why we use private constructor in flutter sqlite databse

Question

What is the use of this private constructor and why we instantiate it's object under the class.

DatabaseHelper._privateConstructor();
static final DatabaseHelper intance =DatabaseHelper._privateConstructor();

Answer 1

In general, we'll use a private constructor when we don't want things to be instantiated more than once. This lets us implement the singleton pattern:

https://www.geeksforgeeks.org/singleton-design-pattern/

In this case, we don't want multiple instance of the database. So, it'll instantiate the database if it hasn't already been instantiated, or it'll return the existing instance of the database if it has been instantiated previously.

Answer 2

It is a design pattern called the singleton pattern.

It's main purpose is to ensure that only one instance of that class ever exists in the application.

To ensure this purpose, the pattern implements techniques that have serious disadvantages. People are overusing it, sometimes using it as a justification as to why they have those disadvantages in their program that would otherwise be considered bad design. It has become an anti-pattern. See Why is Singleton considered an anti-pattern?.

Answer 3

In addition to given answers, it is Eager singleton, therefore once the class is initialized, the instance is also initialized, even the instance is not used. However still it has been instantiated only once.

See also Singleton lazy vs eager instantiation

Answer 4

As the other answers state, it's the singleton pattern. Here's a link that explains it more.