Question 1. What method defined by JComponent
paints the inside of a component?
Answer 1: As described in 14painting/conceptsHow
Swing Components Are Displayed, the http://java.sun/j2se/1.4.2/docs/api/javax/swing/JComponentpaintComponent(java.awt.Graphics)paintComponent
method paints a component's innards (with the exception of any children it
contains).
Question 2. Which of the following code snippets paint a rectangle (filled or not) that is 100x100 pixels?
a. g.fillRect(x, y, 100, 100)
b. g.fillRect(x, y, 99, 99)
c. g.drawRect(x, y, 100, 100)
d. b and c
e. a and c
Answer 2: a. As noted in 14painting/concepts2Introduction
to Painting Concepts, drawRect methods paint lines just below
the specified rectangle. So to get a 100x100 rectangle, you need to specify
a and of 99, 99 to drawRect. For fillXxx
methods, on the other hand, you specify exactly the desired and ,
so g.fillRect(x, y, 100, 100) results in a 100x100 rectangle.
Question 3. What code would you use to make
a component perform the next painting operation using the background color
at 50% transparency?
Answer 3: You can find the answer by looking
at the faded rocketship code in 14painting/practiceImplementing
a Custom Component and then modifying the specified amount of fading.
Here's the result:
Exercise 1. Using a standard border and custom component painting, implement a component that has a preferred size of 250x100, is opaque by , has a 5-pixel black border, and paints an &147;X&148; (using 5-pixel-thick lines) in the foreground color, as shown in the following figure. uiswing/QandE/ComponentDisplayer-1 260133ALIGNNATURALSIZEFLAG3ALTComponentDisplayer-1
Answer 1: See example-1dot4/XMarksTheSpot.javaXMarksTheSpot.java,
which you can run using example-1dot4/ComponentDisplayer.javaComponentDisplayer.java.
Here's the code that sets the border of the XMarksTheSpot component:
Here's the X-drawing code from the paintComponent method of XMarksTheSpot:
Exercise 2. Implement an icon that&146;s 10x10
pixels and paints a solid rectangle that fills the 10x10 area. If the icon&146;s
component is enabled, the rectangle should be red; if disabled, gray. Make
a copy of ButtonDemo.java that uses your custom Icon
for the middle button, instead of displaying middle.gif. The
following pictures show what the icon should look like.
Answer 2: See example-1dot4/SquareIcon.javaSquareIcon.java,
which you can run using this example-1dot4/ButtonDemo.javamodified ButtonDemo.java
Here's the code that sets the icon:
Icon middleButtonIcon = new SquareIcon(); ... b2 = new JButton("Middle button, middleButtonIcon);Here is SquareIcon's implementation of the three methods required
by the http://java.sun/j2se/1.4.2/docs/api/javax/swing/IconIcon
interface:
Exercise 3. Implement a border that paints a
red 15-pixel-tall stripe all the way across the top of its component. Test
this border by substituting it for the border on the component you created
in exercise 1. The result should look like the following figure.
uiswing/QandE/ComponentDisplayer-2 260133ALIGNNATURALSIZEFLAG3ALTComponentDisplayer-2
Answer 3: See example-1dot4/StripeBorder.javaStripeBorder.java,
which you can run using example-1dot4/ComponentDisplayer.javaComponentDisplayer.java
and example-1dot4/XMarksTheSpot.javaXMarksTheSpot.java (be sure
to uncomment the line that sets the border to StripeBorder). Here
is StripeBorder's implementation of the three methods required
by the http://java.sun/j2se/1.4.2/docs/api/javax/swing/border/BorderBorder
interface:
public void paintBorder(Component c, Graphics g,
int x, int y,
int , int ) {
g.setColor(Color.RED);
g.fillRect(x, y, c.get(), );
}
public Insets getBorderInsets(Component c) {
return new Insets(, 0, 0, 0);
}
public boolean isBorderOpaque() {
return true;
}
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