1Z0-811 Primitives, Strings and Operators Practice Question
A developer needs to concatenate several string values in a loop. Which approach is most efficient for performance?
⚠ Common exam trap
Oracle often tests the misconception that the '+' operator is always optimized by the compiler, but in a loop it creates a new StringBuilder per iteration, making it far less efficient than using a single StringBuilder outside the loop.
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
✓
Using StringBuilder
StringBuilder is the most efficient approach for concatenating strings in a loop because it maintains a mutable sequence of characters, avoiding the creation of intermediate String objects. In contrast, using the '+' operator or String.concat() inside a loop results in the allocation of a new String object for each concatenation, leading to O(n²) time complexity and increased garbage collection overhead.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Using StringBuilder
Why this is correct
Correct: StringBuilder provides mutable sequence and is optimized for such use.
- ✗
Using String.concat()
Why it's wrong here
Incorrect: concat() also creates a new String object each time.
- ✗
Using the '+' operator inside the loop
Why it's wrong here
Incorrect: each '+' creates a new String object, causing memory and performance overhead.
- ✗
Using StringBuffer
Why it's wrong here
Incorrect: StringBuffer is thread-safe but slower than StringBuilder, and StringBuilder is preferred for single-threaded scenarios.
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