Question

Effective Java (Second Edition), Item 4, discusses using private constructors to enforce noninstantiability. Here’s the code sample from the book:

public final class UtilityClass {     private UtilityClass() {         throw new AssertionError();     } } 

However, AssertionError doesn’t seem like the right thing to throw. Nothing is being ‘asserted’, which is how the API defines the use of AssertionError.

Is there a different Throwable that’s typically in this situation? Does one usually just throw a general Exception with a message? Or is it common to write a custom Exception for this?

It’s pretty trivial, but more than anything I guess I’m just curious about it from a style and standards perspective.

Answer 1

There is an assertion: ‘I’m asserting that this constructor will never be called’. So, indeed, AssertionError is correct here.