©2004 Brooks/Cole Applets Graphics & GUIs. Figures ©2004 Brooks/Cole CS 119: Intro to JavaFall 2005 Graphical Programs Most applications these days are

©2004 Brooks/Cole

Applets

Graphics & GUIs

Figures ©2004 Brooks/ColeCS 119: Intro to Java Fall 2005

Graphical Programs

• Most applications these days are graphical

• The user controls what happens when by interacting with components like buttons and menus.

• Two types of graphical application in java– GUI application – Applet


Applets

• A Java applet is a program that is intended to transported over the Web and executed using a web browser

– An applet also can be executed using the appletviewer tool of the Java Software Development Kit

• An applet is embedded into an HTML file using a tag that references the bytecode file of the applet class

• The bytecode version of the program is transported across the web and executed by a Java interpreter that is part of the browser


The HTML applet Tag

<html> <head> <title>My Applet</title> </head>

<body> <applet code="Einstein.class" width=350 height=175> </applet> </body></html>


Applets

• The class that defines an applet extends the Applet class

– The class inherits all the behavior of the Applet class

– You can add whatever specific behavior you need for your applet

• An applet doesn't have a main method. Instead, there are several instance methods that serve specific purposes

– public void paint( Graphics g)

– public void init()


Graphics Class

• Frames and Applets have a graphics context associated with them.

• A Graphics object defines a graphics context on which we can draw shapes and text.

• The Graphics class is in the java.awt package.

• The state of a Graphics object includes such properties as height, width, foreground and background color and font.

• Positions within the Graphics context are measured from the upper left corner and they have units of pixels.


Graphics Methods


Drawing a Line

X

Y

10

20

150

45

g.drawLine (10, 20, 150, 45);

g.drawLine (150, 45, 10, 20);or


Drawing a Rectangle


Bounding Rectangles

• How do we specify the size of a shape that isn't rectangular?

• A bounding rectangle is the smallest rectangle that completely surrounds the shape.

• The java.awt.Dimension class can be used to create bounding rectangles that surround shapes. Dimension dim = new Dimension();

dim.width = 40;

dim.height = 70;


Drawing an Oval

X

Y

g.drawOval (175, 20, 50, 80);

175

20

50

80

boundingrectangle


Drawing an Arc

• An arc is a part of an oval

• To draw you need to specify– the bounding rectangle for the oval– the starting angle (measured from the x-axis in degrees– the angle the arc subtends


Drawing an Arc

g.drawArc (75, 20, 50, 80, 90, 90);


Drawing a String

• The drawString method can be used to display text in a Graphics context.void drawString( String text,

int x, int y;

• The position of the text relative to x and y is shown below


Color Class

• The java.awt.Color class allows us to designate the color of an object.

• The RGB scheme combines three values ranging from 0 to 255 for red, green, and blue.

Color pinkColor;pinkColor = new Color(255,175,175)


Color Class

• There are public class constants defined in the Color class for common colors:– Color.black

– Color.blue

– Color.green

– Color.magenta

– Color.orange


The Color Class

• Every drawing surface has a background color

g.setBackground(Color.white);

• Every graphics context has a current foreground color– The most recently set foreground color is what is

used for drawingg.setColor(Color.blue);g.drawRect(50, 50, 100, 30);


GUI Applications

• GUI applications usually start with a JFrame– Create a class that extends JFrame

• Each frame has a content pane which is where the GUI components go– Use a LayoutManager to control the

orgranization of components

• The frame also has a MenuBar


A Typical Swing-Based Containment Hierarchy


Control Flow in a GUI Application

• Components used to interact with the program generate Events

• Your program needs to listen for the events generated by the components– There are a number of different kinds of events– There are Listener interfaces for each type of

event


Figure 11.2: An Event “Triggers” the Initiation of an Event Object


Various Registration

Configurations

Documents

©2004 Brooks/Cole Applets Graphics & GUIs. Figures ©2004 Brooks/Cole CS 119: Intro to JavaFall 2005 Graphical Programs Most applications these days are