Private Public Java

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Private Public Java
Difference between public, private, protected and default in Java

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In the article, we have covered the differences between public, private, protected and no modifier in Java in detail.
In short, following image summarizes the differences:
First and important difference is the accessibility i.e. anything public is accessible to anywhere , anything private is only accessible in the class they are declared , anything protected is accessible outside the package but only to child classes and default is accessible only inside the package .
Another difference between public and private modifier is that of Encapculation . Public modifier provides lowest level of Encapculation and Private modifier provides higher level of Encapsulation in Java.
Another difference is that you can use public modifier with top level class but you cannot make a top level class private in java.You can make inner class private.
Another difference is that default is package level accessibility i.e. if you don't provide any access modifier to a class, method or variable then Java by default make them accessible inside the package .
Another difference between protected and default modifier is that protected modifier provides more accessibility than default modifier.You can access a protected member outside the package , but only inside sub classes .
That's all about difference between public,private,protected and no modifier in Java.
To understand this deeply, we will go through important terms like class, subclass, package and others and then, understand each access specifier with code examples.
A class defines the characteristics and behaviour of an object.For example,if you create a gaming application,each game that a user can play from the aplication can be considered as an object of the Games class.Each game has common characteristics,such as the number of players,game category and score.These characteristics are known as member variables and behavior is specified by methods . A class defines the member variables and methods of objects that share common characteristics. Further,all the games have common methods , such as calculating score,starting the game and displaying game instructions.
A Java subclass is a class which inherits a method from a superclass(the class from which subclass is derived).To create a subclass of another class, use the extends clause in your class declaration.As a subclass, your class inherits member variables and methods from its superclass.
An object is an instance of a class and has a unique identity.The identity of an object distinguishes it from other objects.Classes and objects are closely linked to each other. Declaring an object creates a variable that will hold the reference to the object.Īn this, new operator is used, which allocates memory to an object.
Syntax :
A package is a collection of classes. A package provides the space essentially used to organize classes that are related to each other.You can create multiple packages to organize multiple categories of classes as per the requirement.A class can belong only to one package.For example, a package named Game can be used to create and store a class named Game1 .This will ensure that the Game1 class does not conflict with any that has the same name and is stored somewhere else.
In Java, there are number of Access Modifiers to control the access of class members. The various types of access modifiers in Java are:
The members of a class that are preceded with the public modifier are accessible by the classes present within the package or outside the package .
You can access a public class,data member or method within the class in which they are defined, from the classes defined in the same package or outside the package .The following code snippet shows how to declare a data member of a class as public :
The following code shows how the public modifier can be implementerd in the ClassicGame class for the start variable:
In the preceeding code, the start variable has been specified with the public modifier. The start variable can be accessed anywhere in the class ClassicGame class. It is also accessible in the package in which the ClassicGame class is created, or in a package that is different from the one where the ClassicGame class exists.
The private modifier allows a class to hide its member variables and member methods from other classes.Therefore, the private members of a class are not visible outside a class.They are visible only to the methods of the same class.Therefore, the data remains hidden and cannot be altered by any method other than the member methods of the class.If a variable or methods is declared private , it can be accessed only within its enclosing class.A top class cannot be declared private in Java.However, an inner class can be declared private .The following code snippet shows how to declare a private data member of a class:
The following code shows how the private modifier can be implemented in the ClassicGame class for the score variable:
In the preceeding code, the score variable has been specified with the private modifier.The score variable can be accessed anywhere in the ClassicGame class, but it is not accessible to other classes.
The members of a class that are preceded with the protected modifier are accessible to all the classes within the package and by the subclasses outside the package .The protected modifier becomes important while implementing inheritance.The following statement shows how to declare a protected data member of a class:
In the preceeding code,the score variable is declared as protected .It can therefore be accessed within the ClassicGame class from the classes that will inherit the from ClassicGame class.It can also be accessed within the classes of the package that contains the ClassicGame class.
This is also known as default modifier.If you do not specify any of the preceeding modifiers, the scope of data members and methods is default or friendly .A class, variable or a method with a friendly access can be accessed only by the classes that belong to the package in which they are present.
With this , revisit the differences we presented at the beginning. It will be much more clear. Enjoy.
The problem is to find out the smallest missing positive integer given an unsorted integer array. We can solve this problem in linear time O(N) and in constant time O(1) using a greedy approach with hash map.
We have discussed the different word representations such as distributional representation, clustering based representation and distributed representation with several sub-types for each representation.


