Access modifiers in java

Ever been stumped by a fairly innocuous question during a job interview for a Java developer position? It happens to the best of us. The secret is to go over some of the most common questions ahead of time so that you are prepared with an answer to each of them. Keep in mind that interviewers tend to start with fairly broad topics and then drill down based on your answers. For that reason, this tutorial starts with the basics before moving onto more specialized areas. What is Java? Some developers list every popular language in their resume or CV, even if they have only seen it in passing or know just the basics. This first question is designed to quickly weed these people out. You do not need to cover the entire history of Java in your answer; something like this should suffice: “Java is a high-level, Object-oriented, programming language originally developed by Sun Microsystems and released in 1995. Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX. It’s currently maintained by the Oracle Corporation and is one of the most popular programming languages in the world.” What is the Java Virtual Machine? The question, “What is the Java Virtual Machine?” is a slightly more technical question, but one that goes to the heart of Java, because it is what makes the language platform-independent and supplies its garbage collection features. For this question, your answer might go as follows: “The Java Virtual Machine, or JVM, is a progra...

Overview Access Modifiers in Java provide a restriction on the scope of the class, instance variables, methods, and constructors. There are four types of Access modifiers in Java- Default, Private, Protected, and Public. They are different from each other due to the restricted scope they provide. If not specified, then Java uses the default modifier itself. Introduction to Access Modifiers in Java Let’s understand the Access Modifiers in Java with the help of real-life examples. There are many things that you want to share publicly or keep some things hidden. For example, The details of your salary are only known to your family members so this is a restriction. This restriction is similar to the Default modifier. The second aspect is your name which is known to all without any restriction. The public modifier follows the same concept. The protected modifier also used the public modifier concept but has little restriction on the scope (We will study this later in the article). You must be having some secrets that you don’t want to disclose to anyone, even with your family members. This is the same behavior as the private modifier. We will discuss all these different kinds of restrictions in this article. Let’s dive deep and understand the concept of Access Modifiers in Java. These are the four types of access modifiers in Java that are used to control the visibility/access of instance variables, constructors, and class methods: • private • protected • default • public Let's...

What are Access Modifiers? Have you ever wanted to define how people would access some of your properties? You would not want anyone using your underwear. However, your close friends and relatives can use your sweater and maybe your car. Similarly to how you set a level of access to your posessions, Java controls access, too. You want to define the access level for variables, methods and classes depending on which other classes you want accessing them. Java provides 4 levels of access modifiers. This means that you can modify access to a variable, method or a class in 4 ways. These 4 ways are private, public, protected and default. These access modifiers can be applied to fields, methods and classes (Classes are a special case, we will look at them at the end of this artice). Here is a quick overview 1 of what the Access Levels are for each Access Modifier: Access Modifiers Table Reference: Private Access Modifier Allows a variable or method to only be accessed in the class in which it was created. No other class beyond the class that created the variable or method can access it. This is closely similar to your internal organs. They are only accessible to the owner. To make a variable or method private, you simply append the private keyword before the variable or method type. Let us use private in a coding example. If a bank wants to provide an interest rate of 10% on it’s loans, it would make sure that the interest rate variable(let us suppose int int_rate;) would stay pr...

private can be accessed only by the class in which they're declared, the protected keyword allows access from sub-classes and members of the same package. By using the protected keyword, we make decisions about which methods and fields should be considered internals of a package or class hierarchy, and which are exposed to outside code. 3. Declaring protected Fields, Methods, and Constructors First, let's create a class named FirstClass containing a protected field, method, and constructor: public class FirstClass With this example, by using the protected keyword, we've granted access to these fields to classes in the same package as FirstClass and to sub-classes of FirstClass. Now, let's see how we can access protected fields by creating a new GenericClass declared in the same package as FirstClass: public class GenericClass As this calling class is in the same package as FirstClass, it's allowed to see and interact with all the protected fields, methods, and constructors. 4.2. From a Different Package Let's now try to interact with these fields from a class declared in a different package from FirstClass: public class SecondGenericClass As we can see, we get compilation errors: The constructor FirstClass(String) is not visible The method getName() from the type FirstClass is not visible The field FirstClass.name is not visible That's exactly what we were expecting by using the protected keyword. This is because SecondGenericClass is not in the same package as FirstCla...

