helper_and_utility_class

Helper Class

• https://www.baeldung.com/java-helper-vs-utility-classes
• can contain instance as well as static methods
• It can be stateful

class MyHelperClass {
    public double discount;
 
    public MyHelperClass(double discount) {
        if (discount > 0 && discount < 1) {
            this.discount = discount;
        }
    }
 
    public double discountedPrice(double price) {
        return price - (price * discount);
    }
}

Utility Class

• only contain static methods
• We declare class as final
• We do not mark the class abstract since it will indicate that someone will want to extend it
• We do not use interface as utility class since it can be implemented, and it is not possible to have final interface
• It is sometimes stateless without static fields
• It cannot be instantiated, hence we write a private constructor
• generally named plural
• Examples:
  • Arrays
  • Collections
  • Objects
  • Streams
  • Collectors
  • Comparators (from Spring framework, not java.util)
  • Executors
• https://stackoverflow.com/questions/32375149/is-it-mandatory-utility-class-should-be-final-and-private-constructor

public final class StringUtils {
 
    private StringUtils() {}
 
    public static String toUpperCase(String str) {
        return str.toUpperCase();
    }
}