1Z0-819 Java Fundamentals & Object-Oriented Programming 4

Question 1

Which of the following correctly describes polymorphism in Java?

Accepted Answer

A reference type can behave differently depending on the actual object it points to at runtime

Answer

Polymorphism allows a supertype reference to invoke overridden methods on subtype objects, with the actual behavior determined at runtime.

Question 2

What is the default value of an instance variable of type `boolean` in Java?

Accepted Answer

false

Answer

Instance variables of type boolean are initialized to false by default when a class is instantiated.

Question 3

Given `List list = new ArrayList<>(); list.add("x");`, which statement causes a compilation error?

Accepted Answer

list.add(1)

Answer

`list.add(1)` attempts to add an Integer to a List<String>, violating the generic type constraint and causing a compilation error.

Question 4

Which statement about constructors in Java is correct?

Accepted Answer

Constructors can be overloaded

Answer

Multiple constructors with different parameter lists (overloading) are allowed and commonly used to provide flexible object initialization.

Question 5

What does the `instanceof` operator return when the left operand's type is a subtype of the right operand?

Accepted Answer

true

Answer

`instanceof` returns true whenever the object on the left is an instance of the class or any of its subtypes on the right.

(1Z0-819) Oracle Java SE 11 Developer Practice Test