Displaying a drawing - An Introduction to Graphical User Interfaces with Java Swing - page 49

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Figure 5.1 The effect of the commands drawLine(10,20,30,10) , drawRect(40,25,
20,10) and drawOval(80,40,10,20). The dotted lines and the dimensions do not ap-
pear in the graphic. The bounding rectangle for the oval is shown as a dotted line

drawString(text,xleft,ybottom) draws the string text . The lower left corner
of the bounding rectangle of the text is at ( xleft, ybottom ). This is the reference
point .

fillRect draws a filled rectangle using the current colour, otherwise like
drawRect .
fillOval draws a filled ellipse using the current colour, otherwise like drawOval .
setColor(col) sets the colour of the drawing to col . This colour is used until the
setColor command is used again.

■ 5.3 A simple graphical application

Our application is only to demonstrate the use of the graphic commands inside
paintComponent .Asthere is no user interaction that changes the drawing,
we do not need a model or control part. In the example we derive a class
SimpleGraphicsPanel from JPanel .Inthe constructor we set the background
to white (it is normally grey) and set the size to 300 300 pixels. Then method

paintComponent is overridden. As explained above, we first make a call to the
original paintComponent method. Then follow a number of graphics commands
which set the drawing colour and draw various shapes and a string. The com-
mands are provided by the Graphics class of AWT and thus have the syntax
g.drawSomething where g is an instance of Graphics . Now whenever the panel
is redrawn these commands are executed and the graphical objects are displayed.
Note that drawing a filled object with the background colour makes parts of other
objects 'disappear'. In the example a white oval partly covers a cyan coloured
one.

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