1Z0-829 Java I/O API and Securing Applications Practice Question
A logging framework in Java has been writing logs to a file using a FileWriter with default buffer size. The logs are frequently lost when the application crashes because the buffer is not flushed. Which change ensures that log messages are written immediately without significantly impacting performance?
⚠ Common exam trap
Candidates often confuse FileWriter's lack of an autoFlush option with PrintWriter's autoFlush feature, or they incorrectly assume that disabling buffering (buffer size 0) is a practical solution, when in fact it causes severe performance degradation due to excessive system calls.
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 a PrintWriter wrapping a FileWriter and set autoFlush=true.
A PrintWriter wrapping a FileWriter with autoFlush=true ensures that every println, printf, or format call triggers an automatic flush of the underlying stream. This guarantees log messages are written to disk immediately upon each write, preventing data loss during a crash, while still allowing the FileWriter's internal buffer to aggregate small writes for performance. The autoFlush mechanism in PrintWriter is specifically designed for this use case in Java I/O.
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 a FileWriter with autoFlush=true.
Why it's wrong here
FileWriter does not have an autoFlush constructor; this option is invalid.
- ✗
Set the buffer size to 0 to disable buffering.
Why it's wrong here
Disabling buffering results in a system call per write, severely impacting performance.
- ✓
Use a PrintWriter wrapping a FileWriter and set autoFlush=true.
Why this is correct
PrintWriter with autoFlush provides a balance: messages are flushed after each line, reducing data loss without excessive overhead.
- ✗
Call flush() after every log message.
Why it's wrong here
Explicit flush after each message is similar to disabling buffering; high overhead.
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