Private Method

Private Method
class MyClass {
#privateMethod() {
//...
}
}
class MyClass {
static #privateStaticMethod() {
//...
}
}
class MyClass {
#field;
get #myField() {
return #field;
}
set #myField(value){
#field = value;
}
}
class Person {
#firstName;
#lastName;
constructor (firstName, lastName) {
this .#firstName = firstName;
this .#lastName = lastName;
}
getFullName(format = true ) {
return format ? this .#firstLast() : this .#lastFirst();
}

#firstLast() {
return ` ${ this .#firstName} ${ this .#lastName} ` ;
}
#lastFirst() {
return ` ${ this .#lastName} , ${ this .#firstName} ` ;
}
}

let person = new Person( 'John' , 'Doe' );
console .log(person.getFullName());
class Person {
#firstName;
#lastName;
constructor (firstName, lastName) {
this .#firstName = Person.#validate(firstName);
this .#lastName = Person.#validate(lastName);
}
getFullName(format = true ) {
return format ? this .#firstLast() : this .#lastFirst();
}
static #validate(name) {
if ( typeof name === 'string' ) {
let str = name.trim();
if (str.length === 3 ) {
return str;
}
}
throw 'The name must be a string with at least 3 characters' ;
}

#firstLast() {
return ` ${ this .#firstName} ${ this .#lastName} ` ;
}
#lastFirst() {
return ` ${ this .#lastName} , ${ this .#firstName} ` ;
}
}

let person = new Person( 'John' , 'Doe' );
console .log(person.getFullName());
The JavaScript Tutorial website helps you learn JavaScript programming from scratch quickly and effectively.
Home » JavaScript Tutorial » JavaScript Private Methods
Summary : in this tutorial, you’ll learn about JavaScript private methods including private instance methods, private static methods, and private getter/setter.
By default, members of a class are public. ES2020 introduced the private members that include private fields and methods.
To make a public method private, you prefix its name with a hash # . JavaScript allows you to define private methods for instance methods, static methods , and getter/setters .
The following shows the syntax of defining a private instance method:
In this syntax, the #privateMethod is a private instance method. It can only be called inside the MyClass . In other words, it cannot be called from outside the class or in the subclasses of the MyClass .
To call the #privateMethod inside the MyClass , you use the this keyword as follows:
The following illustrates the syntax of defining a private static method:
To call the #privateStaticMethod() inside the MyClass , you use the class name instead of the this keyword:
The following shows the syntax of the private getters/setters:
In this example, the #myField is the private getter and setter that provide access to the private field #field .
In practice, you use private methods to minimize the number of methods that the object exposes.
As a rule of thumb, you should make all class methods private by default first. And then you make a method public whenever the object needs to use that method to interact with other objects.
Let’s take some examples of using private methods
The following illustrates how to define the Person class with private instance methods:
First, define two private fields #firstName and #lastName in the Person class body.
Second, define the private methods #firstLast() and #lastFirst() . These methods return the full name in different formats.
Third, define the public instance method getFullName() that returns a person’s full name. The getFullName() method calls the private method #firstLast() and #lastFirst() to return the full name.
Finally, create a new person object and output the full name to the console.
The following adds the #validate() private static method to the Person class:
First, define the static method #validate() that returns a value if it is a string with at least three characters. The method raises an exception otherwise.
Second, call the #validate() private static method in the constructor to validate the firstName and lastName arguments before assigning them to the corresponding private attributes.
Copyright © 2022 by JavaScript Tutorial Website. All Right Reserved.

Java-SE1728: Access Modifier (priva...
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Private methods in Java have a private access modifier which means they have limited access to the defining class and are not accessible in the child class in inheritance; that is why they are not eligible for overriding.
However, a method can be created in the child class and could be accessed in the parent class. This tutorial demonstrates how to create and use private methods in Java.
As mentioned above, private methods are only accessible in the defining class; we consider the points below for the private methods.
Let’s try to create and use private methods in Java. See example:
The code above creates a private method and calls it in the same class and also a public method to call it in the parent class; the output will be:
If we change the public method to private in the child class, it will throw an exception. See example:
We cannot access the print method from the child class. See output:
Copyright © 2020. All right reserved