Written by Jeremy Grifski in Code Last Updated May 26, 2020
public static void main ( String [] args ) {
System. out . println ( "Hello, World!" ) ;
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
public static void main ( String [] args ) {
System. out . println ( "Hello, World!" ) ;
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
public static void main ( String [] args ) {
private static void printHelloWorld () {
System. out . println ( "Hello, World!" ) ;
public class HelloWorld {
public static void main(String[] args) {
printHelloWorld();
}

private static void printHelloWorld() {
System.out.println("Hello, World!");
}
}
public static void main ( String [] args ) {
HelloWorld. printHelloWorld () ; // ERROR
public class CallPrivateMethod {
public static void main(String[] args) {
HelloWorld.printHelloWorld(); // ERROR
}
}
this . wipers = new boolean [ 2 ] ;
private void turnOnWiper ( int index ) {
for ( int i = 0 ; i < this . wipers . length ; i++ ) {
public class Car {
private boolean[] wipers;

public Car() {
this.wipers = new boolean[2];
}

private void turnOnWiper(int index) {
this.wipers[index] = true;
}

public void turnOnWipers() {
for (int i = 0; i < this.wipers.length; i++) {
this.turnOnWiper(i);
}
}
}
public static void main ( String [] args ) {
car. turnOnWipers () ; // Turns on wipers!
car. turnOnWiper ( 1 ) ; // Compilation ERROR
car. wipers [ 0 ] = false ; // Compilation ERROR
public class CarBuilder {
public static void main(String[] args) {
Car car = new Car();
car.turnOnWipers(); // Turns on wipers!
car.turnOnWiper(1); // Compilation ERROR
car.wipers[0] = false; // Compilation ERROR
}
}

