Can java have Protected or Private Constructor

Yes, you can have a protected or private constructor. As you mentioned the singleton pattern is a common example where a constructor is declared as being private. Basically you use a private constructor to enforce noninstantiability. You use a protected constructor to prevent instantiation outside of the package.

YoGeea at 2007-7-14 16:57:49 >

Hi,

Yes, We can declare constructor as private/public/protected also.

Having only private constructors means that you can't instantiate the class from outside the class (although instances could still be created from within the class - more about this later). However, when you instantiate a class, you must first initialize all superclasses of that class by invoking their constructors. If one of the superclasses has only private constructors declared, we have a problem. We can't invoke the superclass' constructor which means that we can't instantiate our object. Because of this, we've essentially made a class that can't be extended.

example:

class TheWorld

{

private static TheWorld _instance = null;

private TheWorld() {}

public static TheWorld instance()

{

if ( _instance == null )

{

_instance = new TheWorld();

}

return _instance;

}

public void spin() {...}

}

public class WorldUser

{

public static void main(String[] args)

{

TheWorld.instance().spin();

}

}

Java@kondala at 2007-7-14 16:57:49 >