The Singleton pattern restricts how instances are created and accessed. This article follows eager initialization, double-checked locking, the holder idiom, and enums, explaining their initialization behavior and limits.

Technical review (2026-10-13): These patterns remain applicable. The discussion is checked against the Java 5+ memory model and Java SE 25 specifications. It corrects the loading/initialization distinction, runtime access checks, and the explanation of enum reflection. The code blocks named Singleton are alternatives, not declarations to combine in one source file.