Access Modifiers

3 Key excerpts on "Access Modifiers"

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  eBook - ePub

  OCP Oracle Certified Professional Java SE 11 Programmer I Study Guide

  Exam 1Z0-815

  • Jeanne Boyarsky, Scott Selikoff(Authors)
  • 2019(Publication Date)
  • Sybex

    (Publisher)

  Line 20 calls a varargs method with two parameters. When the method gets called, it sees an array of size 2. Since indexes are 0 based, 22 is printed.

  Applying Access Modifiers

  You already saw that there are four Access Modifiers: public , private , protected , and default access. We are going to discuss them in order from most restrictive to least restrictive:

  • private : Only accessible within the same class
  • Default (package-private) access: private plus other classes in the same package
  • protected : Default access plus child classes
  • public : protected plus classes in the other packages

  We will explore the impact of these four levels of access on members of a class. As you learned in Chapter 1 , “Welcome to Java,” a member is an instance variable or instance method.

  Private Access

  Private access is easy. Only code in the same class can call private methods or access private fields.

  First, take a look at Figure 7.2

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  eBook - ePub

  100+ Solutions in Java - 2nd Edition

  Everything you need to know to develop Java applications (English Edition)

  • Dhruti Shah(Author)
  • 2023(Publication Date)
  • BPB Publications

    (Publisher)

  objCalc . Java allows to declare an object and initialize/allocate memory later. For example:

  Calculator objCalc;

  ObjCalc is a reference variable that does not point to any memory location yet. That is, it is null. Any attempt to use this variable at this point will result in an error. To use this variable, it must be initialized first. For example:

  objCalc = new Calculator();

  Now, memory is allocated to the object, and its reference is stored in objCalc variable. Therefore, it can be used to access the members of Calculator class.

  3.2 Access specifiers

  In Java, apart from encapsulating the data members and methods in a class, further restriction on access can be provided by using access specifiers. Java provides the public, private, and protected access specifiers that provide different levels of visibility to a class, field, and method. When no access specifier is mentioned for a class member, the default accessibility is package or default.

  The access specifiers supported by Java are:

  • public: The public access specifier makes a field, method, or class visible to any class in a Java application within the same package or another package. Hence, it is the least restrictive of all access specifiers.
    With the introduction to JPMS in JDK 9, the meaning of the public has been elevated to the module level as well based on the declaration of exports in the module-info.java file. With modules, the public keyword can be applied as:
    • Public only within the module : The public classes of a package within a module that are not exported using exports keyword, will be accessible only within the module. For example: module com.ModuleA{ }
      Here, since no package is exported, all classes are public only within ModuleA .
    • Public to everyone : The public classes of a package within a module that is exported using exports keyword will be accessible to classes of other modules. For example: module com.ModuleA{ exports pkg1.test; } module com.ModuleB{ requires com.ModuleA // reading ModuleA }
      Here, pkg1 is being exported so its public class is can be accessed by other modules.
    • Public only to a specific module

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  eBook - ePub

  Pocket Primer

  • Oswald Campesato(Author)
  • 2022(Publication Date)
  • Mercury Learning and Information

    (Publisher)

  String is initialized to null, and so forth.

  The keyword public exposes properties and methods, whereas the keyword private restricts access to the class itself. The keyword protected limits access to the internals of a class to its subclasses as well as the class itself.

  Here are some examples of using the private and public keywords:

  private String fname = "Dave"; public String getName() { return fname; } public void setName(String newName) { fname = newName; }

  The setters and getters in a class are also called accessors and mutators , respectively.

  THE SCOPE OF JAVA VARIABLES

  Java supports reference data types that are created during instantiation of a class.

  A reference variable can refer to any object of the declared type or any compatible type (such as a subclass).

  There are three types of scopes for variables in Java : local , instance , and static . Local variables are declared inside methods, constructors, or blocks. Instance variables are declared in a class, and they do not appear inside any methods, constructors or blocks. Listing 3.1 displays the content of JavaVars.java

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