Mastering Java OOP Concepts

What are the four main principles of Object-Oriented Programming?

• Inheritance, Overloading, Recursion, Serialization

• Composition, Aggregation, Delegation, Interface

• Encapsulation, Modularity, Scripting, Data Structures

• Encapsulation, Abstraction, Inheritance, Polymorphism

Define encapsulation and provide an example in Java.

• class Person { private String name; public String getName() { return null; } }

• class Person { private String name; public void displayName() { System.out.println(name); } }

• class Person { public String name; }

• Example in Java: class Person { private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } }

What is inheritance and how is it implemented in Java?

• Inheritance in Java allows a class to inherit fields and methods from another class using the 'extends' keyword.

• Inheritance allows a class to inherit only methods, not fields.

• Inheritance in Java is a way to create multiple classes from a single class without any relationship.

• Inheritance in Java is implemented using the 'implements' keyword.

Explain polymorphism and its types in Java.

• There are three types of polymorphism in Java: static, dynamic, and abstract.

• Polymorphism refers to the ability of a class to have multiple constructors.

• Polymorphism in Java has two types: Compile-time polymorphism (method overloading) and Runtime polymorphism (method overriding).

• Polymorphism in Java is only related to class inheritance.

What is an interface in Java and how does it differ from an abstract class?

• An interface is a type of class that cannot be instantiated, while an abstract class can be instantiated.

• An interface can only contain concrete methods, while an abstract class can have abstract methods only.

• An interface in Java is a contract that classes can implement, while an abstract class can provide some implementation and state.

• An interface can have instance variables, while an abstract class cannot.

Describe the concept of method overloading in Java.

• Method overloading is the ability to override methods in a subclass.

• Method overloading is the ability to define multiple methods in the same class with the same name but different parameter lists.

• Method overloading allows methods to have different names in the same class.

• Method overloading is when a method can only have one parameter.

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

• The 'super' keyword is used to access superclass methods and constructors.

• The 'super' keyword is used to define interfaces.

• The 'super' keyword is used to declare variables.

• The 'super' keyword is used to create new classes.

How does Java achieve abstraction?

• Through method overloading

• Java achieves abstraction using abstract classes and interfaces.

• By utilizing exception handling

• Using constructors and destructors

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

• A class is a blueprint for creating objects, while an object is an instance of a class.

• Classes and objects are the same in Java.

• An object is a blueprint for creating classes.

• A class is a type of object.

Explain the concept of constructors in Java and their types.

• Constructors are regular methods that return a value.

• Constructors are used to destroy objects in Java.

• Constructors can only be private and cannot be public.

• Constructors in Java are special methods for initializing objects, with types including default constructors and parameterized constructors.