Java — private constructor vs final and more

Question

Suppose there is a class with all of its constructors declared as private.

Eg.:

public class This {
    private This () { }

    public someMethod(          


        

Answer 1

From what I know the general use of a private constructor is to ensure that object construction is done via some other means, i.e. a static method. For example:

public class Something {

    private Something() { }

    public static Something createSomething() {
        Something ret = new Something();
        // configure ret in some specific way
        return ret;
    }

}

So a private constructor restricts how a class is instantiated (not how it is extended).

On the other hand, marking a class as final is used to explicitly say that a class cannot be extended. How it get's instantiated is a different matter entirely.

So while I'm not 100% if there is some way to extend a class that has all private constructors - the question is why do you want to do that? Having a private constructor and marking a class as final have two different purposes.