CODEWITHSUNDEEP
java
Prashant Pandey
Prashant Pandey

Reputation: 4652

Global State in Singletons

I was going through a talk on singletons. To begin with, here some code:

class AppSettings {

    private static AppSettings instance = new AppSettings();

    private Object state1;
    private Object state2;
    private Object state3;

    private AppSettings() {}

    public static AppSettings getInstance() {
        return instance;
    }

}

The speaker says that since instance is static, it is a global variable and whatever is accessible using instance will also have global state.

Can someone explain to me what global state means? I know that global state is accessible throughout the application, and can be changed by another objects which is bad. But how does declaring instance as static make it global?

Upvotes: 1

Views: 472

Answers (2)

Henry
Henry

Reputation: 43788

"global" is the wrong term for that. The variable instance is still only visible inside the AppSettings class. However the AppSettings instance referenced by it is made available to the outside world via the getInstance method.

Upvotes: 2

Hari Prasad
Hari Prasad

Reputation: 304

As there will be only one instance of the AppSettings object (as it is a static variable), the state member fields which can be accessed through this instance by any other object (Of course you need getters and setters for these members as they are private). Hence they can be used for maintaining global states

Upvotes: 1

Related Questions