Compile-Time vs Runtime Method Resolution | Oracle Certified Professional Java SE 17 Explained
This 1Z0-829 practice question tests your understanding of utilizing java object-oriented approach. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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
// File: com/example/Vehicle.java
public abstract class Vehicle {
public abstract void start();
}
// File: com/example/Car.java
public class Car extends Vehicle {
public void start() {
System.out.println("Car engine started");
}
public void drive() {
System.out.println("Car is moving");
}
}
// File: com/example/Test.java
public class Test {
public static void main(String[] args) {
Vehicle v = new Car();
v.start();
v.drive(); // Line 9
}
}
Refer to the exhibit. What is the result of compiling and running the Test class?
Exhibit
// File: com/example/Vehicle.java
public abstract class Vehicle {
public abstract void start();
}
// File: com/example/Car.java
public class Car extends Vehicle {
public void start() {
System.out.println("Car engine started");
}
public void drive() {
System.out.println("Car is moving");
}
}
// File: com/example/Test.java
public class Test {
public static void main(String[] args) {
Vehicle v = new Car();
v.start();
v.drive(); // Line 9
}
}
A
Runtime exception because drive() is not accessible.
Why wrong: Error is at compile time.
B
Prints "Car engine started" followed by "Car is moving".
Why wrong: Compilation error occurs before execution.
C
Compilation error because Car does not implement all abstract methods.
Why wrong: Car does implement start().
D
Compilation error at line 9 because Vehicle does not have a drive() method.
The reference type is Vehicle, which does not define drive().
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Compilation error at line 9 because Vehicle does not have a drive() method.
Option D is correct because the reference type of the variable `v` is `Vehicle`, and the `Vehicle` interface does not declare a `drive()` method. Since the compiler checks the reference type for method availability, calling `v.drive()` results in a compilation error, even though the actual object is a `Car` that has a `drive()` method.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Runtime exception because drive() is not accessible.
Why it's wrong here
Error is at compile time.
✗
Prints "Car engine started" followed by "Car is moving".
Why it's wrong here
Compilation error occurs before execution.
✗
Compilation error because Car does not implement all abstract methods.
Why it's wrong here
Car does implement start().
✓
Compilation error at line 9 because Vehicle does not have a drive() method.
Why this is correct
The reference type is Vehicle, which does not define drive().
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Oracle often tests the distinction between compile-time reference type checking and runtime polymorphism, trapping candidates who assume that the actual object's methods are always accessible through any reference variable.
Detailed technical explanation
How to think about this question
In Java, method resolution at compile time is based on the declared (reference) type, not the actual runtime type. This is a fundamental rule of polymorphism: the compiler only allows calls to methods that are visible in the reference type's class or interface. If the reference type lacks the method, a compilation error occurs, regardless of whether the actual object type has it. This prevents runtime surprises and enforces type safety.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Utilizing Java Object-Oriented Approach — This question tests Utilizing Java Object-Oriented Approach — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Compilation error at line 9 because Vehicle does not have a drive() method. — Option D is correct because the reference type of the variable `v` is `Vehicle`, and the `Vehicle` interface does not declare a `drive()` method. Since the compiler checks the reference type for method availability, calling `v.drive()` results in a compilation error, even though the actual object is a `Car` that has a `drive()` method.
What should I do if I get this 1Z0-829 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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