Calls to methods in a class that extends Thread

Question

Hello,
I have some code that I am initiating from within an ActionListener that is part of my programs GUI. The code is quite long winded, at least in terms of how long it takes to perform. The code runs nicely, however once it is running the GUI freezes completely until operations have completed. This is unacceptable as the code can take up to hours to complete. After posting a message on this forum in regard to the freezing of the GUI it was kindly suggested that I use multi-threading to avoid the unwelcome program behaviour.
The code to my class is as follows:
public class FullURLAddress
  private boolean success_flag = true;
  private BufferedReader iN;
  private Document dT;
  private EditorKit kT;
  private Element lmNt;
  private ElementIterator lmIterate;
  private XURL[] compAddress;
  private int countX = 0;           //Tracks Vector vT's size.
  private int countY = 0;           //Tracks Vector vS's size.
  private int xURLcount = 0;        //Tracks XURL objects instantiated by this FullURLAddress object.
  private SimpleAttributeSet simpAtSet;
  private String aURL;              //Contains original (Xtended) URL!
  private String fileType;
  private String indexContent;
  private String[] parseURL;
  private String[] finalStrings;
  private String[] sortStrings;
  private URL indexConnect;
  private URLConnection iconn;
  private Vector vT;            //Stores href information, from targeted URL's HTML souce code.
  private Vector vS;            //Stores sorted HREF info ".jpg" and ".gif" only (no: png, tiff, etc).
  public FullURLAddress(String aURL)
    this.aURL = aURL;
    try{
      indexConnect = new URL(aURL);
      iconn = indexConnect.openConnection();
      iN = new BufferedReader(new InputStreamReader(iconn.getInputStream()));
        /* Document creation, analysis objects instantiated */
      vT = new Vector();
      vS = new Vector();
      kT = new HTMLEditorKit();
      dT = kT.createDefaultDocument();
      dT.putProperty("IgnoreCharsetDirective", Boolean.TRUE);
        /* Iterate through document and store all HREF values */
      kT.read(iN, dT, 0);
      lmIterate = new ElementIterator(dT);
      while((lmNt = lmIterate.next()) != null)
        simpAtSet = (SimpleAttributeSet)lmNt.getAttributes().getAttribute(HTML.Tag.A);
        if(simpAtSet != null)         //As long as there are A tags to be read...
          vT.addElement(simpAtSet.getAttribute(HTML.Attribute.HREF));
          countX++;//Tracks number of HREF occurences occur, giving better control of the Vector.
    }catch(MalformedURLException e){
      success_flag = false;
      System.out.println("FullURLAddress object has encountered a "+
                         "MalformedURLException at: "+aURL);
    }catch(IOException e){
      e.getMessage();
      success_flag = false;
    }catch(BadLocationException e){
      e.getMessage();
      success_flag = false;
    /* Searches through all HREF attributes that are now stored in Vector
       vT for occurences of the character string ".htm" */
    sortStrings = new String[countX];
    for(int i=0;i<countX;i++)
      sortStrings[i] = (String)vT.elementAt(i); //Vector Strings transfered into array.
      if(sortStrings.endsWith("gif")) // Does href value end with ".jpg"?
vS.addElement(sortStrings[i]); // If so add it to the sorted Vector vS.
countY++;
if(sortStrings[i].endsWith("GIF"))
vS.addElement(sortStrings[i]);
countY++;
if(sortStrings[i].endsWith("jpg")) // Does href value end with ".jpg"?
vS.addElement(sortStrings[i]); // If so add it to the sorted Vector vS.
countY++;
if(sortStrings[i].endsWith("JPG"))
vS.addElement(sortStrings[i]);
countY++;
finalStrings = new String[countY];
for(int j=0;j<countY;j++)
finalStrings[j] = (String)vS.elementAt(j);
public int getCount()
return countY; //Returns number of instances of htm strings
} //ending with either "jpg" or "gif".
public String[] xurlAddressDetails()
return finalStrings;
I have changed the above code to make use of multithreading by making this class extend Thread and implementing the run() method as follows:
public class FullURLAddress extends Thread
  private boolean success_flag = true;
  private BufferedReader iN;
  private Document dT;
  private EditorKit kT;
  private Element lmNt;
  private ElementIterator lmIterate;
  private XURL[] compAddress;
  private int countX = 0;           //Tracks Vector vT's size.
  private int countY = 0;           //Tracks Vector vS's size.
  private int xURLcount = 0;        //Tracks XURL objects instantiated by this FullURLAddress object.
  private SimpleAttributeSet simpAtSet;
  private String aURL;              //Contains original (Xtended) URL!
  private String fileType;
  private String indexContent;
  private String[] parseURL;
  private String[] finalStrings;
  private String[] sortStrings;
