Unit 2 - Classes and Objects
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What is the primary purpose of the setdim method in the Box class?

  • To initialize the dimensions of the box. (correct)
  • To create a new `Box` object.
  • To calculate the volume of the box.
  • To print the dimensions of the box.

    • Which of the following statements accurately describes the concept of encapsulation?

  • The ability of a class to inherit properties and methods from another class.
  • The process of creating abstract classes that define general behaviors.
  • The process of hiding data and methods within a class, exposing only necessary functionalities. (correct)
  • The ability of an object to take on different forms based on the context.

    • What is the role of the main method in the p16_classdemo1 class?

  • To define the dimensions of the `Box` object.
  • To create a new `Box` object and calculate its volume. (correct)
  • To display the volume of the calculated `Box` object.
  • To provide input to the `Box` object's methods.

    • Why are the variables w, h, and d declared as private in the Box class?

    <p>To enforce data hiding and protect them from direct access. (C)</p> Signup and view all the answers

    How is the volume method called in the p16_classdemo1 class?

    <p><code>b1.volume()</code> (D)</p> Signup and view all the answers

    What would be the output of the code if the line b1.setdim(10, 20, 15); in the p16_classdemo1 class is removed?

    <p>The program will compile with errors, because the <code>volume</code> method cannot be called without initialized dimensions. (A)</p> Signup and view all the answers

    In the given example, which of these classes are used for implementing encapsulation?

    <p>The <code>Box</code> class only. (C)</p> Signup and view all the answers

    What is the purpose of the 'this' keyword in Java?

    <p>To refer to the current object within a method or constructor. (B)</p> Signup and view all the answers

    In which scenarios can the 'this' keyword be used?

    <p>Within both constructors and instance methods. (D)</p> Signup and view all the answers

    How does the 'this' keyword help with variable hiding?

    <p>It allows accessing instance variables when a local variable has the same name. (B)</p> Signup and view all the answers

    What is the purpose of the 'this' keyword in the following code snippet: this.w = w;?

    <p>To initialize the instance variable <code>w</code> with the value of the local variable <code>w</code>. (C)</p> Signup and view all the answers

    How can the 'this' keyword be used within a method?

    <p>To call another method of the same class. (B)</p> Signup and view all the answers

    What is the purpose of using the 'this' keyword to call methodOne() in the following code snippet: this.methodOne();?

    <p>To call the <code>methodOne()</code> method of the same class. (C)</p> Signup and view all the answers

    In what context is the 'this' keyword used to call another constructor?

    <p>To call a constructor from the same class that has different parameters. (A)</p> Signup and view all the answers

    What happens when a local variable and an instance variable have the same name?

    <p>The local variable overrides the instance variable. (A)</p> Signup and view all the answers

    When is the 'this' keyword considered mandatory?

    <p>When initializing instance variables within a constructor. (C)</p> Signup and view all the answers

    What is the purpose of method overloading in Java?

    <p>To define methods with the same name but different parameter lists. (A)</p> Signup and view all the answers

    In the provided code example, what is the order in which constructors are called when a Testing object is created?

    <p>Design(), Coding(), Testing() (C)</p> Signup and view all the answers

    Which of the following is NOT a valid reason for using method overloading?

    <p>To define methods with different return types but the same name. (D)</p> Signup and view all the answers

    In the code example for multilevel inheritance, what is the relationship between the Coding class and the Testing class?

    <p>The <code>Coding</code> class is a superclass of the <code>Testing</code> class. (A)</p> Signup and view all the answers

    How does Java determine which version of an overloaded method to call when a method is invoked?

    <p>By the type and number of arguments passed to the method. (D)</p> Signup and view all the answers

    If class C does not have its own constructor, what will be the output when creating a new instance of C?

    <p>Constructor of A Constructor of B (D)</p> Signup and view all the answers

    Which of the following access modifiers is used when no explicit modifier is specified for a class, method, or data member?

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

    What is the primary purpose of access modifiers in Java?

    <p>Enforcing data hiding by restricting access to members of a class. (D)</p> Signup and view all the answers

    Why would you use the protected access modifier instead of public?

    <p>To allow access within the same package and from subclasses, even in different packages. (A)</p> Signup and view all the answers

    Given the code class B extends A { ... }, what can you infer about the relationship between classes A and B?

    <p>Class <code>B</code> inherits properties and methods from <code>A</code>. (B)</p> Signup and view all the answers

    Which of the following is NOT a Java access modifier?

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

    If you define a method as private, what is the implication of this choice?

    <p>The method can only be accessed within the same class where it is defined. (A)</p> Signup and view all the answers

    What is the purpose of the main method in Java?

    <p>To serve as the entry point for executing a Java program. (B)</p> Signup and view all the answers

    What is the difference between a class and an object in Java?

    <p>A class defines the structure and behavior of an object, and an object represents a specific instance of that structure and behavior. (A)</p> Signup and view all the answers

    In the given code snippet, what is the purpose of the new C() expression?

    <p>To create a new object of type <code>C</code> and assign it to the variable <code>ob</code>. (B)</p> Signup and view all the answers

    Which of the following is NOT a synonym for 'superclass'?

