Re: Singleton vs static

Lew <>
Wed, 05 Dec 2007 13:41:17 -0500
Philipp wrote:

Lew wrote:

Philipp wrote:

Lew wrote:

Philipp wrote:

My POV: No, you can put a state in a static var and access it
through static methods.

Which breaks as soon as two different instances need different state
at the same time.

If you need _two_ instances its not a singleton anymore, is it?

Two different *client* instances, duhy!

OK sorry. I don't understand.
Do you mean I have to synchronize the access to the static var?

Synchronization won't help. The problem generally is the problem with global

<sscce source="testit/" >
package testit;

import java.util.Random;

class Foo
   volatile private static String global;
   public static void setGlobal( String g )
   { global = g; }
   public static String getGlobal()
   { return global; }

/** SnoGlobal - The answer to "What's a good global?"
public class SnoGlobal implements Runnable
   private final String name;
   public SnoGlobal( String f )
   { = f;
   public void run()
     Random ran = new Random();

     for ( int ix = 0; ix < 3; ++ix)
         Foo.setGlobal( name );
             Thread.sleep( ran.nextInt( 5000 ) );
         catch ( InterruptedException ex )
             System.err.println( "Interrupted "+ name );
         System.out.println( "Instance " + name + ", global " +
                 Foo.getGlobal() );

   public static void main( String [] args )
     SnoGlobal baron = new SnoGlobal( "baron" );
     SnoGlobal tobar = new SnoGlobal( "tobar" );
     new Thread( baron ).start();
     new Thread( tobar ).start();

Instance tobar, global tobar
Instance baron, global tobar
Instance tobar, global baron
Instance tobar, global tobar
Instance baron, global tobar
Instance baron, global baron


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