Java Reference
In-Depth Information
As shown in Fig. 17.3, an instance of class JButton is a component that can be
placed in a JFrame . The creation of a new JButton is easy; the argument of the
constructor in a new-expression is the string to be displayed on the button, e.g.:
A footnote on
top of lesson
page 17.2 gives
more detail.
new JButton("Yeeaaah")
JButton is a subclass of the older class Button of package java.awt , and
you can create Buttons as well:
Get a class that
creates buttons
from a footnote
on 17.2.
new Button("Nyaaaah")
and place them in the content pane of the JFrame .
A JButton and a Button look slightly different, as you can see in a foot-
note near the top of lesson page 17.2.
JLabels, JTextFields, JTextAreas
Putting labels into a JFrame
An instance of class JLabel is a component that is a short text, an image, or
both. In this text, we deal only with JLabel s that are text. As you know from Sec.
17.1, the argument of a JLabel constructor is the text that is to be displayed.
Here is an example:
Activity 17-2.2
Get a class that
creates labels
from a footnote.
JLabel label= new JLabel("top label");
If a window is resized by dragging, as activity 17.2.2 shows, a label may be
partially obscured. Of course, you can drag to make the window bigger.
Retrieve and change the text in a label using getText and setText , e.g.
String s= label.getText();
label.setText("new text");
Labels are left-adjusted by default, but you can center or right-adjust them.
For example, use this call to right-adjust the label:
The constants of class SwingConstants that can be used as the argument
Change the vertical alignment using a call like the following. Possible argu-
ments are these constants of SwingConstants : TOP , CENTER , and BOTTOM .
Putting text fields into a JFrame
An instance of class JTextField is a component that is a one-line field into
which the user can type text. It is often called simply a text field . An example of
a JTextField appears in the north part of the content pane of Fig. 17.2.
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