OOPJ Unit 04 - Inheritance & Abstraction

Questions and Answers

What will be the output when the main method is executed in the DemoMultilevel class?

Method of class A Method of class B Method of class C

Method of class B

Method of class A Method of class B Method of class C Method of class A

Method of class A (correct)

In the provided example, what type of inheritance is illustrated?

Single Inheritance

Hierarchical Inheritance

Multilevel Inheritance (correct)

Multiple Inheritance

Which method is not defined in the provided code?

displayA()

displayD() (correct)

displayC()

displayB()

Which class directly extends class A in the code example?

Class B Signup and view all the answers

What is the visibility of the methods defined in the classes A, B, and C?

Public Signup and view all the answers

What is one primary purpose of a copy constructor in the context provided?

To create a new object as a copy of an existing object Signup and view all the answers

What happens when a copy constructor is invoked in the code provided?

A new object is created with the same attributes as the original Signup and view all the answers

Which of the following statements is true about constructor overloading?

Multiple constructors can exist within a single class with different signatures Signup and view all the answers

In the example provided, what is the output when the default constructor is invoked?

Constructor 1 Signup and view all the answers

What is the significance of invoking the display method in the DemoCopy class?

It shows the values of name and rollno for the Student object Signup and view all the answers

Why does constructor overloading not require a return type?

Because constructors are not methods Signup and view all the answers

What output is expected when the line `Student s2 = new Student(s1);` is executed?

Copy Constructor is Invoked Signup and view all the answers

What parameters are used by the Balance class constructors in the given example?

One constructor with a double parameter and another with no parameters Signup and view all the answers

What is a key characteristic of method overriding?

It must match the argument list of the overridden method. Signup and view all the answers

Which statement accurately describes method overloading?

The argument list must change when overloaded. Signup and view all the answers

What happens when a method in class B overrides a method in class A?

Both methods can be called independently. Signup and view all the answers

What is the return type requirement for overriding a method?

It must match the return type of the overridden method. Signup and view all the answers

In which scenario is method overloading applicable?

When methods share the same name but have different parameters. Signup and view all the answers

What is the primary difference between method overloading and method overriding?

Overloading is resolved at compile time and overriding at runtime. Signup and view all the answers

Which statement about private and final methods is correct in relation to overloading and overriding?

Final methods can be overloaded but not overridden. Signup and view all the answers

What type of binding is used in method overriding?

Dynamic binding Signup and view all the answers

What does a class need to declare if it does not perform all behaviors of the interface?

The class must declare itself as abstract. Signup and view all the answers

In the example provided, what does the method demo() print when executed?

Value of i is :: 10 Signup and view all the answers

What ability does an interface have with regards to other interfaces?

An interface can extend multiple interfaces. Signup and view all the answers

Which of the following correctly describes the relationship between interfaces and classes in Java?

A class must implement all methods defined in its interfaces. Signup and view all the answers

What is the output of the getdata() method from the InheritInterface class after setting the data?

getdata() will print 'Welcome To Heaven'. Signup and view all the answers

What does the setdata() method in the InheritInterface class do?

It takes a parameter to assign to the display variable. Signup and view all the answers

How would you describe the characteristic of interfaces in Java?

Interfaces only define methods and cannot have constructors. Signup and view all the answers

What happens if a class does not implement all the methods in the interface it uses?

The class must be marked as abstract. Signup and view all the answers

What is required to implement multiple inheritance in Java using interfaces?

A class must implement all methods from the interfaces Signup and view all the answers

Which statement accurately describes an interface in Java?

All methods in an interface are abstract by default Signup and view all the answers

Which of the following statements is true regarding class and interface in Java?

A class can be instantiated, but an interface cannot be instantiated Signup and view all the answers

What will the method 'getdata()' do in the class that implements interfaces A and B?

Print 'Welcome to Heaven' Signup and view all the answers

What type of variables can be found in an interface?

Static final variables only Signup and view all the answers

How do you create an object of a class that implements multiple interfaces in Java?

Using new Keyword Signup and view all the answers

What is the correct method signature for a method in interface A?

public void setdata(String name) Signup and view all the answers

Which of the following is an example of multiple inheritance in Java?

A class implementing multiple interfaces Signup and view all the answers

Study Notes

Copy Constructor

A copy constructor creates a new object as a copy of an existing object.
Syntax example: Student(Student s) { ... }
Inside the constructor, member variables are assigned values from the copied object.

Constructor Overloading

Allows multiple constructors in a single class without return types.
Example:
- Default constructor: Balance() { ... }
- Parameterized constructor: Balance(double b) { ... }

Multilevel Inheritance

Involves multiple classes in a hierarchy where a class derives from another derived class.
Example demonstrates classes A, B, and C with methods to display hierarchy:
- class C extends B { ... }
- Calling methods from parent classes.

Method Overriding

Allows a subclass to provide a specific implementation of a method that is already defined in its superclass.
Example shows method display() in classes A and B where B overrides A's implementation.

Method Overloading vs. Method Overriding

Method Overloading:
- Methods share the same name but differ in parameter lists.
- Can have different return types.
- Works within the same class, demonstrating compile-time polymorphism.
Method Overriding:
- Must match the method signature of the superclass.
- Demonstrates run-time polymorphism with dynamic binding.

Interfaces

Interfaces define contracts that classes must adhere to, implementing specified methods.
An abstract class must be declared if it doesn’t implement all interface methods.

Inheritance of Interfaces

An interface can extend another interface, allowing a class to implement multiple interfaces.
Example illustrates interface inheritance between interfaces A and B.

Multiple Inheritance Using Interfaces

A class can implement multiple interfaces, allowing for multiple inheritance.
Each interface can have distinct method definitions, which the implementing class must provide.

Classes vs. Interfaces

Class:
- Can be instantiated, contains constructors.
- Methods can be concrete or abstract.
Interface:
- Cannot be instantiated, does not have constructors.
- All methods are abstract by default; variables are static final.

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Test your knowledge on key concepts from Unit 04 of the OOPJ course, focusing on inheritance and abstraction. This quiz covers important topics such as copy constructors and object-oriented programming principles in Java. Ideal for students who are preparing for exams in this subject.