about Sun Guoqiao's mock-exam-02-38

[galen wang]

mock-exam-02-38:

<font "monospaced" size=+0>
    public class Test038
    {
        public static void main(String args[])
        {
            new Test038().new Nested().method("first"); //1
            new Test038().Nested.method("second");      //2 
            Test038.Nested.method("third");             //3
        }
        static class Nested
        {
            static void method (String caller)          //4
            {
                System.out.println(caller);
            }
        }
    }

-----------------------------------------------------------------------
A: The code does not compile due to line //1.
B: The code does not compile due to line //2.
C: The code does not compile due to line //3.
D: The code compiles and runs with output:
first
second
third

---

</BLOCKQUOTE>
I think the correct answer is A.
that is because the class "Nested" is a top-level nested class (it's static), generally we can use below three ways to call the methord.
new Test038().Nested.method("by instance of Test038");
new Test038.Nested().method("by instance of Nested");
Test038.Nested.method("direct by class name");
but the answer and explanation is

Answers:
: B
Explanation:
: //2 tries to access Nested as if it is a variable
of Test038, which is not the case.

I can't agree with that and try to compile and run it.
the compile result is
Test038.java:5: qualified new of static class
new Test038().new Nested().method("first"); //1
then i modified the
new Test038().new Nested().method("first"); //1 => new Test038.Nested().method("first") //1;
it compiles and runs. the output is
first
second
third
wath's wrong in the Test038's answer?
I found that different java vesion will bring different result. (above I use jdk1.4.)
I tried jdk1.2.2, to the origin code the compile result is
Test038.java:7: No variable Nested defined in class Test038.
new Test038().Nested.method("second"); //2
if I commended this line then the compile was ok but the run result is
Exception in thread "main" java.lang.VerifyError: (class: Test038, method: main signature: ([Ljava/lang/String V) Expecting to find unitialized object on stack
I also tried jdk1.3.0_02, to the origin code the compile result is awful, it gives
An exception has occurred in the compiler (1.3.0_02). Please file a bug at the Java Developer Connection (http://java.su
n.com/cgi-bin/bugreport.cgi). Include your program and the following diagnostic in your report. Thank you.java.lang.NullPointerException
at com.sun.tools.javac.v8.comp.TransInner.access(TransInner.java:725)
at com.sun.tools.javac.v8.comp.TransInner._case(TransInner.java:1563)
at com.sun.tools.javac.v8.tree.Tree$Select.visit(Tree.java:963)
at com.sun.tools.javac.v8.tree.TreeTranslator.translate(TreeTranslator.java:35)
at com.sun.tools.javac.v8.comp.TransInner._case(TransInner.java:1557)
at com.sun.tools.javac.v8.tree.Tree$Select.visit(Tree.java:963)
at com.sun.tools.javac.v8.tree.TreeTranslator.translate(TreeTranslator.java:35)
at com.sun.tools.javac.v8.comp.TransInner._case(TransInner.java:1490)
at com.sun.tools.javac.v8.tree.Tree$Apply.visit(Tree.java:785)
at com.sun.tools.javac.v8.tree.TreeTranslator.translate(TreeTranslator.java:35)
at com.sun.tools.javac.v8.tree.TreeTranslator._case(TreeTranslator.java:179)
at com.sun.tools.javac.v8.tree.Tree$Exec.visit(Tree.java:699)
at com.sun.tools.javac.v8.tree.TreeTranslator.translate(TreeTranslator.java:35)
at com.sun.tools.javac.v8.tree.TreeTranslator.translate(TreeTranslator.java:47)
at com.sun.tools.javac.v8.tree.TreeTranslator._case(TreeTranslator.java:111)
at com.sun.tools.javac.v8.tree.Tree$Block.visit(Tree.java:492)
at com.sun.tools.javac.v8.tree.TreeTranslator.translate(TreeTranslator.java:35)
at com.sun.tools.javac.v8.tree.TreeTranslator._case(TreeTranslator.java:100)
at com.sun.tools.javac.v8.comp.TransInner._case(TransInner.java:1423)
at com.sun.tools.javac.v8.tree.Tree$MethodDef.visit(Tree.java:441)
at com.sun.tools.javac.v8.tree.TreeTranslator.translate(TreeTranslator.java:35)
at com.sun.tools.javac.v8.comp.TransInner._case(TransInner.java:1360)
at com.sun.tools.javac.v8.tree.Tree$ClassDef.visit(Tree.java:402)
at com.sun.tools.javac.v8.tree.TreeTranslator.translate(TreeTranslator.java:35)
at com.sun.tools.javac.v8.comp.TransInner.translate(TransInner.java:1322)
at com.sun.tools.javac.v8.comp.TransInner.translateTopLevelClass(TransInner.java:1588)
at com.sun.tools.javac.v8.JavaCompiler.compile(JavaCompiler.java:397)
at com.sun.tools.javac.v8.Main.compile(Main.java:247)
at com.sun.tools.javac.Main.main(Main.java:16)
my conclusion is:
1. befor version jdk1.4 there was bugs in treating inner class.
2. the correct answer of Test038 should be A not B.

[This message has been edited to add code tags]
[This message has been edited by Marilyn deQueiroz (edited October 05, 2001).]

[Marilyn de Queiroz]

> An exception has occurred in the compiler (1.3.0_02). Please
> file a bug at the Java Developer Connection (http://java.sun.com/cgi-bin/bugreport.cgi).

Yes, this is the result I also got.

