What exactly is a helper method?

A helper method is used to perform a particular repetitive task common across multiple classes. This keeps us from repeating the same piece of code in different classes again n again. Whereas the class-specific methods define its behaviour, the helper methods assist in that process. You can think of Integer.parseInt() as a helper method that we have been using across multiple classes irrespective of their independent behaviour.

Helper methods are often declared as public static so they can be invoked with the class name like Classname.method(). For example, below I have created a HelperMethods class which consists of helper methods that I can use across multiple classes. I have created another Test class and used the HelperMethods.preMr() helper method to prepend "Mr." to the name. I can create more classes if I want to and use the same helper methods with them. One can even build a custom library of functions that can be used in any project due to its generic nature.

public class HelperMethods {
    public static String preMr(String name) {
        return "Mr. " + name;
    }
    public static String preMs(String name) {
        return "Ms. " + name;
    }
    public static String preDr(String name) {
        return "Dr. " + name;
    }
}

public class Test {
    public static void main(String[] args) {
        String name = "Manav";
        System.out.println(HelperMethods.preMr(name)); // Mr. Manav
    }
}