1Z0-811 Java Basics and Syntax Practice Question
A team is developing a library management system. They have a base class 'Item' with a method 'getTitle()' that returns the title. They also have a subclass 'Book' that overrides 'getTitle()'. In some places, they have a method that accepts an Item reference but actually receives a Book object. They want to call a method specific to Book, such as 'getISBN()', that is not in Item. They attempt to cast the parameter: ((Book) item).getISBN(). However, occasionally the program crashes with ClassCastException. What is the best practice to avoid this exception?
⚠ Common exam trap
Oracle often tests the misconception that catching `ClassCastException` is an acceptable way to handle invalid casts, when in fact the best practice is to use `instanceof` to prevent the exception entirely.
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
✓
Use if (item instanceof Book) before casting.
Using `instanceof` before casting ensures the object is actually an instance of `Book`, preventing a `ClassCastException` at runtime. This is the standard Java practice for safe downcasting when the object type is not guaranteed.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Use if (item instanceof Book) before casting.
Why this is correct
instanceof check prevents ClassCastException.
- ✗
Create a separate method for Book objects.
Why it's wrong here
Not practical for polymorphism.
- ✗
Catch ClassCastException and handle it.
Why it's wrong here
Exceptions should not be used for normal flow control.
- ✗
Change the parameter type to Object and then cast to Book.
Why it's wrong here
Does not solve the issue; still need to check instanceof.
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