EJ-4 Enforce Noninstantiability with a Private Constructor

Ref: Effective Java by Joshua Bloch

Occasionally you'll want to write a class that is just a grouping of static methods and static fields like java.util.Collections. Such utility classes were not designed to be instantiated, an instance would be nonsensical. A class can be made noninstantiable by including a private constructor.

	// Noninstantiable utility class
	public class UtilityClass {
	// Suppress default constructor for noninstantiability
	private UtilityClass() {
	throw new AssertionError();
	}
	... // Remainder omitted
	}

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