The Modifier class provides static methods and constants to decode class and member access modifiers. The sets of modifiers are represented as integers with distinct bit positions representing different modifiers. The values for the constants representing the modifiers are taken from the tables in sections 4.1, 4.4, 4.5, and 4.7 of The Java™ Virtual Machine Specification. See Also: Class.getModifiers(), Member.getModifiers() Return a string describing the access modifier flags in the specified modifier. For example: public final synchronized strictfp The modifier names are returned in an order consistent with the suggested modifier orderings given in sections 8.1.1, 8.3.1, 8.4.3, 8.8.3, and 9.1.1 of The Java™ Language Specification. The full modifier ordering used by this method is: public protected private abstract static final transient volatile synchronized native strictfp interface The interface modifier discussed in this class is not a true modifier in the Java language and it appears after all other modifiers listed by this method. This method may return a string of modifiers that are not valid modifiers of a Java entity; in other words, no checking is done on the possible validity of the combination of modifiers represented by the input. Note that to perform such checking for a known kind of entity, such as a constructor or method, first AND the argument of toString with the appropriate mask from a method like constructorModifiers() or methodModifiers(). Parameters:...

@tennenrishin - well, that is what Nicolas said... and you are just repeating it now. What you originally said was that protected - and I quote - 'is a version of public restricted only to subclasses' which is not true by your own admission since protected also allows access through the whole package (ergo, it does not restrict access to subclasses.) I also agree with Nicolas in that the protected access mode in Java is idiotic. What happened is that Java conflated horizontal (lattice) and vertical access restriction qualifiers. Default scope is a horizontal/lattice restriction with the lattice being the package. Public is another horizontal restriction where the lattice is the whole world. Private and (C++) protected are vertical. It would have been better if we had a cross-cut access, say, protected-package for the rare cases where we actually needed it, leaving protected to be equivalent to the C++ version of protected. For example, if I have MyClass and I'm doing AnotherClass extends MyClass I will have access to all protected and public methods and properties from within AnotherClass. If I do MyClass myClass = new MyClass(); in AnotherClass somewhere - let's say the constructor - I will only have access to the public methods if it is in a different package. Note that if I do = new MyClass() ; it appears that I can access protected methods, but this kind of the same as extending it, but inline instead. Unfortunately, this answer is a gross oversimplification. Reality i...

You must have seen public, private and protected keywords while practising java programs, these are called access modifiers. An access modifier restricts the access of a class, constructor, data member and method in another class. In java we have four access modifiers: 1. default 2. private 3. protected 4. public 1. Default access modifier When we do not mention any access modifier, it is called default access modifier. The scope of this modifier is limited to the package only. This means that if we have a class with the default access modifier in a package, only those classes that are in this package can access this class. No other class outside this package can access this class. Similarly, if we have a default method or data member in a class, it would not be visible in the class of another package. Lets see an example to understand this: Default Access Modifier Example in Java To understand this example, you must have the knowledge of In this example we have two classes, Test class is trying to access the default method of Addition class, since class Test belongs to a different package, this program would throw compilation error, because the scope of default modifier is limited to the same package in which it is declared. Addition.java package abcpackage; public class Addition Output: 101 Lets see the scope of these access modifiers in tabular form: The scope of access modifiers in tabular form ------------+-------+---------+--------------+--------------+-------- | Cl...

I thought that it's such a common question, but I can't find anything which helps me. I'm relatively new to java and exercising for a job application. For that I've started writing a tool to transform data. (eg. read CSV, translate some columns and write it as SQL inserts to a file) If you're interested you find it here, I'll copy some code for my question: I've started with a Class which should read the CSV (and which will get more complex by enclosing some fields which should contain the seperator and so on). My IDE (IntellJ IDEA) suggested to use as strict access modifiers for my methods as possible. Why should I hide these methods (with private) from subclasses? package de.frederikvosberg.datatransformer; import java.io.BufferedReader; import java.io.Reader; import java.util.*; class CSVInput Another downside are the unit test. I would like to write separate tests for my methods. Especially the CSVInput::valuesFromLine method which will get more complex. My Unit test for this class is testing so much and I really don't want to have to many things in my head when developing. Any suggestions from experienced Java programmers? Thanks in advance Replies to comments Thank you for your comments. Let me answer to the comments here, for the sake of clarity. "Why should I hide these methods (with private) from subclasses?" Why do you keep your car keys away from your front door? For security purposes, but why does it affect security when I change the access modifier of the col...