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javac++staticsingletonlazy-initialization

Initialization On Demand Holder idiom

This is the implementation mostly seen on the web 

private static class LazySomethingHolder {
  public static Something something = new Something();
}

public static Something getInstance() {
  return LazySomethingHolder.something;
}

Is the following simpler variation correct, if not what is wrong with it? Is the problem specific to java or also present in C++?

public static Something getInstance() {
  private static Something something = new Something();
  return something;
}
Solution

  • You cannot have static local variables in Java.

    Simpler alternatives are

    private static final Something something = new Something();

public static Something getInstance() {
  return something;
}

    or my preference if for.

    enum Something {
    INSTANCE;
}

    The only problem with these patterns is that if you have multiple instances you want lazily loaded, you need to have a class each, or loading one will mean loading them all.