1Z0-811 Object-Oriented Programming Practice Question
A developer writes a class 'Vehicle' with a method 'move()' that prints 'Vehicle moves'. A subclass 'Car' overrides 'move()' to print 'Car moves'. Given: Vehicle v = new Car(); v.move(); What is the output?
⚠ Common exam trap
The trap here is that candidates mistakenly apply static binding (thinking the compiler uses the reference type 'Vehicle' to call 'move()'), ignoring Java's runtime polymorphism for overridden instance methods.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Car moves
Java uses dynamic method dispatch (runtime polymorphism). Even though the reference variable is of type 'Vehicle', the actual object is a 'Car' instance. At runtime, the JVM calls the overridden 'move()' method of the 'Car' class, printing 'Car moves'.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Vehicle moves
Why it's wrong here
Static binding would give this, but method overriding uses dynamic binding.
- ✗
Runtime exception
Why it's wrong here
No exception; method invocation is valid.
- ✗
Compilation fails
Why it's wrong here
The code compiles fine; Car is a subclass of Vehicle.
- ✓
Car moves
Why this is correct
Correct due to polymorphism; the overridden method in Car is called.
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