Re: singleton

Thomas Fritsch <>
Fri, 22 Sep 2006 17:33:59 GMT
<newscache$ns806j$nm1$> wrote:

I saw two ways of instantiate singleton.
Somebody can help me compare those two. ( with multi-thread in mind).

private static final MyClass singleton = new MyClass();
public static MyClass getInstance()
  return singleton;

2) Lazy and thread safe
static private class Holder
static protected final MyClass instance= new MyCLass();

public static MyClass getInstance()
  return MyClass.Holder.instance;

3) Lazy and thread-safe
private static MyClass singleton;
public synchronized static MyClass getInstance()
   if (singleton == null)
     singleton = new MyClass();
   return singleton;

IMHO all 3 implementations are equivalent with respect to thread-safety.
But they are different with respect to memory/time-consumption.

(1) has the advantage of being simple.
And, by the way, it is thread-safe, too.
It has the disadvantage of creating the MyClass instance, even if it is
never needed. This may be an issue, if the MyClass constructor loads a
lot of classes or does other memory/time-consuming actions.

(2) and (3) have the advantage of creating the MyClass instance lazy,
i.e. as late as possible. This may save some memory/time, if the
getInstance() method is never called.


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