Swing I - Absolute Java - page 959

Color
You can set the color of a JFrame (or other GUI object). To set the background color
of a JFrame , use
getContentPane().setBackground( Color );
For example, the following will set the color of the JFrame named someFrame to blue:

getContent
Pane
set
Background

someFrame.getContentPane().setBackground(Color.BLUE);
Alternatively, if you set the color in the constructor for the JFrame , the invocation
takes the form

Color.BLUE

getContentPane().setBackground(Color.BLUE);
which is equivalent to

this .getContentPane().setBackground(Color.BLUE);
The next Programming Example, “A GUI with a Label and Color,” shows a JFrame
object (in fact, two of them) with color.
The method invocation getContentPane() returns something called the content
pane of the JFrame . So,

content pane

getContentPane().setBackground(Color.BLUE);
actually sets the color of the content pane to blue. The content pane is the “inside” of
the JFrame , so coloring the content pane has the effect of coloring the inside of the
JFrame . However, you can think of
getContentPane().setBackground( Color );
as a peculiarly spelled method invocation that sets the color of the JFrame . (In this
book, we will not be referring to the content pane of a JFrame except when we want to
color the JFrame , so we will explain the content pane no further.)
Use getContentPane only when you give color to a JFrame . As you will see, to set
the color of some component in a JFrame , such as a button, simply use the method
setBackground with the button or other component as the calling object. You will see
examples of adding color to components in Section 17.3.
What kind of thing is a color when used in a Java Swing class? Like everything
else in Java, a color is an object—in this case, an object that is an instance of the class
Color . The class Color is in the java.awt package. (Note that the package name is
java.awt , not javax.awt . )
In a later chapter, you will see how you can define your own colors, but for now
we will use the colors that are already defined for you, such as Color.BLUE , which
is a constant named BLUE that is defined in the class Color . The constant, of course,
represents the color blue. If you set the background of a JFrame to Color.BLUE , then
the JFrame will have a blue background. The type of the constant Color.BLUE and
other such constants is Color . The list of color constants that are defined for you are
given in Display 17.5. The next Programming Example, “A GUI with a Label and
Color,” has an example of a constructor with one parameter of type Color .

get
Content
Pane

color

Color