What is the preferred Throwable to use in a private utility class constructor?

java coding-style throwable
Rob Hruska picture Rob Hruska · Dec 29, 2008 · Viewed 8.8k times · Source

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

Chris Jester-Young picture Chris Jester-Young · Dec 29, 2008

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

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