Question 122 of 513
1Z0-829 Working with Arrays and Collections Practice Question
A developer writes the following code using Java 17: List<String> list = new ArrayList<>(); list.add("A"); list.add("B"); list.add(10); What is the result?
⚠ Common exam trap
The trap here is that candidates may mistakenly think autoboxing or runtime type erasure will allow the code to compile with a warning, but Java 17's strict generic type checking enforces a compilation error for such mismatches.
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
✓
Compilation error
The code attempts to add an integer (10) to a `List<String>`, which is a compile-time type mismatch. Java's generics enforce type safety at compile time, so adding an `int` (autoboxed to `Integer`) to a `List<String>` results in a compilation error. The code will not compile, and no runtime execution occurs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Compilation error
Why this is correct
Generics prevent adding an Integer to List<String>.
- ✗
The code compiles and runs successfully
Why it's wrong here
Incompatible types cause compilation error.
- ✗
ClassCastException at runtime
Why it's wrong here
Compilation fails first.
- ✗
Compiler warning, but runs with unchecked operation
Why it's wrong here
It is an error, not a warning.
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Last reviewed: Jun 25, 2026
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