Visibility Modifiers and Accessors in Java
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Visibility Modifiers and Accessors in Java

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Questions and Answers

What can be said about members of a class declared with private visibility?

  • They can be accessed from any class within the same package.
  • They are accessible to subclasses regardless of package.
  • They can only be accessed within the declaring class. (correct)
  • They can be referenced anywhere in the application.

    • Why should instance variables generally not be declared with public visibility?

  • It complicates the code and makes it harder to read.
  • It prevents the use of accessors and mutators.
  • It allows clients to directly modify the values, violating encapsulation. (correct)
  • Public variables are not supported in modern programming practices.

    • What is the primary role of public methods in a class?

  • To manage the internal state of the class.
  • To provide services to clients. (correct)
  • To initialize instance variables.
  • To serve as temporary data storage.

    • Which of the following best describes the relationship between service methods and support methods?

    <p>Support methods assist service methods and are not intended for client access.</p> Signup and view all the answers

    What is the naming convention for accessor methods in a class?

    <p>getX or setX</p> Signup and view all the answers

    Which type of variable is permissible to have public visibility without violating encapsulation?

    <p>Constant</p> Signup and view all the answers

    In what situation would a class typically use accessor and mutator methods?

    <p>When the class encapsulates its instance data.</p> Signup and view all the answers

    Which statement accurately represents the default visibility of class members?

    <p>They can only be accessed by classes in the same package.</p> Signup and view all the answers

    What is the purpose of a mutator in a class?

    <p>To restrict how a client's options to modify an object's state.</p> Signup and view all the answers

    Why would MAX be declared as public in the Die class?

    <p>Since MAX is a constant, its value cannot be changed, preserving encapsulation.</p> Signup and view all the answers

    How does flow control work when a method is invoked?

    <p>The flow jumps to the invoked method and executes its code.</p> Signup and view all the answers

    What happens after a method completes its execution?

    <p>Control flow continues from the point of method invocation.</p> Signup and view all the answers

    What is the significance of declaring the faceValue variable as private in the Die class?

    <p>It allows restricted access, ensuring modifications are made through its mutator methods.</p> Signup and view all the answers

    What does a method declaration specify?

    <p>The code that will be executed upon invoking the method.</p> Signup and view all the answers

    What does it indicate when a method is called from another class?

    <p>The method must be declared as public.</p> Signup and view all the answers

    What is the key restriction on values set by a mutator?

    <p>Values must fall within specially determined limits.</p> Signup and view all the answers

    What does the integer faceValue in the Die class represent?

    <p>The current state of the Die object</p> Signup and view all the answers

    What is the interest rate for the bank account represented in the code?

    <p>3.5%</p> Signup and view all the answers

    Which statement accurately describes the roll method in the Die class?

    <p>It randomly generates a value for faceValue between 1 and 6.</p> Signup and view all the answers

    In the RollingDice class, what does the expression die2.setFaceValue(4) do?

    <p>It sets the current value of die2 to 4 without rolling.</p> Signup and view all the answers

    Which method is called to add interest to the account?

    <p>addInterest()</p> Signup and view all the answers

    What is the result of the expression sum = die1.getFaceValue() + die2.getFaceValue()?

    <p>It retrieves and adds the current face values of die1 and die2.</p> Signup and view all the answers

    What value is the output of 'acct2.withdraw(430.75, 1.50)' based on the provided output?

    <p>107.55</p> Signup and view all the answers

    What is the purpose of the constructor in the Account class?

    <p>To initialize account attributes</p> Signup and view all the answers

    Why is it advantageous for the Die class to be designed as a versatile and reusable resource?

    <p>It allows for multiple instances of dice that behave consistently.</p> Signup and view all the answers

    What would happen if the roll method in the Die class is called repeatedly?

    <p>FaceValue will be set to a different random number each time.</p> Signup and view all the answers

    Which class likely represents multiple accounts in the output provided?

    <p>Account</p> Signup and view all the answers

    How does the RollingDice class utilize the Die class?

