Java Reference
In-Depth Information
height
. The last two arguments,
arcWidth
and
arcHeight
, specify the arcs that will be
used for the corners so as to produce a rounded rectangle. Each corner is replaced with
a quarter of an oval that is
arcWidth
pixels wide and
arcHeight
pixels high. This is
illustrated in Display 18.15. To obtain corners that are arcs of circles just make
arcWidth
and
arcHeight
equal.
paintComponent
for Panels
You can draw figures on a
JPanel
and place the
JPanel
in a
JFrame
. When defining a
JPanel
class that contains a graphics drawing, you use the method
paintComponent
instead of the method
paint
, but otherwise the details are similar to what we have seen
for
JFrame
s.
JFrame
s use the method
paint
. However,
JPanels
—and in fact all
JComponents
—use the method
paintComponent
. A very simple example of using
paintComponent
with a
JPanel
is given in Display 18.16.
If you look back at Display 17.12 in Chapter 17, you will see that a
JPanel
is a
JComponent
, but a
JFrame
is not a
JComponent
. A
JFrame
is only a
Component
. That is
why they use different methods to paint the screen.
Action Drawings and
repaint
The program in Display 18.17 is similar to the program in Display 18.13. It draws a
happy face similar to the happy face given in Display 18.13, but with one difference:
There is a button at the bottom of the GUI that says
Click
for
a
Wink
. When you
click that button, the left eye winks. (Remember the left eye is on your right.) Let's see
the details.
Display 18.15
A Rounded Rectangle
g.drawRoundRect(x, y, width, height, arcWidth, arcHeight);
produces:
width
(
x
,
y)
arcWidth
height
arcHeight
