1Z0-819 Java Fundamentals & Object-Oriented Programming 5

Question 1

Which of the following is an example of a widening primitive conversion?

Accepted Answer

int to long

Answer

Converting int to long is widening because long can represent all values an int can hold without data loss.

Question 2

What is the output of: `System.out.println("5" + 2 + 3);`?

Accepted Answer

523

Answer

String concatenation is left-associative: `"5" + 2` yields `"52"`, then `"52" + 3` yields `"523"`.

Question 3

Which OOP principle does encapsulation primarily support?

Accepted Answer

Hiding internal implementation details behind a public interface

Answer

Encapsulation bundles data and methods together and restricts direct access to internal state, exposing only a controlled public API.

Question 4

In Java, what is a 'has-a' relationship implemented through?

Accepted Answer

Composition (field reference)

Answer

A 'has-a' relationship is modeled by composition: one class holds a reference to another class as a field.

Question 5

What happens when you try to instantiate an abstract class directly with `new AbstractClass()`?

Accepted Answer

A compilation error occurs

Answer

The Java compiler rejects any attempt to instantiate an abstract class, producing a compilation error.

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