# Hide Default Constructor In Utility Classes

# Properties

# Description

Utility classes are classes containing static properties only. Those classes should not be instantiated. A private constructor, which throws an IllegalStateException, is introduced to utility classes by this rule, if the following criteria are met:

• Only static methods and fields are present
• No constructor is declared
• No main method is defined
• The default constructor isn't invoked anywhere in the current workspace

This hides the default public constructor and thus prevents the instantiation of such a class.

# Benefits

Prevents the bad practice of unnecessary instatiation of utility classes.

# Requirement & Tags

# Code Changes

Pre

    public class UtilityClass {
        public static doSomething() {
            ...
            System.out.println("did something");
        }

        public static doSomethingElse() {
            ...
            System.out.println("did something else");
        }
    }

Post

    public class UtilityClass {
        private UtilityClass() {
            throw new IllegalStateException("Utility class");
        }

        public static doSomething() {
            ...
            System.out.println("did something");
        }

        public static doSomethingElse() {
            ...
            System.out.println("did something else");
        }
    }