Overcomplicated singleton

[Miha-x64]

design-patterns-java/src/refactoring_guru/singleton/example/thread_safe/Singleton.java

Lines 43 to 52 in 7601425

	Singleton result = instance;
	if (result == null) {
	synchronized (Singleton.class) {
	result = instance;
	if (result == null) {
	instance = result = new Singleton(value);
	}
	}
	}
	return instance;

Why do you prefer this overcomplicated code instead of concise, simple, thread-safe, and lazy enough

private static final Singleton instance = new Singleton();

?

[bhaskar253]

private static final Singleton instance = new Singleton();
is actually the eager initialization which will cause a slowdown in your application during startup.

The alternatives that can be used in place of the above mentioned double-check synchronized lock
is Bill-Pugh's Singleton & Enums, both of these are thread-safe and allows lazy initialization.

[Miha-x64]

will cause a slowdown

This is wrong because classes are loaded lazily, according to JVM spec.
Enums are genereted in exactly same way: public static constants are assigned during static initialization.

[roeniss]

@Miha-x64 what spec do you reference exactly?

[Miha-x64]

@roeniss https://docs.oracle.com/javase/specs/jls/se16/html/jls-12.html#jls-12.4.1