[Java] About Singleton Class

Hello ^^ I'm Nguyen working for an IT company in Tokyo. It's my first post, so it's a little exciting. ^^ Here are some things to remember when studying Java SE8 Gold. Immediately, I would like to make a note about the singleton class.

What is a singleton

** Singleton ** is one of the design patterns that guarantees that no more than one instance of a class is created.

Therefore, singletons are generally implemented according to the guidelines listed below.

  1. Declare a private static field, create a single instance of itself and set it in that field. ⇒ Motivation: Create only one instance and always refer to only that one instance.
  2. Declare the constructor private. ⇒ Motivation: Prevent instantiation from outside (can be instantiated only inside the class)
  3. Provide a public static method that returns an instance set in its own field. ⇒ Motivation: To be able to get an instance reference of this class from the outside.

Singleton class implementation example:


public class Foo {
    private static final Foo foo = new Foo();
    private Foo();
    public static Foo getInstance() {
        return foo;

Get an instance of a singleton class from the outside.

Foo foo = Foo.getInstance();


How about everyone? I hope you understand the singleton class even a little. ^^ See you in the next post! Bye bye!

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