  private URL indexConnect;
  private URLConnection iconn;
  private Vector vT;            //Stores href information, from targeted URL's HTML souce code.
  private Vector vS;            //Stores sorted HREF info ".jpg" and ".gif" only (no: png, tiff, etc).
  public FullURLAddress(String aURL)
    this.aURL = aURL;
  public void run()
    try{
      indexConnect = new URL(aURL);
      iconn = indexConnect.openConnection();
      iN = new BufferedReader(new InputStreamReader(iconn.getInputStream()));
        /* Document creation, analysis objects instantiated */
      vT = new Vector();
      vS = new Vector();
      kT = new HTMLEditorKit();
      dT = kT.createDefaultDocument();
      dT.putProperty("IgnoreCharsetDirective", Boolean.TRUE);
        /* Iterate through document and store all HREF values */
      kT.read(iN, dT, 0);
      lmIterate = new ElementIterator(dT);
      while((lmNt = lmIterate.next()) != null)
        simpAtSet = (SimpleAttributeSet)lmNt.getAttributes().getAttribute(HTML.Tag.A);
        if(simpAtSet != null)         //As long as there are A tags to be read...
          vT.addElement(simpAtSet.getAttribute(HTML.Attribute.HREF));
          countX++;//Tracks number of HREF occurences occur, giving better control of the Vector.
    }catch(MalformedURLException e){
      success_flag = false;
      System.out.println("FullURLAddress object has encountered a "+
                         "MalformedURLException at: "+aURL);
    }catch(IOException e){
      e.getMessage();
      success_flag = false;
    }catch(BadLocationException e){
      e.getMessage();
      success_flag = false;
    /* Searches through all HREF attributes that are now stored in Vector
       vT for occurences of the character string ".htm" */
    sortStrings = new String[countX];
    for(int i=0;i<countX;i++)
      sortStrings[i] = (String)vT.elementAt(i); //Vector Strings transfered into array.
      if(sortStrings.endsWith("gif")) // Does href value end with ".jpg"?
vS.addElement(sortStrings[i]); // If so add it to the sorted Vector vS.
countY++;
if(sortStrings[i].endsWith("GIF"))
vS.addElement(sortStrings[i]);
countY++;
if(sortStrings[i].endsWith("jpg")) // Does href value end with ".jpg"?
vS.addElement(sortStrings[i]); // If so add it to the sorted Vector vS.
countY++;
if(sortStrings[i].endsWith("JPG"))
vS.addElement(sortStrings[i]);
countY++;
finalStrings = new String[countY];
for(int j=0;j<countY;j++)
finalStrings[j] = (String)vS.elementAt(j);
/* What happens with these methods, will they need to have their
own treads also? */
public int getCount()
return countY; //Returns number of instances of htm strings
} //ending with either "jpg" or "gif".
public String[] xurlAddressDetails()
return finalStrings;
Are there any special things that I need to do in regard to the variables returned by the getCount() and xurlAddressDetails() methods. These methods are called by the code that started the run method from within my GUI. I don't understand which thread these methods are running in, obviously there is an AWT thread for my GUI and then a seperate thread for my FullURLAddress objects, but does this new thread also encompass the getCount() and xurlAddressDetails() methods?
Please explain.
This probably sounds a little wack, but I don't understand what thread is responisble for the methods in my FullURLAddress class aside of course from the run() method which is obvious. Any help will be awesome.
Thanks
Davo

Answer 1

Threads are part of code that allows you to run multiple operations "simultaneously". "Simultaneously", because threads are not run actually simultaneously in any one-CPU machine. Since you most propably have only one CPU in your system, you can only execute one CPU instruction at time. Basically this means that your CPU can handle only one java-operation at time. It does not matter if you put some code in thread and start it, it will still take up all CPU time as long as the thread runs.
So you would need a way to let other threads run also, for that purpose thread contains a yield feature that allows you to give time for other threads to run.
http://java.sun.com/j2se/1.4.1/docs/api/java/lang/Thread.html#yield()
You need to use thread's yield() method in your thread code, in a place you want to give other threads time to run. Also bear in mind that if you yield your first thread run to allow second thread to run, you also need to add yield to the second thread also. If you don't, after yielding the first thread, the second thread will eat up all CPU time until it finishes, thus meaning the rest of your first thread will be run after second thread is done.
One good place to execute yield() is usually at the end of a loop, for example 'for' or 'while' loop. This way you prevent for example while-deadlocks.
Here is a java thread tutorial, worthy reading:
http://java.sun.com/docs/books/tutorial/essential/threads/