Ch 15 Aw t Components

8/12/2019 Ch 15 Aw t Components

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Objectives

The objectives of this chapter are:To discuss the classes present in the java.awt package

To understand the inheritance hierarchy of the AWT

To outline the basic structure of GUIs

To show how to add components to containersTo understand how to use Layout Managers

To understand basic graphics processing under the AWT


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AWT (Abstract Windowing Toolkit)

The AWT is roughly broken into three categories

Components

Layout Managers

Graphics

Many AWT components have been replaced by Swingcomponents

It is generally not considered a good idea to mix Swingcomponents and AWT components. Choose to use

one or the other.


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AWT Class Hierarchy

PanelButton

Checkbox

Choice

Label

List

Component

Container FrameWindow

TextArea

TextFieldTextComponent

Note: There are more classes, howeer,

these are what are coered in this chapter


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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 toComponent except it is the superclass for all GUI itemswhich can be displayed within a drop-down menu.

The Component class defines data and methods whichare relevant to all Components

setBoundssetSizesetLocation

setFontsetEnabledsetVisiblesetForeground -- coloursetBackground -- colour


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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 beplaced within a Container

The Container class defined all the data and methodsnecessary for managing groups of ComponentsaddgetComponentgetMaximumSize

getMinimumSizegetPreferredSizeremoveremoveAll


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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 aMenu Bar

! Frames are more commonly used than WindowsOnce defined, a Frame is a Container which can containComponents

Frame aFrame = new Frame(Hello World);aFrame.setSize(100,100);aFrame.setLocation(10,10);aFrame.setVisible(true);


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anels

When writing a GUI application, the GUI portion can

become quite complex.To manage the complexity, GUIs are broken down intogroups of components. Each group generally provides aunit of functionality.

A Panel is a rectangular Container whose sole purpose is

to hold and manage components within a GUI.

anel aanel = new anel();

aanel.add(new !utton("#$"));

aanel.add(new !utton("%ancel"));

Frame aFrame = new Frame("!utton &est");

aFrame.setSize(100,100);

aFrame.setLocation(10,10);

aFrame.add(aanel);


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!"ttons

This class represents a push-button which displays some

specified text.When a button is pressed, it notifies its Listeners. (Moreabout Listeners in the next chapter).

To be a Listener for a button, an object must implement theActionListener Interface.


!utton o$!utton = new !utton("#$");

!utton cancel!utton = new !utton("%ancel");

aanel.add(o$!utton));aanel.add(cancel!utton));

o$!utton.add'ctionListener(controller);

cancel!utton.add'ctionListener(controller1);


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#abels

This class is a Component which displays a single line of

text.Labels are read-only. That is, the user cannot click on alabel to edit the text it displays.

Text can be aligned within the label

Label aLabel = new Label("nter *assword+");

aLabel.set'linment(Label.-/H&);

aanel.add(aLabel);


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#ist

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

selectedList aList = new List();aList.add("%alar");aList.add("dmonton");aList.add("-eina");aList.add("Vancouer");

aList.set2ulti*le2ode(true);


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Checkbo$

This class represents a GUI checkbox with a textual label.

The Checkbox maintains a boolean state indicating whetherit is checked or not.

If a Checkbox is added to a CheckBoxGroup, it will behavelike a radio button.

%3ec$bo4 cream%3ec$bo4 = new %3ec$!o4("%ream");

%3ec$bo4 suar%3ec$bo4 = new %3ec$!o4("Suar");

56

i7 (cream%3ec$bo4.etState())

8

co77ee.add%ream();

9


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Choice

This class represents a dropdown list of Strings.

Similar to a list in terms of functionality, but displayeddifferently.

Only one item from the list can be selected at one time andthe currently selected element is displayed.

%3oice a%3oice = new %3oice();

a%3oice.add("%alar");

a%3oice.add("dmonton");

a%3oice.add("'lert !a");

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Strin selected:estination= a%3oice.etSelectedtem();


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Te$tField

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 theAWT

TextField emailTextField = new TextField();

TextField passwordTextField = new TextField();

passwordTextField.setEchoChar("*");

[]

String userEmail = emailTextField.getText();

String userpassword = passwordTextField.getText();


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Te$tArea

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()

< rows, 0 columns

&e4t'rea 7ull'ddress&e4t'rea = new &e4t'rea(


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#ayo"t %anagers

Since the Component class defines the setSize() and

setLocation() methods, all Components can be sized andpositioned with those methods.

Problem: the parameters provided to those methods aredefined in terms of pixels. Pixel sizes may be different

(depending on the platform) so the use of those methodstends to produce GUIs which will not display properly onall platforms.

Solution: Layout Managers. Layout managers are

assigned to Containers. When a Component is added toa Container, its Layout Manager is consulted in order todetermine the size and placement of the Component.

NOTE: If you use a Layout Manager, you can no longerchange the size and location of a Component through the

setSize and setLocation methods.


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#ayo"t %anagers (cont)

There are several different LayoutManagers, each of whichsizes and positions its Components based on an algorithm:

FlowLayout

BorderLayout

GridLayout

For Windows and Frames, the default LayoutManager isBorderLayout. For Panels, the default LayoutManager isFlowLayout.


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Flow #ayo"t

The algorithm used by the FlowLayout is to lay outComponents like words on a page: Left to right, top tobottom.

It fits as many Components into a given row before movingto the next row.



aanel.add(new !utton("'dd"));

aanel.add(new !utton(":elete"));aanel.add(new !utton("%ancel"));


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!order #ayo"t

The BorderLayout Manager breaks the Container up into 5regions (North, South, East, West, and Center).

When Components are added, their region is alsospecified:

Frame aFrame = new Frame();

aFrame.add(">ort3", new !utton("#$"));

aFrame.add("Sout3", new !utton("'dd"));

aFrame.add("ast", new !utton(":elete"));

aFrame.add("West", new !utton("%ancel"));

aFrame.add("%enter", new !utton("-ecalculate"));


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!order #ayo"t (cont)

The regions of the BorderLayout are defined as follows:

%enter

>ort3

Sout3

West ast


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&rid #ayo"t

The GridLayout class divides the region into a grid ofequally 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.


/ridLaout t3eLaout = new /ridLaout(,);

aanel.setLaout(t3eLaout);


aanel.add(new !utton("'dd"));

aanel.add(new !utton(":elete"));

aanel.add(new !utton("%ancel"));


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What i' dont want a #ayo"t%anager

Ch. VIII - 21

LayoutManagers have proved to be difficult and frustratingto deal with.

The LayoutManager can be removed from a Container byinvoking its setLayout method with a null parameter.


aanel.setLaout(null);


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Ch 15 Aw t Components

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