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

Question

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

public fi         


        

Answer 1

When the code requires the inclusion of the JUnit as a dependency such as within the maven test scope test, then go straight to Assertion.fail() method and benefit from significant improvement in clarity.

public final class UtilityClass {
    private UtilityClass() {
        fail("The UtilityClass methods should be accessed statically");
    }
}

When outside the test scope, you could use something like the following, which would require a static import to use like above. import static pkg.Error.fail;

public class Error {
    private static final Logger LOG = LoggerFactory.getLogger(Error.class);
    public static void fail(final String message) {
        LOG.error(message);
        throw new AssertionError(message);
        // or use your preferred exception 
        // e.g InstantiationException
    }
}

Which the following usage.

public class UtilityClassTwo {
    private UtilityClassTwo() {
        Error.fail("The UtilityClass methods should be accessed statically");
    }
}

In its most idiomatic form, they all boil down to this:

public class UtilityClassThree {
    private UtilityClassThree() {
        assert false : "The UtilityClass methods should be accessed statically";
    }
}

One of the built in exceptions, UnsupportedOperationException can be thrown to indicate that 'the requested operation is not supported'.

 private Constructor() {
    throw new UnsupportedOperationException(
            "Do not instantiate this class, use statically.");
}