Effective Java English Second Edition reading notes Item 4:attempting to enforce noninstantiability by making a class abstract does not work.

The class can be subclassed and the subclass instantiated. Futhermore,it misleads the user into thinking the class is designed for inheritance (inheritance). There is,however,a simple idiom to ensure noninstantiability. A default constructor is generated only if a class contains no explicit constructors,so a class can be made NONINSTANTIABL E by including a private constructor.

 Package noninstantiability; // noninstantiable Utility Class  Public class Utilityclass {    //Suppress default constructor for noninstantiability         Private  Utilityclass () {        thrownew  assertionerror ();    }    }

Effective Java English Second Edition reading notes Item 4:attempting to enforce noninstantiability by making a class abstract does not work.