Java Fundamentals & Object-Oriented Programming Flashcards

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

Answer: int to long

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

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

Answer: 523

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

Which OOP principle does encapsulation primarily support?

Answer: Hiding internal implementation details behind a public interface

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

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

Answer: Composition (field reference)

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

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

Answer: A compilation error occurs

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

Which of the following best describes the difference between `==` and `.equals()` for String objects?

Answer: `==` compares references; `.equals()` compares content

`==` tests reference equality (same object in memory), while `String.equals()` tests value equality (same character sequence).

What is the purpose of a no-argument (no-arg) constructor?

Answer: It enables object creation without providing initial field values

A no-arg constructor allows a class to be instantiated without any arguments, which is also required by many frameworks for reflection-based object creation.