[Guoqiao Sun]

Hi, galen:
I am using jdk1.3.0, as to mock-exam-02-38,
The code give the following compile error when I compile it:

Test038.java:9: No variable Nested defined in class Test038.
            new Test038().Nested.method("second");
                         ^
1 error

If I comment //2 out, the code compiles and runs without any error.
I don't know where is the problem. Please test it again and confirm with me if really got something wrong here.
Best regards,

------------------
Guoqiao Sun
Sun Certified Programmer for Java™ 2 Platform
try my mock exam¹²³ at my homepage.

[Muhammad Farooq]

Regardless of what the problem is, I just comment out the Line 2 and it compiles and runs, so I agree with the answer B. Sun, I am not satisfied with your explanation as I am getting the same error message as Galen is getting. Can anybody explain why B is the answer.
--Farooq

[Guoqiao Sun]

Hi, galen and Farooq, I have modified the question to avoid confusion. Thank you very much for your nice feedback.
Best regards,


------------------
Guoqiao Sun
Sun Certified Programmer for Java™ 2 Platform
try my mock exam¹²³ at my homepage.

[galen wang]

Hi Guoqiao,
srry to bother you but owing to java's inperfect, growing and updating, modify our mind to synchronize with it seems unavoidable. for another example the mock-exam-01-15:

Select valid contructors for FileOutputStream.
(Select four correct answers)
-----------------------------------------------------------------------
-----------------------------------------------------------------------
A: FileOutputStream(File file)
B: FileOutputStream(File file, boolean append)
C: FileOutputStream(FileDescriptor fd)
D: FileOutputStream(FileDescriptor fd, boolean append)
E: FileOutputStream(String fileName)
F: FileOutputStream(String fileName, boolean append)

the answer and explanation is

Answers:
: A C E F
Explanation:
: Please refer to Java API for the details.

but from the API of JavaTM 2 Platform Std. Ed. v1.4.0, there is a FileOutputStream(File file, boolean append) existing. so the answers should include B.
it's annoy but ...
galen

[Muhammad Farooq]

Galen, "B" is NOT the correct answer. Please look in the API to confirm this. I am looking into the API of JDK 1.3. I have just checked the API of JDK 1.4, your point is valid Galen but I dont know how to take care of this issue, anyone any idea ???
--Farooq
[This message has been edited by Muhammad Farooq (edited October 07, 2001).]
[This message has been edited by Muhammad Farooq (edited October 07, 2001).]
[This message has been edited by Muhammad Farooq (edited October 07, 2001).]

[galen wang]

Hi Muhammad,
please check
http://java.sun.com/j2se/1.4/docs/api/index.html -> Class FileOutputStream
in the Constructor Summary, there are five constructors:
--------------------------------------------------------
FileOutputStream(File file)
FileOutputStream(File file, boolean append)
FileOutputStream(FileDescriptor fdObj)
FileOutputStream(String name)
FileOutputStream(String name, boolean append)
--------------------------------------------------------
click FileOutputStream, you will see
--------------------------------------------------------
FileOutputStream
public FileOutputStream(File file,
boolean append)
throws FileNotFoundExceptionCreates a file output stream to write to the file represented by the specified File object. If the second argument is true, then bytes will be written to the end of the file rather than the beginning. A new FileDescriptor object is created to represent this file connection.
First, if there is a security manager, its checkWrite method is called with the path represented by the file argument as its argument.
If the file exists but is a directory rather than a regular file, does not exist but cannot be created, or cannot be opened for any other reason then a FileNotFoundException is thrown.

Parameters:
file - the file to be opened for writing.
append - if true, then bytes will be written to the end of the file rather than the beginning
Throws:
FileNotFoundException - if the file exists but is a directory rather than a regular file, does not exist but cannot be created, or cannot be opened for any other reason
SecurityException - if a security manager exists and its checkWrite method denies write access to the file.
Since:
1.4
See Also:
File.getPath(), SecurityException, SecurityManager.checkWrite(java.lang.String)
--------------------------------------------------------
galen

[Guoqiao Sun]

Hi, galen, for mock-exam-01-15 maybe I have to declare that the mock exam is for jdk1.3 since not every candidate check the latest JDK specification that often.
Regards,

------------------
Guoqiao Sun
Sun Certified Programmer for Java™ 2 Platform
try my mock exam¹²³ at my homepage.

[Marilyn de Queiroz]

<font size=+0>
public class Test038
{
    public static void main( String args[] )
    {
        new Test038().new Nested().method("first"); //1
//        new Test038().Nested.method("second");    //2
        Test038 t038 = new Test038();               // 5a
        t038.Nested.method( "test" );               // 5b
        Test038.Nested.method("third");             //3
    }
    static class Nested
    {
        static void method (String caller)          //4
        {
            System.out.println(caller);
        }
    }
}

Seems like it works fine if you split it into two lines (see 5a plus 5b are equal to 2). I also see no reason for it not to work. It appears to me to be a bug, and not something that on the exam. If I saw it on the exam, I would answer 'D' since Nested is static and method is static.

[Guoqiao Sun]

Hi, Marilyn, I tested the code your suggested and got the same result as you, it really looks somewhat strange.
Regards,

Originally posted by Marilyn deQueiroz:
[CODE]
Seems like it works fine if you split it into two lines (see 5a plus 5b are equal to 2). I also see no reason for it [b]not to work. It appears to me to be a bug, and not something that on the exam. If I saw it on the exam, I would answer 'D' since Nested is static and method is static.[/B]

------------------
Guoqiao Sun
Sun Certified Programmer for Java™ 2 Platform
try my mock exam¹²³ at my homepage.