This 1Z0-829 practice question tests your understanding of utilizing java object-oriented approach. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: instance variable. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
Refer to the exhibit.
```
-- SQL to create table
CREATE TABLE departments (
dept_id INT PRIMARY KEY,
dept_name VARCHAR(50)
);
-- Materialized view with refresh
CREATE MATERIALIZED VIEW dept_summary
REFRESH COMPLETE ON DEMAND
AS
SELECT dept_id, COUNT(*) AS emp_count
FROM employees
GROUP BY dept_id;
-- Query
SELECT * FROM dept_summary;
```
What is a key difference between a class and an interface in Java?
Exhibit
Refer to the exhibit.
```
-- SQL to create table
CREATE TABLE departments (
dept_id INT PRIMARY KEY,
dept_name VARCHAR(50)
);
-- Materialized view with refresh
CREATE MATERIALIZED VIEW dept_summary
REFRESH COMPLETE ON DEMAND
AS
SELECT dept_id, COUNT(*) AS emp_count
FROM employees
GROUP BY dept_id;
-- Query
SELECT * FROM dept_summary;
```
A
A class cannot be used in inheritance.
Why wrong: Incorrect. Classes support inheritance; a class can extend another class or implement interfaces.
B
A class can contain instance variables, while an interface cannot.
Correct. A class can contain instance variables, while an interface cannot.
C
An interface is automatically updated when the implementing class changes.
Why wrong: Incorrect. Interfaces are not automatically updated; changes to implementing classes do not affect the interface definition.
D
An interface can be instantiated directly.
Why wrong: Incorrect. Interfaces cannot be instantiated directly; they must be implemented by a class.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A class can contain instance variables, while an interface cannot.
Option B is correct because classes can have instance variables (state), while interfaces cannot (they only declare method signatures and constants). This is a fundamental Java OOP concept.
Key principle: Instance variable
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
A class cannot be used in inheritance.
Why it's wrong here
Incorrect. Classes support inheritance; a class can extend another class or implement interfaces.
✓
A class can contain instance variables, while an interface cannot.
Why this is correct
Correct. A class can contain instance variables, while an interface cannot.
Related concept
Instance variable
✗
An interface is automatically updated when the implementing class changes.
Why it's wrong here
Incorrect. Interfaces are not automatically updated; changes to implementing classes do not affect the interface definition.
✗
An interface can be instantiated directly.
Why it's wrong here
Incorrect. Interfaces cannot be instantiated directly; they must be implemented by a class.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates might think that interfaces can have instance variables in Java 8+ with default methods, but interfaces still cannot have instance variables.
Detailed technical explanation
How to think about this question
Under the hood, a materialized view is essentially a table with a precomputed result set that can be indexed, partitioned, and analyzed like any physical table, which is why it is often used in data warehousing for star-schema aggregations. A subtle behavior is that when you query a materialized view, the optimizer may choose to use the materialized view even if the query references the base tables directly (query rewrite), but this requires the materialized view to be enabled for query rewrite and the session to have the appropriate initialization parameters. In real-world scenarios, materialized views are critical for dashboards that require sub-second response times on large datasets, as they avoid repeated expensive joins and aggregations.
KKey Concepts to Remember
Instance variable
Interface
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Instance variable
Real-world example
How this comes up in practice
A practitioner preparing for the 1Z0-829 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Instance variable Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Review instance variable, then practise related 1Z0-829 questions on the same topic to reinforce the concept.
The correct answer is: A class can contain instance variables, while an interface cannot. — Option B is correct because classes can have instance variables (state), while interfaces cannot (they only declare method signatures and constants). This is a fundamental Java OOP concept.
What should I do if I get this 1Z0-829 question wrong?
Review instance variable, then practise related 1Z0-829 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Instance variable
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