    <p>It creates and rolls instances of the Die class to simulate dice rolls.</p> Signup and view all the answers

    Which balance represents the account of Ted Murphy?

    <p>$132.90</p> Signup and view all the answers

    What will the output be if both dice are rolled and displayed as die1 and die2?

    <p>'Die One: random_value, Die Two: random_value' for each roll.</p> Signup and view all the answers

    What operation did the print statement 'System.out.println(acct2)' perform?

    <p>Prints the account details</p> Signup and view all the answers

    What will happen if a negative amount is passed to the withdraw method?

    <p>It will throw an error.</p> Signup and view all the answers

    What is indicated by the return type of a method?

    <p>The type of value the method sends back</p> Signup and view all the answers

    What do we call the variables listed in a method's header?

    <p>Formal parameters</p> Signup and view all the answers

    In the method declaration public char calc(int num1, int num2, String message), what is char?

    <p>The return type</p> Signup and view all the answers

    What is the purpose of the return statement in a method?

    <p>To specify the value to be returned</p> Signup and view all the answers

    In the invocation ch = obj.calc(25, count, 'Hello');, what are 25, count, and 'Hello' classified as?

    <p>Actual parameters</p> Signup and view all the answers

    What happens to local variables such as sum and result after the method execution is completed?

    <p>They are destroyed after the method finishes executing</p> Signup and view all the answers

    What must the expression in a return statement be consistent with?

    <p>The return type</p> Signup and view all the answers

    Which of the following best describes a method with a void return type?

    <p>It does not return any value</p> Signup and view all the answers

    Study Notes

    Visibility Modifiers

    • Public visibility allows referencing members anywhere.
    • Private visibility restricts referencing members to within the class.
    • Members without a visibility modifier have default visibility, allowing referencing by classes in the same package.
    • Public variables violate encapsulation because they allow direct manipulation of values by clients.
    • Instance variables should not be declared with public visibility.
    • Public constants do not violate encapsulation, as clients cannot modify their values.
    • Public methods, also known as service methods, provide object services to clients.
    • Support methods are internal, not intended for client calls, thus declared with non-public visibility.

    Accessors and Mutators

    • Accessor methods retrieve the current value of a variable.
    • Mutator methods modify the value of a variable.
    • Accessor method names usually follow the pattern getX, where X is the variable name.
    • Mutator method names usually follow the setX pattern.
    • These methods are often called "getters" and "setters".

    Mutator Restrictions

    • Mutators allow controlling how clients modify an object's state.
    • They can enforce limits on variable values, preventing invalid assignments.

    Methods

    • A method declaration specifies the code executed when the method is invoked (called).
    • When invoked, control jumps to the method, executes its code, and returns to the calling location.
    • Methods can return a value or not, depending on the definition.
    • If the called method is in the same class, only the method name is required for invocation.
    • If the method is in another class or object, the object name and method are used for invocation.

    Method Header

    • A method declaration starts with a method header.
    • It includes the method's modifier, return type, name, and parameter list.
    • The parameter list specifies the type and name of each parameter.
    • Parameter names in the method declaration are known as formal parameters.

    Method Body

    • The method body follows the header.
    • It contains the code to be executed when the method is invoked.
    • Local data declared within the method body are created when the method is called and destroyed when it finishes.

    The return Statement

    • The return type of a method indicates the type of value it returns to the caller.
    • Methods that do not return a value have a void return type.
    • The return statement specifies the value to be returned.
    • The return expression must match the method's return type.

    Parameters

    • When a method is called, the provided actual parameters in the invocation are copied to the formal parameters in the method header.
    • Each parameter in the invocation is matched with its corresponding formal parameter in the method header.

    Classes

    • The values of an object's data define its state.
    • An object's methods define its behaviors.
    • Any specific program may not use all operations provided by a class.

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    Description

    This quiz covers the concepts of visibility modifiers and their impact on encapsulation in Java. You will also learn about accessor and mutator methods, including their naming conventions. Test your understanding of these fundamental principles in object-oriented programming.

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