    <p>Derived class (A)</p> Signup and view all the answers

    In the provided code, what is the relationship between the 'outer' and 'inner' classes?

    <p>The 'inner' class is a non-static nested class (inner class) within the 'outer' class. (D)</p> Signup and view all the answers

    Can a subclass access private members of its superclass directly?

    <p>No, subclasses can only access public and protected members of their superclass. (B)</p> Signup and view all the answers

    In the provided code, why does 'inner' class's 'test1()' method print the value of 'x'?

    <p>The 'inner' class can directly access members of its enclosing class, including 'outer' class's 'x'. (A)</p> Signup and view all the answers

    What is the purpose of the 'test2()' method in the 'outer' class?

    <p>To demonstrate how an inner class can access members of its enclosing class. (B)</p> Signup and view all the answers

    Which of these is a correct statement regarding inner classes?

    <p>You can define an inner class even within a loop, for example, a for loop. (B)</p> Signup and view all the answers

    What is the difference between a static nested class and a non-static nested class (inner class) in Java?

    <p>A static nested class is associated with the outer class, while an inner class is associated with the object of the outer class. (B)</p> Signup and view all the answers

    What is the significance of the comment '// can’t access because y is of inner class.' in the code?

    <p>It explains that the 'outer' class cannot access the 'y' variable directly because it belongs to the 'inner' class, and 'inner' class's variables are scoped locally within the 'inner' class. (B)</p> Signup and view all the answers

    What is the primary advantage of using inheritance in object-oriented programming?

    <p>It allows multiple classes to share the same code and functionality, reducing redundancy. (A)</p> Signup and view all the answers

    Study Notes

    Unit 2 - Classes and Objects

    • Classes and objects are fundamental concepts in object-oriented programming (OOP).
    • A class defines a blueprint or template for creating objects.
    • An object is an instance of a class, embodying the data (attributes) and methods (actions) specified by the class.
    • Collectively, the methods and variables defined within a class are called members of the class.
    • Instance variables are the variables defined within a class. Each instance of the class contains its own copy of these variables.
    • The code contained within a class is called member methods; these embody the operations of an object.
    • Data hiding (or encapsulation) is one of the four fundamental OOP concepts (the other three are inheritance, polymorphism, and abstraction). Encapsulation is accomplished by declaring class variables as private and providing public getter and setter methods to access and modify the values.
    • A class, in Java, is a blueprint that defines a new data type.
    • An object, in Java, is an instance of a class. It is an actual implementation of the class's blueprint.
    • Java classes have several components such as: access controls (public, private, etc.), data or variables, methods, constructors, and inheritance.
    • Constructors are special methods automatically called at the moment an object of the declared class is created.
    • Constructors do not have explicit return types like void, etc.
    • There are two types of constructors, default constructor and parameterized constructor.
    • A default constructor is a constructor that does not take any arguments.
    • A parameterized constructor is a constructor that accepts one or more arguments.
    • Method overloading is a technique in Java where a class can have multiple methods with the same name but different parameter lists (number or type of parameters). The compiler differentiates between these methods based on the method parameters.
    • Method overriding is a feature in object-oriented programming where a subclass method overrides or redefines a method from its superclass. The method names and the method signatures (including parameters) must be identical to what exists in the superclass.
    • The this keyword can resolve name collisions between local variables and instance variables in a method or constructor. The keyword is useful when formal parameters in a method or constructor have the same name as instance variables within the same class.
    • The super keyword is used to refer to a parent class either to call a parent class method or to refer to a parent class variable. It should be used when calling a parent class method or variable in a subclass when there is a name clash between members in the parent and child class.
    • Static members (variables and methods in a class) are associated with the class rather than any object instances. A static member can be accessed by using only the class name. These members are useful for storing data accessed by all objects or when an operation is performed that does not depend on the specifics of a particular object.
    • A class can be declared as final; this means that that class cannot be subclassed. Similarly a method or variable in a class can also be declared as final—this prevents overriding of methods and prevents the modification of the value.
    • Polymorphism refers to a class' ability to have multiple forms. One way is through method overloading and a second is through method overriding. Method overloading is when methods have the same name but different signatures. Method overriding is when subclass methods redefine a method that exists in a superclass. The choice of method to be executed is resolved at run time based on the arguments used to call the method.
    • An interface defines a contract for a set of methods. It can only declare methods, without specific implementations. Methods in an interface are implicit abstract and public methods. Multiple interfaces can be implemented by a class, but only one class can be extended by another.
    • There are various ways to access class members depending on the access specifier (private, protected, default (package-private), and public) associated with the member. The scope or visibility of variables or methods depends on the access specifier that modifies them when they exist within a class.
    • The scope of a class member depends on the modifiers (access specifiers) that modify it. These can include private, protected, default (package private) and public.

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    Explore the fundamental concepts of object-oriented programming in this quiz. Learn about classes, objects, encapsulation, and the roles of instance variables and methods. Test your understanding of how these components work together to create effective OOP solutions.

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