Java Reference
In-Depth Information
•
HTML forms are a common mechanism to input user-specified data into a
JSP application.
•
Java code is added to a JSP page through
directive
,
expression
,
declaration
, and
scriptlet
tags.
Answers to Self-Test Exercises
1. The invocation of
Thread.sleep
takes place inside a thread. Every action in Java
takes place inside some thread. Any action performed by a method invocation in
a specific thread takes place in that thread. Even if it does not know where it is,
a method's action takes place where the method invocation is; if you are lost and
yell out, you might not know where you are but the yell would still be wherever it
is you are.
2. The class
Packer
inherits the method
start
from the base class
Thread
and is
not overridden. The method
start
invokes the method
run
, but when
start
is
invoked by an object of the class
Packer
, it is the definition of
run
that is given in
the class
Packer
that is used, not the definition of
run
given in the definition of
Thread
. That is exactly what is meant by
late binding
or
polymorphism
.
3. In this program, the code that runs in each thread is fairly short. As a result, there
is a good chance that each thread runs to completion before the next thread begins.
The
sleep
method forces a thread to suspend and another thread to begin. This
increases the likelihood that there will be contention for the shared variable and a
race condition.
4. The code synchronizes access to the shared variable but the
main
method does not
wait for all threads to finish before printing out the value of the shared variable.
Thus, it is possible that
main
will output a premature value of
counter
if
main
completes before any one of the threads that it creates. To correct this problem,
invoke the
join()
method on each thread before outputting counter as illustrated
in Display 19.5 .
5. A port is used to identify which program should receive data from the network.
One program only may be bound to a specific port.
6. Each client connection may run in its own thread, requiring a large amount of
memory, disk space, or processor time.
7 .
Persistence
means that a component's state can be saved so that the next time it is
used it remembers what state it was in.
8. The same one that is used for Swing and AWT.
9.
SELECT Result.Title, Names.Author, Result.Author_ID
FROM Result, Names
WHERE Result.Author_ID = Names.Author_ID
10. A connection string is used to connect to (and possibly create) a database via
JDBC. The protocol, database name, and other parameters (such as the username,
password, or flag to create a new database) are specified in the connection string.
11. The
execute
method can be used to execute any SQL statement, but it is generally
used for SQL commands where return values are not needed. It returns a Boolean
