Mistake in GuideBook for SCJP Java 6.0, Chapter 10, Self Test question 11

[Tomasz Sadura]

Given the following directory structure:

test-|
     |- GetJar.java
     |
     |- myApp-|
              |-Foo.java

And given the contents of GetJar.java and Foo.java:

3. public class GetJar {
4.   public static void main(String[] args) {
5.     System.out.println(myApp.Foo.d);
6.   }
7. }

3. package myApp;
4. public class Foo { public static int d = 8; }

If the current directory is "test", and myApp/Foo.class is placed in a JAR file called MyJar.jar
located in test, which set(s) of commands will compile GetJar.java and produce the output 8?
(Choose all that apply.)

A. javac -classpath MyJar.jar GetJar.java
   java GetJar

B. javac MyJar.jar GetJar.java
   java GetJar

C. javac -classpath MyJar.jar GetJar.java
   java -classpath MyJar.jar GetJar

D. javac MyJar.jar GetJar.java
   java -classpath MyJar.jar GetJar

Answer:
A is correct. Given the current directory and where the necessary files are located, these
are the correct command line statements.

B and D are wrong because javac MyJar.jar GetJar.java is incorrect syntax. C is wrong
because the -classpath MyJar.java in the java invocation does not include the test directory.
(Objective 7.5)

The A answer is not correct, because the Foo class cannot be found when executing the GetJar. None of the answers is correct.

[Ankit Garg]

Hi Tomasz, welcome to javaranch.

This error has been noticed before and has been reported here. You can submit any other error that you find in the book in that topic created by Bert Bates...

[Justin Fleming]

I'm having trouble with this one too.

The other thread linked above says "GetJar refers to "Foo.d" but does not either import myApp.* or refer to Foo.d by its fully qualified name. There is no way to get this code to compile." That is not the case in my book, or in the OP's (Original Poster). My book also has the following which uses the fully qualified name.

3. public class GetJar {
4. public static void main(String[] args) {
5. System.out.println(myApp.Foo.d);
6. }
7. }    

Furthermore, option "A" compiles the code fine on my machine, so long as the directory structure is preserved in the Jar file.

The jar can be created with after compiling the the java file using
javac -classpath MyJar.jar GetJar.java
jar -cf myJar.jar myApp/Foo.class


However my issue is that the explanation for option C seems incorrect.

  B and D are wrong because javac MyJar.jar GetJar.java is incorrect syntax. C is wrong
because the -classpath MyJar.java in the java invocation does not include the test directory.
(Objective 7.5)  

1st) there is no "MyJar.java" in option C. It should be "MyJar.jar"
2nd) even if it was written correctly I would take this to mean

java -classpath test/Myjar.jar GetJar

which is not the reason it would not work.

3rd) I think what it is trying to say is that the Jar file (MyJar.jar) does not include the GetJar.class file (which is in the test directory).

A jar that contains this file can be created using the following command. This will allow option C to run and be correct as well. But it was not specifically said that these files were or were not in the Jar file.

jar -cf MyJar.jar GetJar.class myApp/Foo.class

or

jar -cf MyJar.jar *

So really C could also be correct, unless we assume that the only class in the Jar is myApp/Foo.class
perhaps giving the jar file creation command (and location executed) in place of the statement that "myApp/Foo.class is placed in a JAR file called MyJar.jar" would be much more clear.

[Karol Kornecki]

Hi

I think the correct answer should be:

 javac -classpath MyJar.jar GetJar.java  
 java -classpath MyJar.jar:. GetJar    

or

 javac -classpath MyJar.jar GetJar.java  
 java -classpath .:MyJar.jar GetJar    

when I compile and run the program as above it prints 8.