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Chapter 8: Problem 2

Explain the notion of package access in Java. Explain the negative aspects of package access.

Short Answer

Expert verified
Package access in Java allows classes in the same package to access each other's members without any modifiers. Negatives include limited reusability, higher inter-package coupling, and lack of detailed access control within the package.

Step by step solution

01

Define Package Access

In Java, when a class or a class member is declared with no access modifier, it is given package access. This means that the class or member can be accessed by any other class in the same package, but not by classes in different packages.
02

Understand the Scope of Package Access

Package access is more restrictive than public access but less restrictive than protected or private access. This level of access control is often used when classes and members are intended to be used internally within a package.
03

Discuss the Negative Aspects of Package Access

The main negative aspects of package access are 1) limited reusability, since classes outside the package cannot access these package-private members, 2) increased inter-package coupling, which can lead to maintenance issues if the package's internal structure needs to be changed, and 3) lack of fine-grained access control within the package, as all classes in a package have equal access to each other's package access members.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Java Access Modifiers
In Java, access modifiers are the backbone of one of the fundamental object-oriented principles: encapsulation. Access modifiers determine the visibility and accessibility of classes, methods, and other members. There are four types of access modifiers in Java:
  • Public: These members are accessible from any other class in any package.
  • Protected: Members are accessible within their own package and by subclasses, which may even be in different packages.
  • Default (also known as package-private): Accessible only within the package where they are declared.
  • Private: Accessible only within the class where they are declared.

Choosing the right access modifier is crucial for security and proper organization of code. It enables other parts of the program to interact with the protected data only through methods that are safely exposed and guards against unauthorized access and modifications.
Package-Private Accessibility
Package-private accessibility is Java's default access level when no modifier is explicitly specified. A package-private class or member is accessible from other classes only within the same package. This level of access serves a specific purpose: to create a closely-knit group of related classes that can freely interact with each other, but remain hidden from the outside.

Package-private access can be seen as a compromise between encapsulation and convenience. It allows for cleaner internals where classes within a package work as a unit. However, from an improvement perspective, package-private access may lead to difficulty in understanding the relationships and interactions between classes for someone who is new to the codebase, as the intended access policies are not explicitly stated.
Java Encapsulation
Java encapsulation is a principle that encourages the safekeeping of the internal state and functionality of an object. It is about bundling data (variables) and methods that manipulate the data into one unit, the class, and restricting access to the inner workings of that class.

Encapsulation is achieved by using access modifiers to hide the class members, only allowing controlled access through methods known as 'getters' and 'setters.' This design approach safeguards against the accidental modification of data and supports maintainability and flexibility in a codebase. Encapsulation is often referred to as data hiding, but it's more about creating a protective barrier around the data.
Java Package Structure
The Java package structure provides organization and namespace management for classes and interfaces. Packages are used to group related classes and define a unique namespace, preventing name clashes between similarly named classes from different developers or modules.

A well-structured package can also indicate the functionality, level, or layer within an application making the codebase more navigable and maintainable. When developing software, it's beneficial to follow naming conventions and logical structuring to create intuitive and easy-to-understand package hierarchies. Understanding the package structure is essential when working with access levels, as it influences how classes are compiled and accessed within an application.

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Most popular questions from this chapter

Create class Date with the following capabilities: a) Output the date in multiple formats, such as MM/DD/YTYY June 14,1992 DDD YYYY b) Use overloaded constructors to create Date objects initialized with dates of the formats in part (a). In the first case the constructor should receive three integer values. In the second case it should receive a String and two integer values. In the third case it should receive two integer values, the first of which represents the day number in the year. \([\text {Hint: }\) To convert the String representation of the month to a numeric value, compare Strings using the equals method. For example, if \(s 1\) and \(s 2\) are Strings, the method call \(s 1 .\) equals \((s 2)\) returns true if the Strings are identical and otherwise returns false. \(]\)

