Advance Java Quiz

What is the purpose of access modifiers in Java?

• To handle exceptions

• To create new data types

• To increase the performance of the code

• To define the visibility of classes and members

Answer explanation

Access modifiers in Java, such as public, private, and protected, define the visibility of classes and their members. This controls how other classes can interact with them, ensuring encapsulation and security.

What does a class declaration with the 'final' keyword indicate?

• The class cannot be subclassed

• The class is public

• The class can be subclassed

• The class is abstract

Answer explanation

A class declared with the 'final' keyword cannot be subclassed, meaning no other class can extend it. This ensures that the class's behavior remains unchanged and is useful for preventing inheritance.

What is the main purpose of an abstract class?

• To be extended by other classes

• To contain only static methods

• To be instantiated directly

• To provide default implementations

Answer explanation

The main purpose of an abstract class is to be extended by other classes. It cannot be instantiated directly and may contain methods that subclasses must implement, making it a blueprint for derived classes.

Which of the following is true about default access in Java?

• It is the same as public access

• It has no modifier preceding the class declaration

• It restricts access to the same class only

• It allows access from any package

Answer explanation

In Java, default access occurs when no access modifier is specified before a class declaration. This means the class is accessible only within its own package, not the same class only, making the correct choice: 'It has no modifier preceding the class declaration'.

What is the purpose of enums in Java?

• To create classes with multiple instances

• To restrict a variable to predefined values

• To handle exceptions

• To define new data types

Answer explanation

Enums in Java are used to restrict a variable to predefined values, ensuring that it can only take on specific, fixed values defined in the enum. This enhances type safety and code readability.

How do you declare an array in Java?

• By stating the type followed by square brackets

• By using the 'array' keyword

• By defining a new class

• By importing the array library

Answer explanation

In Java, you declare an array by stating the type followed by square brackets (e.g., int[] myArray). This syntax indicates the data type of the elements and the array structure, making it the correct choice.

What does it mean for class A to access class B?

• Class A can only access static members of class B

• Class A can modify class B directly

• Class A can only see public methods of class B

• Class A can create an instance of class B

Answer explanation

For class A to access class B means class A can create an instance of class B. This allows class A to utilize the methods and properties of class B, which is essential for object-oriented programming.

Which keyword is used to prevent a class from being subclassed?

• private

• final

• static

• abstract

Answer explanation

The keyword 'final' is used in Java to prevent a class from being subclassed. When a class is declared as final, it cannot be extended, ensuring its implementation remains unchanged.

What is the result of trying to instantiate an abstract class?

• It will result in a compiler error

• It will compile successfully

• It will create an instance of the subclass

• It will result in a runtime error

Answer explanation

Instantiating an abstract class is not allowed in object-oriented programming. It will result in a compiler error because abstract classes are meant to be subclassed, not directly instantiated.

What is the correct way to declare a public class in Java?

• ClassName class public {}

• public class ClassName {}

• class ClassName public {}

• public ClassName class {}

Answer explanation

The correct way to declare a public class in Java is 'public class ClassName {}'. This syntax specifies the access modifier 'public' before the 'class' keyword, followed by the class name.