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As I was writing my first semester of teaching reflection , I got the idea to kick off a series of student questions called Coding Tangents. In this series, I’ll be tackling student questions with clear, easy-to-follow explanations that demystify common programming language syntax. In particular, I’d like to tackle the difference between public and private in Java today.
Often times when we teach Java, we’re stuck leaving a lot of the syntax as a mechanical process. In other words, we tell students that keywords like public , static , and private will be explained to them later. In the meantime, they just have to trust that we will actually explain those concepts later.
One of these pieces of syntax that almost always gets left for a later discussion is private vs. public . These keywords are known as access modifiers, and we’ll dig into them in this article.
But first, let’s take a look at an example of some code that is almost certain to raise some questions about access modifiers:
In order to teach Java, we’re often stuck introducing the language using these horrible five lines of code. After all, this is the bare minimum required to get a Java program running.
As a result, we’re often forced to tell students something along the lines of:
Don’t worry about the outer four lines. Just place whatever code you want to execute in the middle block.
Of course, this line of reasoning leaves a lot to be desired if you’re a new student. For example, what do any of those four outer lines do? What’s public ? How about static , String[] , or System.out.println ?
 Luckily, I’m hear to cover the access modifier part today.
At this point, let’s talk about access modifiers at a high level.
In Java, access modifiers are a way to help us from stepping on our own feet. In general, they’re used to set some level of access to a class, method, or variable.
For example, if we want to model something from the real world (say a car), there are certain aspects of that object we probably don’t want to expose to the public (say individual control over the wiper blades). Perhaps under the hood, the wipers are individually controlled, but we’ve built our system such that the switch given to the user has encapsulated that behavior. In other words, both wipers move together as expected. 
Had we chosen to expose individual control over each wiper, we may find that many users accidentally break the wiper functionality. After all, if the wipers aren’t perfectly synced, they may smash into each other.
That’s the high level idea behind access modifiers. We use them to expose or hide certain functionality to improve the overall user experience. 
At this point, a lot of students will start thinking that access modifiers are some way to make code more secure from hackers. While this is largely untrue, there is some merit in the argument. Sure, nothing is stopping someone from using a feature like reflection to access private fields and methods. That said, access modifiers can help protect the average user from corrupting an object’s state.
Think about the windshield wiper example. When we turn on our wipers, we expect both of them to move at the same speed. Without restricted access, we could change the default speed of one of the wipers. Then, the next time we’d go to turn on the wipers… BAM! To avoid that problem, we encapsulate (or hide) the fact that we have two individual wipers in a single exposed (public) method.
Encapsulation is the art of reducing a complex state down to a set of exposed behaviors. If I were to ask you to throw a ball, you certainly wouldn’t start by requesting a set of matrix transformations for the rotation of your arm. You’d just throw the ball. That’s the idea behind encapsulation (and abstraction). 
In this example, we can use access modifiers to specify which behaviors are exposed. For example, we’d probably want to allow users to access the throw command but maybe not the rotateArm or pickUpBall commands. 
Now that we’ve tackled some of the misconceptions, let’s get into the syntax.
In Java, there are actually four access modifiers: public , private , package-private (default), and protected . Each keyword offers a level of code access given by the following table:
In other words, we can rank the keywords in order of least accessibility:
For the duration of this tutorial, I will not be exploring the package-private or protected keywords as they’re a bit more nuanced, but I figured they were important to mention.
Using the ball throwing example from before, let’s try to figure out which access modifier would be appropriate in various situations:
Notice how all the high level actions are public and the lower level actions are private. That’s because we don’t necessarily want to expose the lower level actions to the public. But, why not? Let’s take a look at another example.
Let’s say that the high level functions rely on some underlying state of the system. For instance, throwing a ball relies on knowing information like the strength of gravity and the properties of the ball. If someone were somehow able to access the lower level actions, they could potentially manipulate these basic assumptions of the world.
What would happen if we were able to access actions like setGravity or setBall ? How would our high level actions like throw or catch change?
Using the setGravity command, I could tell you that gravity is actually twice as strong as you think it is before telling you to throw the ball. At that point, you’d update your model of the world before significantly increasing the force of your throw to accommodate for the change in gravity. However, in reality, gravity hasn’t actually changed, so instead you overthrow the ball.
This scenario is often what happens when we expose lower level functionalities that don’t trigger automatic updates of dependent properties. In many cases, systems are very complicated, and changing one underlying parameter results in the failure of the system. As a result, we try to encapsulate functionality to cover all our bases. 
Up until this point, we’ve been talking mostly about the philosophy of access modifiers, but what are the real world consequences and how do we actually use them? To help clarify those questions, let’s take a moment to write some of our own classes which try to demonstrate the practical differences between public and private .
Now that we’ve seen some high level explanations, let’s dig back into our Hello World example.
Here we can see that we use the public keyword twice: once for the class and again for the main method. In other words, we’ve chosen to expose both the HelloWorld class and the main method to the public. 
To make things a little more interesting, let’s wrap the print in its own private method:
If we try to run this solution, we’ll notice that the behavior hasn’t changed at all. That’s because private methods can be used in their own class. Outside HelloWorld , however, no one knows printHelloWorld() even exists. In fact, we could try to call the method directly from another class in the same folder, and we’d find ourselves with an error:
As we can see, we’ve hidden away the printing functionality, so that it can only be used by the HelloWorld class. If for some reason we made the printHelloWorld() method public, we could run it just fine.
Now, let’s take this concept a step further by actually implementing the windshield wipers in Java (at least at a high level). To start, we’ll make a car class that has a private method for one wiper and a public method for both wipers:
Here, we’ve created a Car class that stores a private array of wiper states. For each wiper, their state is either on ( true ) or off ( false ). To turn a wiper on, we’ve written a private method that lets you turn on a wiper by its index. Then, we bring all that together with a public method that iterates through all the wipers and turns them all on.
Now, ignoring the realistic problem here which is that the wipers are being turned on in series, not parallel, we have a pretty solid solution. If someone were to instantiate a Car, they would only be able to turn on all the wipers at once.
Fun fact: the user doesn’t even know how the wipers are implemented, so we have full control to change the underlying architecture at any time. Of course, we still have to provide the same functionality, but how we get there is up to us. In other words, we could potentially change the wiper array to store integers. Then, for each wiper, the integer would correlate to speed.
Now, why don’t you try expanding the class yourself. For example, I recommend adding a method to turn off the wipers. You may want to then write a new private method for turning off individual wipers, or you might find it makes more sense to refactor the turnOnWiper method to take a boolean as well. Since the user never sees those methods, you have full control over the underlying implementation. Happy coding!
Hopefully this helps you understand the difference between the private and public keywords, and why we use them. If not, I’m open to any feedback and questions you may have. Feel free to use the comments below to start a bit of a dialogue. And if this helped you out at all, share it with your friends. I always appreciate the support!
As a lifelong learner and aspiring teacher, I find that not all subjects carry the same weight. As a result, some topics can fall through the cracks due to time constraints or other commitments. Personally, I find these lost artifacts to be quite fun to discuss. That’s why I’ve decided to launch a whole series to do just that. Welcome to Coding Tangents, a collection of articles that tackle the edge case topics of software development.
In this series, I’ll be tackling topics that I feel many of my own students have been curious about but never really got the chance to explore. In many cases, these are subjects that I think deserve more exposure in the classroom. For instance, did you ever receive a formal explanation of access modifiers? How about package management? Version control?
In some cases, students are forced to learn these subjects on their own. Naturally, this forms a breeding ground for misconceptions which are made popular in online forums like Stack Overflow and Reddit. With this series, I’m hoping to get back to the basics where these subjects can be tackled in their entirety.
Jeremy grew up in a small town where he enjoyed playing soccer and video games, practicing taekwondo, and trading Pokémon cards. Once out of the nest, he pursued a Bachelors in Computer Engineering with a minor in Game Design. After college, he spent about two years w
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