Java Abstract Classes

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What is true about abstract classes in Java?

They cannot contain abstract methods.

They can be instantiated using the new operator.

They can be used as a data type. (correct)

They cannot have constructors.

What is the main difference between an abstract class and a concrete class?

An abstract class can be instantiated, while a concrete class cannot.

An abstract class is used for multiple inheritance, while a concrete class is used for single inheritance.

A concrete class can be instantiated, while an abstract class cannot. (correct)

A concrete class is used for multiple inheritance, while an abstract class is used for single inheritance.

Can a subclass be abstract if its superclass is concrete?

It depends on the type of superclass.

It depends on the type of inheritance.

Yes, it can be abstract. (correct)

No, it must be concrete.

What is an interface primarily used for in Java?

Defining common behavior for classes, including unrelated classes Signup and view all the answers

What is the purpose of constructors in an abstract class?

To be used by subclasses. Signup and view all the answers

Can an abstract class contain abstract methods?

Yes, it can. Signup and view all the answers

What is the relationship between an abstract class and its subclass?

The subclass can be abstract or concrete. Signup and view all the answers

What is a characteristic of an interface in Java?

It can be used as a data type Signup and view all the answers

What is the primary reason for declaring an abstract method in a class?

To declare a method that must be implemented by subclasses. Signup and view all the answers

What happens when a class implements an interface?

The class must provide implementations for all the methods declared in the interface Signup and view all the answers

What can an abstract class contain?

Either abstract methods, concrete methods, or both. Signup and view all the answers

What is the difference between an interface and an abstract class?

An abstract class can have implementation, while an interface cannot Signup and view all the answers

Can an abstract class be instantiated?

No, but it can be subclassed. Signup and view all the answers

What happens if a subclass of an abstract superclass does not implement all the abstract methods?

The subclass is automatically abstract. Signup and view all the answers

What is the difference between an abstract class and a concrete class?

An abstract class cannot be instantiated, while a concrete class can. Signup and view all the answers

What is the purpose of an abstract class?

To provide a blueprint for subclasses. Signup and view all the answers

What is the purpose of defining an interface in Java?

To specify common behavior for objects Signup and view all the answers

What is a key advantage of using interfaces in Java?

It allows for multiple inheritance of behavior Signup and view all the answers

Java Abstract Classes

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