I am reading the book java An object-oriented Approach by Arnow and
Weiss and am wondering why a sample code that is provided in the book
does not work.  Please help me fix the code so it works and explain
why it did not work (it is the exact code in the book).  I am using
NetBeans IDE 3.5.1 with J2SE 1.4.2.

import java.net.*;
import java.io.*;

public class WHWWW {
    
    public static void main(String[] args) throws Exception {
        URL u = new URL("http://www.whitehouse.gov/");
        FilterInputStream ins = u.openStream();
        InputStreamReader isr = new InputStreamReader(ins);
        BufferedReader whitehouse = new BufferedReader(isr);
        System.out.println(whitehouse.readLine());
        System.out.println(whitehouse.readLine());
        
    }
    
}

Hi,

Thank you for your question. Here is the correct code. You will see
that the change is very minor:

package counting;

import java.net.*;
import java.io.*;

public class WHWWW {

    public static void main(String[] args) throws Exception {
        URL u = new URL("http://www.whitehouse.gov/");
        FilterInputStream ins = (FilterInputStream)u.openStream();
        InputStreamReader isr = new InputStreamReader(ins);
        BufferedReader whitehouse = new BufferedReader(isr);
        System.out.println(whitehouse.readLine());
        System.out.println(whitehouse.readLine());

    }

}


You need specifically cast the InputStream into a FilterInputStream,
that's what (FilterInputStream) does. The Java compiler does not allow
you to use FilterInputStream where InputStream is expected.

There are other (more complicated) solutions provided on:

javajunkies
http://www.javajunkies.org/index.pl?lastnode_id=458&node_id=1034


I hope this answers your question. If anything is unclear or you
require any clarifications, please do not hesitate to ask.

Thanks.
endo

---

Request for Answer Clarification by brianct-ga on 20 Dec 2003 19:17 PST

Though your answer (and the comment) was extremely helpful, I am still
getting this

error: cannot read: C:\Documents; and
Settings\brian\.netbeans\3.5\sampledir\WHWWW.java
1 error
Errors compiling.

I copied your exact code and the code from the comment.

---

Clarification of Answer by endo-ga on 20 Dec 2003 20:29 PST

Hi,

Can you please try creating a new file in another directory and try
compiling it again please?

The code definitely works, I've tried it, so it must be some other
problem. Try putting the file in C:\j2sdk1.4.2\bin and compile it from
please. Please make sure it is not write protected or anything like
that.

Thanks.
endo

Thanks for the help.

I checked the errata for the book and sure enough there is a problem with the
code you were trying to use. The errata can be found here:

ftp://ftp.aw.com/cseng/authors/arnow/Java2SourceCode/Errata.txt

The relevent entry states:

---------
Chapter 3
---------

- page 79- The WHWWW class contains two typos:
    
- A 'throws Exception' is missing from the signature of the 'main' method
    
- The declaration:
	FilterInputStream ins = u.openStream();
    shoud read:
	InputStream ins = u.openStream();

- The online source code contains the correct version.

The online code can be found here:

ftp://ftp.aw.com/cseng/authors/arnow/Java2SourceCode/

The corrected code is:

import  java.net.*;
import java.io.*;

class WHWWW {
   public static void main(String[] arg) throws Exception {
   		URL u = new URL("http://www.whitehouse.gov/");
		InputStream ins = u.openStream();
		InputStreamReader isr = new InputStreamReader(ins);
		BufferedReader whiteHouse = new BufferedReader(isr);
		System.out.println(whiteHouse.readLine());
		System.out.println(whiteHouse.readLine());
		System.out.println(whiteHouse.readLine());
		System.out.println(whiteHouse.readLine());
		System.out.println(whiteHouse.readLine());
	}
}

The problem with the original code is that it tries to assign the
object returned by the openStream method of the URL class, which in
the API is declared to be of type InputStream, to a variable of type
FilterInputStream. The relevent line is:

FilterInputStream ins = u.openStream();

This will cause a compile time error, since it attempts a narrowing
conversion without a cast. In plane English this means that you're
trying to store an object of a given class in a variable that's
declared to be a more specific class. If you knew that the object
returned was in fact a FilterInputStream, or a subclass, then you
could correct the code by adding a narrowing cast, as in:

FilterInputStream ins = (FilterInputStream )u.openStream();

This will now compile. However, it's not correct, since we don't know,
and shouldn't care, what the actual type of the object returned is. In
fact if you were to check, by printing the class of the object, you'd
find it was an instance of the HttpURLConnection class.

Hope this helps.

Cheers,

Eadfrith

I don't believe the problem is with your code but with the java 
compiler getting confused by the spaces in the location of the file. 
I've not used netbeans, but it appears that when you try to compile 
your class it's issuing the command:

javac C:\Documents and Settings\brian\.netbeans\3.5\sampledir\WHWWW.java

which is fine, except that javac sees the spaces in the "Document and 
Settings" and breaks up the command line. This is an issue under 
windows.

How to fix it? If this was the command line you could simple put quotes 
around the filename, as in 

javac "C:\Documents and Settings\brian\.netbeans\3.5
\sampledir\WHWWW.java"

but since netbeans is issuing the compile command I'm not sure how to 
cause it to do this.

The simpler solution would be to create your project in a location 
other than "Documents and Settings\brian", which is the actual location 
of the "My Documents" folder under windows. Create it in a location 
which doesn't have any spaces and you should be fine.

Cheers,

Eadfrith

Thank you for the great rating and generous tip.
Regards,
endo