Can we override a constructor in Java and can a constructor be private?

Question

I would appreciate an explanation for these questions:

1. Can we Override a constructor in Java?
2. Can a Constructor be private?<

Answer 1

No, you can't override a constructor. They're not inherited. However, each subclass constructor has to chain either to another constructor within the subclass or to a constructor in the superclass. So for example:

public class Superclass
{
    public Superclass(int x) {}

    public Superclass(String y) {}
}

public class Subclass extends Superclass
{
    public Subclass()
    {
        super(5); // chain to Superclass(int) constructor
    }
}

The implication of constructors not being inherited is that you can't do this:

// Invalid
Subclass x = new Subclass("hello");

As for your second question, yes, a constructor can be private. It can still be called within the class, or any enclosing class. This is common for things like singletons:

public class Singleton
{
    private static final Singleton instance = new Singleton();

    private Singleton()
    {
        // Prevent instantiation from the outside world (assuming this isn't
        // a nested class)
    }

    public static Singleton getInstance() {
        return instance;
    }
}

Private constructors are also used to prevent any instantiation, if you have a utility class which just has static methods.