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5.6 Implementing the Graphical User Interface
Without learning about graphical user interface GUI APIs, you would still be able to create quite a descent range of different programs. However, your applications are very
likely to be bland and unappealing to the users. Having a good GUI affects the usage of your application. This results in ease of use and enjoyment of use for the users of your
program. Java provides tools like Abstract Windowing Toolkit AWT and Swing to develop interactive GUI applications. The following section provides a discussion on the
Abstract Windowing Toolkit and Swing
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. The Java Foundation Classes JFCs, which is an important part of the Java SDK, refers to
a collection of APIs that simplifies the development Java GUI applications. It primarily consists of five APIs including AWT and Swing. The three other APIs are Java2D,
Accessibility, and Drag and Drop. All these APIs assist developers in designing and implementing visually-enhanced applications.
Both AWT and Swing provides GUI components that can be used in creating Java applications and applets. You will learn about applets in a latter section. Unlike some AWT
components that use native code, Swing is written entirely using the Java programming language. As a result, Swing provides a platform-independent implementation ensuring
that applications deployed across different platforms have the same appearance. AWT, however, does ensure that the look and feel of an application run on two different
machines be comparable. The Swing API is built around a number of APIs that implement various parts of the AWT. As a result, AWT components can still be used with Swing
components.
5.6.1 AWT GUI Components
Fundamental Window Classes
In developing GUI applications, the GUI components such as buttons or text fields are placed in containers. These are the list of important container classes provided in the
AWT.
8 The use of the text verbatim from the JEDI Introduction to Programming II Course has prior approval from their authors.
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AWT Class Description
Component An abstract class for objects that can be displayed on the console and
interact with the user. The root of all other AWT classes. Container
An abstract subclass of the Component class. A component that can contain other components.
Panel Extends the Container class. A frame or window without the titlebar, the
menubar nor the border. Superclass of the Applet class. Window
Also extends Container class. A top-level window, which means that it cannot be contained in any other object. Has no borders and no menubar.
Frame Extends the Window class. A window with a title, menubar, border, and
resizing corners. Has four constructors, two of which have the following signatures:
Frame FrameString title
Table 1.2.1: AWT Container classes
To set the size of the window, the overloaded setSize method is used. void setSizeint width, int height
Resizes this component to the width and height provided as parameters. void setSizeDimension d
Resizes this component to d.width and d.height based on the Dimension d specified. A window by default is not visible unless you set its visibility to true. Here is the syntax
for the setVisible method. void setVisibleboolean b
In designing GUI applications, Frame objects are usually used. Heres an example of how to create such an application.
import java.awt.; public class SampleFrame extends Frame {
public static void mainString args[] { SampleFrame sf = new SampleFrame;
sf.setSize100, 100; Try removing this line
sf.setVisibletrue; Try removing this line
} }
Note that the close button of the frame doesnt work yet because no event handling mechanism has been added to the program yet. Youll learn about event handling in the
next module.
Graphics
Several graphics method are found in the Graphics class. Here is the list of some of these methods.
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drawLine drawPolyline
setColor fillRect
drawPolygon getFont
drawRect fillPolygon
setFont clearRect
getColor drawString
Table 1.2.2a: Some methods of class Graphics
Related to this class is the Color class, which has three constructors.
Constructor Format Description
Colorint r, int g, int b Integer value is from 0 to 255.
Colorfloat r, float g, float b Float value is from 0.0 to 1.0. Colorint rgbValue
Value range from 0 to 2
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-1 black to white. Red: bits 16-23
Green: bits 8-15 Blue: bits 0-7
Table 1.2.2b: Color constructors
Here is a sample program that uses some of the methods in the Graphics class. import java.awt.;
public class GraphicPanel extends Panel { GraphicPanel {
setBackgroundColor.black; constant in Color class
} public void paintGraphics g {
g.setColornew Color0,255,0; green
g.setFontnew FontHelvetica,Font.PLAIN,16; g.drawStringHello GUI World, 30, 100;
g.setColornew Color1.0f,0,0; red
g.fillRect30, 100, 150, 10; }
public static void mainString args[] { Frame f = new FrameTesting Graphics Panel;
GraphicPanel gp = new GraphicPanel; f.addgp;
f.setSize600, 300; f.setVisibletrue;
} }
For a panel to become visible, it should be placed inside a visible window like a frame.
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More AWT Components
Here is a list of AWT controls. Controls are components such as buttons or text fields that allow the user to interact with a GUI application. These are all subclasses of the
Component class.
Label Button
Choice TextField
Checkbox List
TextArea CheckboxGroup
Scrollbar
Table 1.2.3: AWT Components
The following program creates a frame with controls contained in it. import java.awt.;
class FrameWControls extends Frame { public static void mainString args[] {
FrameWControls fwc = new FrameWControls; fwc.setLayoutnew FlowLayout; more on this later
fwc.setSize600, 600; fwc.addnew ButtonTest Me;
fwc.addnew LabelLabe; fwc.addnew TextField;
CheckboxGroup cbg = new CheckboxGroup; fwc.addnew Checkboxchk1, cbg, true;
fwc.addnew Checkboxchk2, cbg, false; fwc.addnew Checkboxchk3, cbg, false;
List list = new List3, false; list.addMTV;
list.addV; fwc.addlist;
Choice chooser = new Choice; chooser.addAvril;
chooser.addMonica; chooser.addBritney;
fwc.addchooser; fwc.addnew Scrollbar;
fwc.setVisibletrue; }
}
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5.6.2 Layout Managers
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