Topics • Applet Structure Chapter 4 • Executing an Applet • Drawing Shapes with Graphics Methods ���������������� • Using Colors �������������������� Applets Applet Structure • Executed by a browser or applet viewer • Do not use main method • Two methods called automatically: 1. init method • Opens a window, as well as the Java console • Browser calls init when applet starts • Use to initialize variables and objects 2. paint method • Applet viewer comes with Java Software • Browser calls after init and whenever Development Kit (SDK) window needs to be redrawn • Use to draw to screen • See Example 4.01 ShellApplet.java Executing an Applet <Applet> Tag <APPLET> • A Web page tells the browser to run the CODE = Classname.class applet CODEBASE = ‘.’ directory of class file • HTML tags come in pairs, data goes WIDTH = nnn width of window in pixels between start and end tags HEIGHT = nnn height of window in pixels </APPLET> <HTML> </HTML> start and end of HTML code <HEAD> </HEAD> start and end of header <TITLE> </TITLE> text to display in title bar <BODY> </BODY> start and end of page content 1
Minimal HTML File HTML File for FirstApplet <HTML> <HTML> <HEAD> <HEAD> <TITLE>TitleName</TITLE> <TITLE>My First Applet</TITLE> </HEAD> </HEAD> <BODY> <BODY> <APPLET CODE="ClassName.class" <APPLET CODE="FirstApplet.class" CODEBASE=. CODEBASE=. WIDTH=nnn WIDTH=400 HEIGHT=nnn> HEIGHT=300> </APPLET> </APPLET> </BODY> </BODY> </HTML> </HTML> Executing an Applet The Graphics Class • If HTML file is named FirstApplet.html , • Browser or appletviewer sends a Graphics you can execute the applet using this object to the paint method command: • The Graphics object represents the applet appletviewer FirstApplet.html window, current font, and current color • Many IDEs automatically create and launch the • Provides methods to draw shapes and text HTML file for running an applet on the window The Graphics Coordinate System Graphics Class Methods • Methods are available for drawing lines, rectangles, ovals, and other shapes, and for setting the current color • All methods have a void return type, so method calls are standalone statements • draw… methods draw an outlined shape • fill… methods draw a solid shape 2
Displaying Text Drawing a Line Return Method name and argument list Return Method name and argument list type type void drawLine( int xStart, int yStart, void drawString ( String s, int x, int y ) int xEnd, int yEnd ) displays the String s. The ( x, y ) coordinate is draws a line starting at ( xStart, yStart ) and lower-left corner of first letter. ending at ( xEnd, yEnd ) • Example: g.drawLine( xStart, yStart, xEnd, yEnd ); g.drawString( "Hello", x, y ); • See Example 4.5 LineDrawingApplet.java • See Example 4.4 DrawingTextApplet.java Drawing A Rectangle Drawing A Solid Rectangle Return Method name and argument list Return Method name and argument list type type void drawRect( int x, int y, void fillRect( int x, int y, int width, int height ) int width, int height ) draws an outlined rectangle with ( x,y ) as draws a solid rectangle in the current the upper-left corner and the width and color with ( x,y ) as the upper-left corner and height specified the width and height specified g.drawRect( x, y, width, height ); g.fillRect( x, y, width, height ); Drawing An Oval Drawing A Solid Oval Return Method name and argument list Return Method name and argument list type type void drawOval( int x, int y, void fillOval( int x, int y, int width, int height ) int width, int height ) draws an outlined oval within an draws a solid oval in the current color invisible bounding rectangle. inside an invisible bounding rectangle g.drawOval( x, y, width, height ); g.fillOval( x, y, width, height ); 3
Drawing Squares and Circles • To draw a square, use drawRect or fillRect • When drawing a figure using Graphics with equal values for width and height . methods, specify coordinate values as offsets from a starting (x,y) coordinate. • To draw a circle, use drawOval or fillOval with equal values for width and height • This will make your figure easier to move or resize. • See Example 4.4 ShapeDrawingApplet.java • See Example 4.7 Astronaut.java Using Color Setting the Current Color • The Graphics context has a current Return Method name and argument list value foreground color void setColor( Color c) • All drawing is done in current color; the sets the current color to the Color c current color is in effect until changed • The default color is black. Example: • To use color, import the Color class from g.setColor( Color.RED ); the java.awt package static Color Constants Custom Colors • Colors consist of red , green , and blue Color.BLACK Color.GRAY components (RGB). Color.WHITE Color.ORANGE • Color constructor: Color.RED Color.YELLOW Color( int rr, int gg, int bb ) Color.GREEN Color.PINK creates a color consisting of the red ( rr ), green ( gg ), and blue ( bb ) values specified. rr , gg , and Color.BLUE Color.MAGENTA bb must be between 0 and 255 Color.CYAN • Example: Color.LIGHT_GRAY Color green = new Color( 0, 255, 0 ); Color.DARK_GRAY • See Example 4.8 AstronautWithColor.java 4
Homework1 • Solve the following Problems: • Number 31 Page 31 • Number 35 Page 203 5
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