Thread doubled output

Question

Hi,
For the purpose of my work, I am trying to store the output that is produced by StreamRedirectThread.java into a vector as shown in the code below. The output of the thread code is ok and the output printed is the numbers from 0 to 5.
When I try to print out that vector, the output is not as the same as it is printed in the StreamRedirectThread.java program. For example if the output form the program prints out the numbers form 0 to 5, as I said before, the vector output is doubled in size and prints:
index = 0 content=0
index = 1 content=
index = 2 content=1
index = 3 content=
index = 4 content=2
index = 5 content=
index = 6 content=3
index = 7 content=
index = 8 content=4
index = 9 content=
index = 10 content=5
index = 11 content=
Can anybody advice me what to do about it. I tried but couldn't fix it. The code of StreamRedirectThread.java is as
Here is the Thread Code: Thanks
import java.io.*;*
*import java.util.*;
import com.sun.jdi.*;*
*import com.sun.jdi.request.*;
import com.sun.jdi.event.*;*
*import com.sun.jdi.connect.*;
class StreamRedirectThread extends Thread {
private final Reader in;
private final Writer out;
private static Vector outvector = new Vector(0); // victor of objects that contains output result
private static final int BUFFER_SIZE = 2048;
* Set up.
* @param name Name of the thread
* @param in Stream to copy from
* @param out Stream to copy to
StreamRedirectThread(String name, InputStream in, OutputStream out) {
super(name);
this.in = new InputStreamReader(in);
this.out = new OutputStreamWriter(out);
setPriority(Thread.MAX_PRIORITY-1);
public void run() {
try {
char[] cbuf = new char[BUFFER_SIZE];
int count;
while ((count = in.read(cbuf, 0, BUFFER_SIZE)) >= 0) {
//out.write(cbuf,0,count);
String s = new String(cbuf,0,count);
if (!(s.equals(null)))
TemplateApp.vv.addElement(s);
outvector.addElement(s); out.write(s);
out.flush();
} catch(IOException exc) {
System.err.println("Child I/O Transfer - " + exc);
public synchronized static Vector getOutVector()
return outvector ;
}Thanks a lot for help

Answer 1

Iman_S wrote:
while ((count = in.read(cbuf, 0, BUFFER_SIZE)) >= 0) {
   String s = new String(cbuf,0,count);
   if (!(s.equals(null)))
      TemplateApp.vv.addElement(s);
   outvector.addElement(s); out.write(s);
   out.flush();
}I've reposted and properly indented this code to help you understand what's going on. I have many problems with this:
1. s.equals(null) is always false if equals is properly implemented. This is because, if a.equals(b), b.equals(a) must be true due to the symmetry constraint of equals() -- see here: [http://java.sun.com/developer/Books/effectivejava/Chapter3.pdf]. If s.equals(null) were true, then null.equals(s) would have to be true, which is obviously incorrect as a NullPointerException would have been thrown. Use s == null to compare an Object reference with a null reference, and use s.isEmpty() or s.length() == 0 to decide whether a String has characters.
2. Always use opening and closing braces ( { } ) with an if block. I'm guessing you thought that the "outvector.addElement(s)" statement was IN the if block, but it in fact wasn't. Always be explicit.
3. Don't do anything that you're doing inside that while loop if count == 0. in.read() can return 0 any time it wants, which means that it didn't read any characters. However, you are using that blank output without caring. I'm guessing the s.equals(null) line was meant to weed that out, but as I said, that will always be false. Moreover, new String( new char[0] ) doesn't give you a null reference, it gives you a new String with no characters.
I would suggest something more like this:
while ((count = in.read(cbuf, 0, BUFFER_SIZE)) >= 0) {
   if ( count == 0 ) {
      continue;
   String s = new String(cbuf,0,count);
   TemplateApp.vv.addElement(s);
   outvector.addElement(s);
   out.write(s);
   out.flush();
Edit I should note that this isn't likely your problem. As Peter said, it does look like you are basically adding newline characters to outvector (if you're sending your data with println, this is to be expected!). Also, I was a bit hasty in saying that InputStream returns 0 "whenever it wants." This isn't typical behaviour, but it should be handled nonetheless.
Remember that the whole idea of quantifying a Stream like you're doing (adding the content piece by piece to a vector) doesn't make much sense. You really don't have control over how much data arrives at once, etc. This usually depends on the implementation of the streams that are receiving and sending the data. So, while if I sent this string over a socket:
"Hello brave new world"
And received it with a large buffer, it could be read by your in.read() function in these pieces: "Hello ", "brave ", "new ", "world", but that would be completely coincidental. It's more likely it would arrive in random pieces, and most likely in one big piece, requiring only one in.read().
Edited by: endasil on 22-Jul-2008 3:59 PM