Re: Singletons?

"Oliver Wong" <>
Tue, 13 Jun 2006 19:45:28 GMT
"Ian Shef" <invalid@avoiding.spam> wrote in message

Mark Space <> wrote in news:FEDjg.147331$F_3.107067

How was I to implement
singleton objects then? Well, a quick web search and I've got the
answer, but now I have a few other questions on the JVM and compiler.

Let's say I have a class entirely of static methods:

public class anAPI {
     static void methodA {}
     static void methodB {}

I don't know the answer to your questions, but you can sidestep the
by defining a no-argument constructor and giving it the "private" keyword.
This way, there is no way that this class can be instantiated unless one
its own static methods does the deed. [Well, maybe there is a cheat via

    I didn't assume that the anAPI class was the OP's implementation of the
Singleton design pattern, but perhaps I should have. FWIW, here's how I
usually implement Singleton in Java:

public class Variant1 {
  private static Variant1 soleInstance = null;

  private Variant1() {
    /*You should declare all your constructors private, to avoid
instantiation. If you don't have any constructors, then create an empty,
zero argument, private constructor like this one.*/

  public static Variant1 getSoleInstance() {
    if (soleInstance == null) {
      soleInstance = new Variant1();
    return soleInstance;

  private Object instanceFields;
  public void instanceMethods() {

public class Variant2 {
  private final static Variant2 soleInstance = new Variant2();

  private Variant2() {

  public static Variant2 getSoleInstance() {
    return soleInstance;

  private Object instanceFields;
  public void instanceMethods() {

    - Oliver

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