Understanding OOP Concepts in Java

What is method overriding in Java?

• Method overriding allows a subclass to inherit all methods from its superclass without changes.

• Method overriding is when a superclass provides a new implementation of a method.

• Method overriding is a way to create multiple methods with the same name in the same class.

• Method overriding allows a subclass to provide a specific implementation of a method that is already defined in its superclass.

How does method overloading differ from method overriding?

• Method overloading changes the return type only; method overriding changes the method name.

• Method overloading is about multiple methods in the same class with different signatures; method overriding is about redefining a superclass method in a subclass.

• Method overloading requires inheritance; method overriding does not.

• Method overloading is used for private methods; method overriding is for public methods.

What is an abstract class in Java?

• An abstract class can be instantiated directly.

• An abstract class cannot contain any methods.

• An abstract class is a class that has no fields.

• An abstract class in Java is a class that cannot be instantiated and may contain abstract methods that must be implemented by subclasses.

Can you instantiate an abstract class? Why or why not?

• Abstract classes can be instantiated if they have implemented methods.

• No, you cannot instantiate an abstract class.

• Yes, you can instantiate an abstract class.

• You can instantiate an abstract class with a concrete subclass.

What is the purpose of an interface in Java?

• To create a new data type that cannot be instantiated.

• To provide a default implementation for methods in a class.

• To store data in a structured format.

• The purpose of an interface in Java is to define a contract for classes to implement, allowing for abstraction and multiple inheritance.

How do you implement an interface in a class?

• class MyClass uses MyInterface { /* method implementations */ }

• class MyClass implements MyInterface { /* method implementations */ }

• class MyClass implements MyClass { /* method implementations */ }

• class MyClass extends MyInterface { /* method implementations */ }

What is polymorphism in the context of OOP?

• Polymorphism is the technique of hiding the implementation details of a class.

• Polymorphism is the process of combining multiple classes into one.

• Polymorphism is the ability of different classes to be treated as instances of the same class through a common interface.

• Polymorphism refers to the ability of a class to inherit properties from multiple parent classes.

Provide an example of polymorphism using method overriding.

• class Animal { void sound() { System.out.println("Animal runs"); } }

• class Animal { void sound() { System.out.println("Animal makes a sound"); } } class Dog extends Animal { void sound() { System.out.println("Dog barks"); } } class Cat extends Animal { void sound() { System.out.println("Cat meows"); } } Animal myDog = new Dog(); Animal myCat = new Cat(); myDog.sound(); // Outputs: Dog barks myCat.sound(); // Outputs: Cat meows

• class Dog extends Animal { void sound() { System.out.println("Dog sleeps"); } }

• Animal myDog = new Animal(); myDog.sound(); // Outputs: Animal makes a sound

What is encapsulation and how does it relate to abstraction?

• Encapsulation allows direct access to an object's internal state without restrictions.

• Encapsulation is the process of creating multiple classes in a program.

• Abstraction is the same as encapsulation and does not serve a different purpose.

• Encapsulation is the bundling of data and methods that operate on that data, while abstraction is the concept of hiding complex implementation details. Encapsulation supports abstraction by restricting access to the internal state of an object.

Explain the concept of upcasting in Java.

• Upcasting is the conversion of a superclass reference to a subclass reference in Java.

• Upcasting is a method to create new instances of a class in Java.

• Upcasting is the conversion of a subclass reference to a superclass reference in Java.

• Upcasting refers to the process of casting primitive types to object types in Java.