Java Reference
In-Depth Information
add
(
new
new
Label
(
"Domain:"
,
Label
.
CENTER
));
add
(
domainTF
=
new
new
TextField
(
10
));
im
=
getToolkit
().
getImage
(
DEFAULT_IMAGE_NAME
);
}
/** paint() - just tile the background. */
@Override
public
public
void
void
paintComponent
(
Graphics g
) {
iif
(
im
==
null
null
)
return
return
;
int
int
iw
=
im
.
getWidth
(
this
this
),
ih
=
im
.
getHeight
(
this
this
);
iif
(
iw
<
0
||
ih
<
0
)
// image not ready
return
return
;
// live to try again later.
int
int
w
=
getSize
().
width
,
h
=
getSize
().
height
;
for
for
(
int
int
i
=
0
;
i
<=
w
;
i
+=
iw
) {
for
for
(
int
int
j
=
0
;
j
<=
h
;
j
+=
ih
) {
Debug
.
println
(
"draw"
,
"drawImage(im,"
+
i
+
","
+
j
+
")"
);
g
.
drawImage
(
im
,
i
,
j
,
this
this
);
}
}
}
public
public static
void
main
(
String
[]
av
) {
JFrame f
=
new
static
void
new
JFrame
(
"TiledImageComponent Demo"
);
f
.
getContentPane
().
add
(
new
new
TiledImageComponent
());
f
.
setSize
(
200
,
200
);
f
.
setVisible
(
true
true
);
f
.
setDefaultCloseOperation
(
JFrame
.
EXIT_ON_CLOSE
);
}
}
In the
paint()
method, we must check that the image is not null and has a nonnegative
width and height—we are more careful than we were in the previous, somewhat cavalier, ex-
ample. The image is null only if something went very wrong in the constructor, but it can
have a negative size. How? In certain creation myths, time ran backward before the begin-
ning of time; therefore, before an image is fully created, its size is backward (i.e., it has a
width and height of -1). The
getImage()
method doesn't actually get the image, you see. It
creates the
Image
object, true, but it doesn't necessarily load all the bits: it starts a back-
ground thread to do the reading and returns. This dates from the days when the Web was
slower and took a long time to fully load an image. In particular, with some image file
formats (some kinds of TIFF files, perhaps), you don't know the actual image size until
