OCP Java Class Design and OOP 2

Question 1

Which keyword prevents a method from being overridden in a subclass?

Accepted Answer

final

Answer

static

Answer

private

Answer

abstract

Question 2

What happens when a class is declared `abstract` and contains no abstract methods?

Accepted Answer

The class cannot be instantiated but can be subclassed

Answer

Compilation error

Answer

It behaves exactly like a concrete class

Answer

Only static methods are allowed

Question 3

Given: `class A { int x = 5; }` and `class B extends A { int x = 10; }`, what does `((A) new B()).x` evaluate to?

Accepted Answer

5

Answer

10

Answer

Compilation error

Answer

Runtime exception

Question 4

Which of the following correctly describes a covariant return type in Java?

Accepted Answer

An overriding method can return a subtype of the original return type

Answer

An overriding method can return a supertype of the original return type

Answer

An overriding method must return the same type as the original

Answer

Covariant return types are not supported in Java

Question 5

What is the result of calling a `default` interface method when a class implements two interfaces that define the same default method?

Accepted Answer

Compilation error unless the class overrides the method

Answer

The first interface's method is used

Answer

The JVM picks one at runtime

Answer

Both methods are called in sequence

Question 6

Which access modifier makes a member visible only within the same package and to subclasses in other packages?

Accepted Answer

protected

Answer

private

Answer

public

Answer

package-private (no modifier)

Question 7

What is the effect of marking a constructor `private` in a class?

Accepted Answer

The class cannot have any subclasses and cannot be instantiated outside the class

Answer

Only the class cannot be subclassed

Answer

Only instances cannot be created from outside the class

Answer

The class is treated as abstract