Object-Oriented Concepts - SCJP Sun Certified Programmer for Java Platform SE6 - page 399

The compiler error generated is
Square.java:4: modifier abstract not allowed here
public abstract Square(int s) {
^
1 error
A constructor cannot be abstract because it cannot be overridden. You can specify that
a method cannot be overridden as well using the final modifi er, discussed in the next
section.
The final Modifier
The fi nal modifi er is applied to local variables, fi elds, methods, or classes. The properties of
the final modifi er are
A final variable or field cannot be changed. These are referred to as constants .
A final method cannot be overridden. (We discussed final methods in Chapter 2.)
A final class cannot be subclassed.
A final variable or fi eld cannot be changed once it is assigned. The following MyLogger
class contains a final fi eld, a final parameter, and a final local variable:
1. import java.io.File;
2.
3. public final class MyLogger {
4. private final File DEST;
5.
6. public MyLogger(File d) {
7. DEST = d;
8. }
9.
10. public void logMessage(final String MESSAGE) {
11. final long TIME = new java.util.Date().getTime();
12. //write time and message to file...
13. }
14. }
The fi eld DEST on line 4 and the parameter MESSAGE on line 10 are referred to as blank
fi nals . They are constants that do not have an initial value, and once they are assigned a
value, they cannot be changed. The TIME variable on line 11 is assigned the current time
and cannot be changed.