Why do I need 2 statements for instantiation vs. 1?

[Janet Wilson]

I was reading this great article re: Factory Methods from Javaworld: Factory Methods
when I stumbled upon their code which I have cut and pasted here because I am experiencing a problem with it. My question is why do I need to use 2 statements for instantiation in my TraceExample.java because I can't get it to work with just the 1 which was provided in the article? Also, by using 2 stmts, will that ruin the Factory Method pattern (figured I'd sneak that question even if it might belong in the OO category).
Here is the Trace.java....

 public interface Trace {
      // turn on and off debugging
      public void setDebug( boolean debug );
      // write out a debug message
      public void debug( String message );
      // write out an error message
      public void error( String message );
} 

Here is the SystemTrace.java...

 public class SystemTrace implements Trace {
      private boolean debug;
      public void setDebug( boolean debug ) {
            this.debug = debug;
      }
      public void debug( String message ) {
            if( debug ) {  // only print if debug is true
                  System.out.println( "DEBUG: " + message );
            }
      }
      public void error( String message ) {
            // always print out errors
            System.out.println( "ERROR: " + message );
      }
}
 

Here is the TraceFactory.java....

public class TraceFactory {
      public static Trace getTrace() {
            System.out.println("Executing the TraceFactory program");
            return new SystemTrace();
      }
}  

And lastly, the TraceExample.java....

class TraceExample  {
  public static void main (String args[])
  {
    System.out.println("Executing the TraceExample program");
    TraceFactory tracefactory = new TraceFactory();
    Trace log = tracefactory.getTrace();
    System.out.println("Just finished running the Trace log stmt using getTrace()");
/*Trace log = new TraceFactory.getTrace();<==This line does not work if lines 6 & 7 are commented--why?
    System.out.println("Just finished running the Trace log stmt using getTrace()");
*/
    log.debug( "entering loog" );
  }
}  

Thanks folks! It's probably one of those end of the work week types of things which is blinding me to the solution.
Janet
[ December 13, 2002: Message edited by: Janet Wilson ]

[Maulin Vasavada]

hi Janet,

Trace log = new TraceFactory.getTrace();<==This line does not work if lines 6 & 7 are commented--why?

here i observe one thing. u r using,
new TraceFactory.getTrace();
why u have put "new"? the object is returned from TraceFactory right?
OR if that was a type then i am not sure what is causing the problem.
regards
maulin

[Janet Wilson]

Thanks Maulin!
I removed the new and changed the commented lines and it works!

[Ilja Preuss]

Of course you could also have called the method on a factory instance, but then you had to complete the constructor call with parentheses:
Trace log = new TraceFactory().getTrace();

[Janet Wilson]

You are right - this works, too. The author probably meant this. Thanks Ilja!