Missing "import javax.swing.*;" before "import java.awt.*;". If you place the HelloComponent in its own file the java compiler will not find JComponent as it is not in the java.awt name space.

HelloComonent hello = new HelloComponent();
frame.add( hello );

should be:

frame.getContentPane().add( new HelloComponent() );

--------------

This is a correction to the current errata for this page.
The current errata suggests frame.add(new HelloComponent() );
which results in a run-time error, e.g.:

Exception in thread "main" java.lang.Error: Do not use javax.swing.JFrame.add() use javax.swing.JFrame.getContentPane().add() instead
at javax.swing.JFrame.createRootPaneException(JFrame.java:465)
at javax.swing.JFrame.addImpl(JFrame.java:491)
at java.awt.Container.add(Container.java:307)
at HelloJava.main(HelloJava.java:19)

For

java version "1.4.2-02"
Java(TM) 2 Runtime Environment, Standard Edition (build Blackdown-1.4.2-02)
Java HotSpot(TM) Client VM (build Blackdown-1.4.2-02, mixed mode)

The "HelloJava1" class in the diagram should be "HelloComponent." This is because in
the example code, HelloJava1 never inherits from JComponent, HelloComponent does.

HelloJava1 is shown. This should be HelloComponent.

frame.add( new HelloComponent2("Hello, Java!") );

should be:

frame.getContentPane().add( new HelloComponent2("Hello, Java!") );

(The equivalent line is correct on page 42)

Likewise

HelloComponent2 newObject = new HelloComponent2("Hello, Java!");
frame.add( newObject );

should be:

HelloComponent2 newObject = new HelloComponent2("Hello, Java!");
frame.getContentPane().add( newObject );

(probably worth checking for s/frame.add/frame.getContentPane().add/g thoughout)

Extracted code refers to "frame.add" when actual code on page 42 is
frame.getContentPane().add...

The text shows three examples of using the jar utility:

% jar xvf spaceblaster.jar
% jar xvf spaceblaster.jar filename
% jar tvf spaceblaster.jar

None of these examples actually work in practice, because the jar option list needs
to be prefixed with a "-". For example, the correct version of the first command
line would be:

% jar -xvf spaceblaster.jar

The code snippet involves creating a socket with the IP address: 207.46.131.13. When
I tried the example it failed to connect; in fact, I couldn't even ping that address.
Consider using a URL that's more likely to be always-on (e.g., www.google.com). I
tried www.google.com instead and it worked.

The last sentence ends with "as does a method with a conditional that the compiler
can tell will NEVER be fulfilled:" (emphasis mine)

It then shows the code snippet:

if (1 < 2)
return;
// unreachable statements

The problem with this sentence is that the condional will ALWAYS be fulfilled,
because it will always be true that the integer constant 1 is less than the integer
constant 2.

The number 1 is not a prime. At least according to all the number theory books I
have read.

The last sentence in the paragraph says "In either case, if you don't initialize a
variable when you declare it, it's given a default value appropriate for its type
(null, zero, or false)."

"zero" is typeset in constant width font. According to the book preface, in the
"Conventions Used in This Book" section, constant width is for:
- anything that might appear in a Java program
- tags in HTML or XML
- keywords, objects and environment variables

I don't believe the author's intent is to say there is a Java keyword "zero", or a
constant named "zero", or an object with the name "zero", etc., which some variables
are initialized to. Instead, I believe they just mean the numeric value zero: "0".

Consider changing "zero" to "0", or eliminating the constant width font and using
regular font for "zero", so as to avoid implying that the string "zero" has special
significance in Java code.

The problematic sentence reads:

"This means that if you change a static final variable, you may have to recompile
all code that uses that class (this is really the only case where you have to do
that in Java)."

The parenthetical seems wrong. What if you change the name of a method--isn't it
possible that you would have to recompile all clients, if they were callers of that
method? Or what if you changed the type of a public member variable? Couldn't that
also require a recompile of all clients--if all the clients relied on it?

The parenthetical is at best ambiguous and at worst false.

The table contains two columns: one for primitive types and one for wrapper classes.
The names for primitive types are capitalized. This is a mistake because Java primitive
type names are case sensitive, and always begin with a lower-case letter.

The text explains an enum's compareTo() method as returning an integer greater
than zero when the target enum is greater than the reference enum (in the enum ordering).

Then the authors present the code snippet:

Level level = Level.HIGH;
Level anotherLevel = Level.LOW;
if (level.compareTo( anotherLevel ) > 0 ) // true
doSomething();

The "true" comment would lead one to believe that compareTo() returns an integer
greater than zero in this case. Since anotherLevel is the target enum, and level
is the reference enum, this implies that Level.LOW is greater than Level.HIGH
in the enum order.

It seems odd that LOW would be higher than HIGH, until one realizes that this
condition could be true, given the (counter-intuitive) enum order: { HIGH, ..., LOW }.
But since we aren't told in the example what the actual enum order is, it's not
possible to determine whether the "// true" comment is in fact accurate.

It would be helpful in this case to either include the enum declaration, provide
more detail in the text, or perhaps switch the places of the Level.HIGH and Level.LOW
tokens in the code.

The text reads:

"The java.io.Serializeable interface is a good example. Classes that implement
Serialize don't have to add any methods or variables."

The problem is the text first calls this interface Serializeable, but then calls
it Serialize. The correct name is Serializeable.

This line:

object[0] = new Date(); // Runtime ArrayStoreException!

Should read:

objects[0] = new Date(); // Runtime ArrayStoreException!

In the last code example, in the try block, the code should read
"new ExceptionTester<ClassNotFoundException>().test(new ClassNotFoundException());"
rather than
"new E<ClassNotFoundException>().test(new ClassNotFoundException());".

In the while loop of the getMessage() method, you call a notify(). This is probably useless. Notify can only wake up the producer as getMessage() is only called by the consumer.

The producer goes to wait when the queue has more than five messages. The condition to enter the while loop is an empty queue. Both conditions are never met together.

Is:
The second value (60) is a convention used to support leap years.

Should be:
The second value (60) is a convention used to support leap seconds.



For confirmation, go to:
iers.org
Search the web site for leap seconds,
Follow the IERS Glossary: Leap Seconds link
Click on the related link for Leap Seconds
And click on "here" in the "historical list of leap seconds can be found here" which will take you to
http://maia.usno.navy.mil/ser7/tai-utc.dat
The historical list shows many leap seconds (including eight of the last ten) that did not occur during Leap Years.

The code sample's first line declares a collection of Date objects, named "col", but the for loop in the second line iterates over the contents of "collection", not "col".

The loop should iterate over "col", as in this revised version:

Collection<Date> col = ...
for( Date date : col )
System.out.println( date );

In the for loop header "collection" should be "col".

The line
WorkRequest request , WorkListener listener)
should read
final WorkRequest request , final WorkListener listener)

The example code given on this site is correct, but the book leaves out both instances of the word "final".