Java Reference
In-Depth Information
Example 8−2: Command.java (continued)
/**
* This simple program demonstrates how a Command object can be parsed from
* a string and used as an ActionListener object in a Swing application.
**/
static class Test {
public static void main(String[] args) throws IOException {
javax.swing.JFrame f = new javax.swing.JFrame("Command Test");
javax.swing.JButton b1 = new javax.swing.JButton("Tick");
javax.swing.JButton b2 = new javax.swing.JButton("Tock");
javax.swing.JLabel label = new javax.swing.JLabel("Hello world");
java.awt.Container pane = f.getContentPane();
pane.add(b1, java.awt.BorderLayout.WEST);
pane.add(b2, java.awt.BorderLayout.EAST);
pane.add(label, java.awt.BorderLayout.NORTH);
b1.addActionListener(Command.parse(label, "setText(\"tick\");"));
b2.addActionListener(Command.parse(label, "setText(\"tock\");"));
f.pack();
f.show();
}
}
}
Exercises
8-1. Write a program that takes the name of a Java class as a command-line argu-
ment and uses the
Class
class to print out all the superclasses of that class.
For example, if invoked with the argument “java.awt.Applet”, the program
prints the following:
java.lang.Object java.awt.Component java.awt.Con-
tainer java.awt.Panel
.
8-2. Modify the program you wrote in Exercise 8-1 so that it prints out all inter-
faces implemented by a specified class or by any of its superclasses. Check
for the case of classes that implement interfaces that extend other interfaces.
For example, if a class implements
java.awt.LayoutManager2
, the
LayoutMan-
ager2
interface and
LayoutManager
, its superinterface, should be listed.
8-3. Define a class named
Assignment
that is modeled on the
Command
class shown
in Example 8-2. Instead of invoking a named method, as
Command
does,
Assignment
should assign a value to a named field of an object. Give your
class a constructor with the following signature:
public Assignment(Object target, Field field, Object value)
Also give it an
assign()
method that, when invoked, assigns the specified
value to the specified field of the specified object.
Assignment
should imple-
ment
ActionListener
and define an
actionPerformed()
method that also
performs the assignment. Write a static
parse()
method for
Assignment
that is
similar to the
parse()
method of
Command
. It should parse strings of the form
fieldname
=
value
and be able to parse boolean, numeric, and string values.