Fill in the blanks in each of the following statements: a) When compiling a class in a package, the javac command-line option _______ specifies where to store the package and causes the compiler to create the package's directories if they do not exist. b) String class static method ______ is similar to method System.out.printf, but returns a formatted String rather than displaying a String in a command window. c) If a method contains a local variable with the same name as one of its class's fields, the local variable ______ the field in that method's scope. d) The ______ method is called by the garbage collector just before it reclaims an object's memory. e) \(A(n)\) ______ declaration specifies one class to import. f) If a class declares constructors, the compiler will not create a(n) _______. g) An object's _______ method is called implicitly when an object appears in code where a String is needed. h) Get methods are commonly called _______ or ________. i) \(A(n)\) _______ method tests whether a condition is true or false. j) For every enum, the compiler generates a static method called _______ that returns an array of the enum's constants in the order in which they were declared. k) Composition is sometimes referred to as a(n) ________ relationship. l) \(A(n)\) _______ declaration contains a comma-separated list of constants. m) \(A(n)\) ______ variable represents classwide information that's shared by all the objects of the class. n) \(A(n)\) _____ declaration imports one static member. o) The ______ states that code should be granted only the amount of privilege and access that it needs to accomplish its designated task. p) Keyword _______ specifies that a variable is not modifiable. q) There can be only one ______ in a Java source-code file, and it must precede all other declarations and statements in the file. r) \(A(n)\) ______ declaration imports only the classes that the program uses from a particular package. s) The compiler uses \(a(n)\) _______ to locate the classes it needs in the classpath. t) The classpath for the compiler and \(J V M\) can be specified with the ______ option to the javac or java command, or by setting the ______ environment variable. u) Set methods are commonly called _______ because they typically change a value. v) \(A(n)\) _______ imports all static members of a class. w) The public methods of a class are also known as the class's _______ or _______.

Create a class called Rational for performing arithmetic with fractions. Write a program to test your class. Use integer variables to represent the private instance variables of the class - the numerator and the denominator. Provide a constructor that enables an object of this class to be initialized when it's declared. The constructor should store the fraction in reduced form. The fraction \(2 / 4\) is equivalent to \(1 / 2\) and would be stored in the object as 1 in the numerator and 2 in the denominator. Provide a no-argument constructor with default values in case no initializers are provided. Provide public methods that perform each of the following operations: a) Add two Rational numbers: The result of the addition should be stored in reduced form. Implement this as a static method. b) Subtract two Rational numbers: The result of the subtraction should be stored in reduced form. Implement this as a static method. c) Multiply two Rational numbers: The result of the multiplication should be stored in reduced form. Implement this as a static method. d) Divide two Rational numbers: The result of the division should be stored in reduced form. Implement this as a static method. e) Return a String representation of a Rational number in the form a/b, where a is the numerator and b is the denominator. Peturn a String representation of a Rational number in floating-point format. (Consider providing formatting capabilities that enable the user of the class to specify the number of digits of precision to the right of the decimal point.)

Create a class called Complex for performing arithmetic with complex numbers. Complex numbers have the form \\[ \text {reallart }+\text { imaginaryPart }^{*} \\] where \(i\) is \\[ \sqrt{-1} \\] Write a program to test your class. Use floating-point variables to represent the private data of the class. Provide a constructor that enables an object of this class to be initialized when it's declared. Provide a no-argument constructor with default values in case no initializers are provided. Provide public methods that perform the following operations: a) Add two Complex numbers: The real parts are added together and the imaginary parts are added together. b) Subtract two Complex numbers: The real part of the right operand is subtracted from the real part of the left operand, and the imaginary part of the right operand is subtracted from the imaginary part of the left operand. c) Print Complex numbers in the form (realPart, imageinaryPart).

Create class SavingsAccount. Use a static variable annual InterestRate to store the annual interest rate for all account holders. Each object of the class contains a private instance variable savingsBalance indicating the amount the saver currently has on deposit. Provide method calculateMonth 7 yInterest to calculate the monthly interest by multiplying the savingsBalance by annualInterestRate divided by \(12-\) this interest should be added to savingsBalance. Provide a static method modifyInterestRate that sets the annual InterestRate to a new value. Write a program to test class SavingsAccount. Instantiate two savingsAccount objects, saver1 and saver \(2,\) with balances of \(\$ 2000.00\) and \(\$ 3000.00,\) respectively. Set annual InterestRate to \(4 \%,\) then calculate the monthly interest for each of 12 months and print the new balances for both savers. Next, set the annual InterestRate to \(5 \%\), calculate the next month's interest and print the new balances for both savers.
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