Re: Updates to a single class instance

From:

Theme <therne@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 21 Aug 2007 16:31:47 -0000

Message-ID:

<1187713907.432750.119220@19g2000hsx.googlegroups.com>

On Aug 18, 10:42 pm, unlikeablePorpo...@gmail.com wrote:

package org.collector;

public class Collector{

        private Collector() {}

        private static Collector ref;

        public static synchronized Collector getCollectorObject()
        {
                if(ref == null)
                {
                        System.out.println("ref is null");
                        ref = new Collector();
                }
                else
                {
                        System.out.println("ref exists");
                }

                return ref;
        }

}

When I call 'Collector col = Collector.getCollectorObject();' twice in
two different classes, it returns "ref is null". However, if I do this
twice in the same class method, ie

Collector col = Collector.getCollectorObject();
Collector col2 = Collector.getCollectorObject();

I get the expected result:

"ref is null"
"ref exists"

IMHO it's ok, since it ptints to System.out message from block with
lazy initialization,
it does not return null, does it?

         private Collector() {}
         private static Collector ref;

         public static synchronized Collector getCollectorObject()
         {
                 if(ref == null)
                 {
                          System.out.println("lazy initialization!
here, IMHO static will be better...");
                         ref = new Collector();
                 }
                 else
                 {
                         System.out.println("ref exists");
                 }

                 return ref;//does not return null object in any case!
         }
(first time will print to System.out "lazy initialization! here...")
And yes, removing lazy initialization will make class more concurrent-
compatible.

Good Luck, Theme