singleton pattern in java

[jayakumar elumalai]

I have heard about using patterns in core java.Is it possible?If yes, how?

[subhit chauhan]

patterns are designing stuff.... you can use any types of patterns in any technology.... check this link out http://www.patterndepot.com/put/8/JavaPatterns.htm
for Java design patterns.....

[Dirk Schreckmann]

For example, a Java implementation of the Singleton Pattern might be as follows.

public class Foo
{
  private static final instance = new Foo();
  
  private Foo()
  {
    
  }
  
  public static Foo getInstance()
  {
    return instance;
  }
}

[Stan James]

As you study singletons, be aware of a pattern once (but no longer) recommended by Sun that has been shown not to work on multi-processor machines and in some cases in multi-threaded apps on a single processor. If you see code like:

  
class SomeClass {
  private Resource resource = null;
  public Resource getResource() {
    if (resource == null) {
      synchronized {
        if (resource == null) 
          resource = new Resource();
      }
    }
    return resource;
  }
}

Run away! Here is an article on whyDouble-Checked Locking can get you in trouble.

[John Smith]

The Singleton
Oh Singleton, -- to use or not to use?
The grace of pattern overwhelms me, --
You've been the subject of abuse,
Or so the sheriffs try to tell me
The heat of virtual hot spot machine
Makes my initializers slow and lazy
But the class loaders are really mean,
They make two instances, amazing!
And then the garbage man comes in
To claim the memory unreferenced
And when I call it from the bean
It's doubleton, as if I had no preference!
The call to get an instance comes along,
But gets preempted by someone to blame.
I now have a tripleton, and I am prone
To crashes, errors, tears, and pain.