Private Methods can only be used inside the class. To set private methods, use the private access specifier.
Private access specifier allows a class to hide its member variables and member functions from other functions and objects. Only functions of the same class can access its private members. Even an instance of a class cannot access its private members.
In the above example, we cannot call the private method displayOne(). If we try to call, then an error would be visible.
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I understand it is a very basic concept in the oops. But still I cannot get my head around. I understood why member variables are private, so class user cannot abuse it by setting up invalid values.
But how can this apply to the methods ?
Trending sort is based off of the default sorting method — by highest score — but it boosts votes that have happened recently, helping to surface more up-to-date answers.
It falls back to sorting by highest score if no posts are trending.
Lot of good answers, but maybe one more from a self-taught Java programmer as I went through all that by myself with a lot of pain ;)
Think about a Class as something seen from the outside, not as something you see internally . If you look at a Class from the outside, what you see?
Taking the clock as an example again, a clock can give you info about the current time and it can be set up to show the right time .
So looking at things from the outside, a clock is a machine that can do those two things; public methods we call them .
But we as constructors of this clock we know that before any time operation we have to switch from 23 to 11 on our display (it's that kind of clock), so we have to rearrange things internally a bit to do so. Changing from 23 to 11 works just fine for us in both cases - setting the clock and showing the current time - but we do it "on the side" as the user doesn't have to know about all that complicated math. These are private methods!
So our Clock Class could have two public methods ( showTime and setTime ) which are all that the user wants to see, and a private method ( recountTime ) that provides functionality for these public methods and are something that the user doesn't want to see.
So on the one hand, you should keep in mind that private is what won't be reimplemented and accessed by future programmers using your code (as was pointed at in the answers above). But private also means things done on the side, so the user don't see it . That's why we call the public methods a public interface - it's all the user will see from the outside.
For me it is helpful (I'm self-taught, so maybe it's not a very popular methodology...) to write down everything the users (real users and other Classes) will do with my Class (public interface with just public methods' signatures), then to write the signatures of private methods that I-the-implementer will use to accomplish the public goals that promised to provide to my users and then just fulfill it with code.
It can be helpful to keep in mind that the old C rule is still valid (as was expressed in 97 Things Every Programmer Should Know ): a function/method should be just a few lines long, really!!
Private methods are useful for breaking tasks up into smaller parts, or for preventing duplication of code which is needed often by other methods in a class, but should not be called outside of that class.
Methods are (also) used to structure code, and I don't want the internal structure of my implementation to leak out through the interface. Often I have a method which to the outside seems to do a single task, but actually has to perform a couple of smaller tasks. In such cases I make one small private method for each of the subtasks and call them from the publicly visible method.
The whole issue is other people can't behave. Let me explain.
In a perfect world you would not gain anything by "hiding" stuff from others, you could make all your methods public, tell them which ones to use, and go have fun. But sooner or later someone will rely on a method you wrote, let's say a method that's meant to be internal, just for you, some low level stuff that you expected to be able to change anytime - alas, now you can't, because someone else is relying on it . You change it, and something else breaks. For no visible reason. Because someone didn't use your class as you advised, someone called your inner methods and you improved something in your code.
Hiding methods is reserving the right to change them.
Public interfaces should not change, unless it's a major step, like a new version. But the inside world is your playground. No matter how you get things done, as long as you deliver the expected output, it's no one else's business.
So the biggest reason to make methods private is your own freedom. Some will say it's for "security" reasons, but nowadays your code is often visible/editable so obviously we're not talking about access levels here. It's there, but it's not recommended to use. That's what private (and protected ) means.
For exactly the same reason - some methods are only intended for use inside the class, and use by non-class objects would be abuse. Think of methods that increment and decrement an object count for the class - these should only be called from a class's constructors or destructor, and so should be private.
Well in some cases you want only that specific class to use a method, and protect it from being used by any other class.
Just an example to show how it can be used:
You have a class Clock, it runs and runs keeping track of the time and date. You can get the time or date from it trough public methods. But the clock has to be right. so you can't adjust the time or date from outside of the class. But the clock itself needs to be able to adjust the time (daylights saving time for example)
In this case the Clock will have a private method to adjust the time.
Then you also have an additional pro, which is structuring the code . You can split up your code in smaller private methods which structure the code but prevent them from being used outside your class.
Methods that are private can only be called by methods within the same class or within the same "module". Methods are not commonly made private; usually they're made protected so that children can call them, or public so that other code can call them.
Having all other answers in mind. It is worth to remember that private method are only a tip for a programmer in many languages. In most cases it is still possible to use private method. For example by creating an object that inherits from object with private method and overrides its method with new public method.
In some modern highly object oriented languages private methods exist only by convention. Method with '_' on beginning is considere to be private.
Private methods are those methods which can’t be accessed in other class except the class in which they are declared. We can perform the functionality only within the class in which they are declared.
But in C++ they can also access by Friend class.
Public methods are those methods which can be accessed in any class.
Protected methods are those which can be accessed in derived class too.
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