Errata

The code block on page 92 has these lines:

if (s == t) System.out.println("equal"); // But they are not equal!

and

if (a == b) System.out.println("equal"); // But they are not equal!

It is unclear how these lines execute, without running the code. Much better would be something like:

System.out.println(s == t); // Prints "false".

because now the reader doesn't have to compile the code to see the result.

The same thing can be said for the code block on page 93 using s.equals(t) (just state in the comment what it evaluates to, instead of leaving up the guesswork to the reader).

The description of the "decorator pattern" uses the example of an abstract class BurritoOptionalExtra which implements the Burrito interface.

The first sample code block defines the BurritoOptionalExtra class. This is followed by a note pointing out that it can only be used via subclasses. The second sample code block shows how said subclasses can be used. However, the subclasses themselves (Jalapeno and Guacamole) are never defined in the example.

While it is possible to extrapolate that Jalapeno and Guacamole are indeed subclasses of BurritoOptionalExtra, and the essentials of how they are implemented, it is unhelpful to leave this information out. Because the "decorator pattern" is actually being defined through the use of these examples (and not through descriptive text), the examples really need to be as complete as possible. Otherwise, the reader is forced to do double work: first to extrapolate the missing pieces of code, then to extrapolate the meaning of the "decorator pattern".

Providing this missing piece would improve the clarity of this section tremendously, at a cost of only a few extra lines.

Hi,
it seems that the given regex pattern "^#(\\w+)\\s*(\\w+)?" does not filter any symbols like !@#$%^&*()_+ as a meta.

Pattern SHELL_META_START = Pattern.compile("^#(\\w+)\\s*(\\w+)?");

I cannot get the Matcher to filter and separate characters from metas using the class below where the number 0 exits the programme.


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
*
* @author nicka
*/
public class ReadRegex {

public static void main(String[] args) {
Pattern SHELL_META_START = Pattern.compile("^#(\\w+)\\s*(\\w+)?");
try (BufferedReader console
= new BufferedReader(new InputStreamReader(System.in))) {
String line;
READ: while ((line = console.readLine()) != null && !"0".equals(line)) {
// Check for special commands ("metas")
Matcher m = SHELL_META_START.matcher(line);
if (m.find()) {
String metaName = m.group(1);
String arg = m.group(2);
//System.out.println("meta entered: " + metaName + " Text "+ arg);
doMeta(metaName, arg);
continue READ;
}
System.out.println("Text entered: "+line );
}
} catch (IOException e) {
// Handle FileNotFoundException, etc. here
e.printStackTrace();
}
}

public static void doMeta(String metaName, String arg) {
System.out.println("special commands: " + metaName);
System.out.println("Plain text: "+ arg);
}

}
Could you please offer a helping hand?
Thank you!
NA

In the example command:
"java some.package.MyClass java -jar my-packaged.jar"

What is the purpose of the word 'java' following '.MyClass' ?

(I am using the Google Books digital version.)
Thank You!

re: 14Jun2019 question about keyword, 'java' in java.exe command line exemplar: Sorry for the dumb question. Of coarse, 'java' is a stand-in for the name of the class holding the psvm() method to be called.