SCJP Basic 5 — Questions and Answers
Question 1: Which of the following correctly describes an abstract class in Java?
- It cannot have any methods
- It can be instantiated directly
- It may contain abstract and concrete methods (Correct answer)
- It must implement all interface methods
Correct answer: It may contain abstract and concrete methods
An abstract class can have a mix of abstract (no body) and concrete (with body) methods.
Question 2: What is the result of comparing two String objects with == in Java?
- Always true if contents are equal
- Compares object references, not content (Correct answer)
- Causes a compile error
- Throws NullPointerException
Correct answer: Compares object references, not content
== on objects checks reference equality (same memory address), not the content of the strings.
Question 3: Which of the following is true about a Java interface before Java 8?
- It can have instance variables
- It can have constructors
- All methods are implicitly public and abstract (Correct answer)
- It can extend multiple abstract classes
Correct answer: All methods are implicitly public and abstract
Prior to Java 8, interface methods were implicitly public and abstract and could not have implementations.
Question 4: What is the scope of a variable declared inside a for-loop initializer?
- The entire class
- The entire method
- Only within the for-loop block (Correct answer)
- The entire package
Correct answer: Only within the for-loop block
A variable declared in a for-loop initializer is scoped to the for-loop block only.
Question 5: Which of the following statements about Java arrays is true?
- Arrays can grow dynamically
- Arrays in Java are objects stored on the heap (Correct answer)
- Array indices start at 1
- Arrays can hold multiple types simultaneously
Correct answer: Arrays in Java are objects stored on the heap
Java arrays are objects allocated on the heap with a fixed size determined at creation.
Question 6: What is the output of the following code? int x = 5; System.out.println(x++);
- 6
- 5 (Correct answer)
- Compile error
- 4
Correct answer: 5
The post-increment operator returns the original value (5) before incrementing x to 6.
Question 7: Which of the following correctly describes encapsulation in Java?
- Inheriting methods from a parent class
- Hiding internal state and requiring access through public methods (Correct answer)
- Using multiple classes to define one object
- Preventing a class from being instantiated
Correct answer: Hiding internal state and requiring access through public methods
Encapsulation bundles data (fields) with methods that operate on it and restricts direct access using access modifiers.
SCJP Basic 5
Which of the following correctly describes an abstract class in Java?