Re: Thread-safe Singleton Design Implementation

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <>
Mon, 30 Jul 2007 21:39:02 -0400
yaru22 wrote:

I was reading Wikipedia about Singleton Design pattern and it had some
sample codes for the implementation.

Under Java example implementation, there was "A thread-safe Java
programming language lazy-loaded solution." But I don't understand why
it is thread-safe & lazy-loaded solution. Could anyone explain it?

This is the source code from the Wikipedia (
wiki/Singleton_pattern) :
public class Singleton
  // Private constructor suppresses generation of a (public) default
  private Singleton() {}

  private static class SingletonHolder
    private final static Singleton INSTANCE = new Singleton();

  public static Singleton getInstance()
    return SingletonHolder.INSTANCE;

I believe it is thread safe because class initialization is so and
it is lazy loaded because SingletonHolder will first be initialized
the first time Singleton.getInstance is called.

It is one of the weird approaches people take to avoid using
synchronized, which in most cases will work just fine.


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