphics Context which can be obtained by a call to
getGraphics().
Common methods used in Graphics include:
drawLine
drawOval
drawPolygon
drawPolyLine
drawRect
drawRoundRect
drawString
draw3DRect
fill3DRect
fillArc
z
• fillOval
• fillPolygon
• fillRect
• fillRoundRect
• setColor
• setFont
• setPaintMode
•drawImage

AWT.pptx

More Related Content

Similar to AWT.pptx

Recently uploaded

AWT.pptx

Editor's Notes