The answer is 20 because the `BufferedReader read()` method, when called in a loop, reads one character at a time and returns its Unicode value, incrementing a counter for each successful read until it returns -1 at the end of the file. This behavior directly counts the total number of characters in the file, which in this case is exactly 20. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your understanding of how `BufferedReader.read()` interacts with file I/O and loop termination conditions, often appearing as a trick where candidates confuse the returned integer value with the character itself or forget that `read()` returns -1 to signal EOF. A common trap is assuming `read()` returns the character count or that the loop counts something other than each individual character. Remember the memory tip: "Read returns the char, not the count; the count comes from the loop."
1Z0-829 Java I/O API and Securing Applications Practice Question
This 1Z0-829 practice question tests your understanding of java i/o api and securing applications. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
Refer to the exhibit.
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(new String("test"));
oos.flush();
byte[] data = baos.toByteArray();
System.out.println(data.length);
Refer to the exhibit.
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(new String("test"));
oos.flush();
byte[] data = baos.toByteArray();
System.out.println(data.length);
A
20
4 header + 6 class desc + 1 blockdata header + 4 length + 4 chars = 19, but padded to 20.
B
4
Why wrong: Only the string length in bytes, but header and metadata are included.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
20
The correct answer is A (20) because the code creates a `BufferedReader` wrapping a `FileReader` for a file containing exactly 20 characters. The `read()` method in a loop reads one character at a time, returning the Unicode value of each character, and the loop increments `count` for each successful read until `read()` returns -1 (end of file). Thus, `count` equals the total number of characters in the file, which is 20.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
20
Why this is correct
4 header + 6 class desc + 1 blockdata header + 4 length + 4 chars = 19, but padded to 20.
Related concept
Read the scenario before looking for a memorised answer.
✗
4
Why it's wrong here
Only the string length in bytes, but header and metadata are included.
✗
16
Why it's wrong here
Missing header and class descriptor.
✗
8
Why it's wrong here
Only header bytes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse `read()` with `read(byte[])` or `read(char[])` methods, which return the number of bytes or characters read in a single call, leading them to incorrectly assume the loop counts fewer iterations than the actual character count.
Detailed technical explanation
How to think about this question
Under the hood, `BufferedReader.read()` reads a single character (2 bytes in Java's internal UTF-16 representation) but returns it as an `int` in the range 0–65535, or -1 at end of stream. The loop increments `count` for each character, so the final value equals the number of characters in the file, regardless of encoding or buffer size. In real-world scenarios, this pattern is used to count characters or process text line-by-line, but developers must remember that `read()` returns a single character, not a chunk size.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 1Z0-829 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Java I/O API and Securing Applications — This question tests Java I/O API and Securing Applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 20 — The correct answer is A (20) because the code creates a `BufferedReader` wrapping a `FileReader` for a file containing exactly 20 characters. The `read()` method in a loop reads one character at a time, returning the Unicode value of each character, and the loop increments `count` for each successful read until `read()` returns -1 (end of file). Thus, `count` equals the total number of characters in the file, which is 20.
What should I do if I get this 1Z0-829 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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