I/O Operations Flashcards

What is the output of `System.out.printf("%05.2f", 3.7)` ?

Answer: "03.70"

`%05.2f` formats to total width 5, 2 decimal places, zero-padded, producing `03.70`.

Which `PrintWriter` constructor automatically flushes the buffer after every `println`, `printf`, or `format` call?

Answer: Both A and C

Passing `true` as the auto-flush argument to either the `Writer` or `OutputStream` constructor enables auto-flush on line-terminating methods.

What does `DataInputStream.readUTF()` expect about the byte stream format?

Answer: A 2-byte length prefix followed by modified UTF-8 encoded bytes

`readUTF` reads a 2-byte big-endian length then the modified UTF-8 bytes, matching the format written by `DataOutputStream.writeUTF`.

Which NIO.2 attribute view provides access to POSIX file permissions?

Answer: PosixFileAttributeView

`PosixFileAttributeView` exposes owner, group, and permission bits on POSIX-compliant filesystems.

What is the default behavior of `Files.copy(InputStream in, Path target)` if the target file already exists?

Answer: It throws `FileAlreadyExistsException`

Without `REPLACE_EXISTING`, `Files.copy` fails with `FileAlreadyExistsException` to avoid silent data loss.

Which method on `BufferedWriter` writes a platform-dependent newline?

Answer: newLine()

`BufferedWriter.newLine()` writes the system property `line.separator`, making output portable across platforms.

What does calling `mark(readAheadLimit)` on a `BufferedInputStream` allow you to do?

Answer: Reset the stream position back to the marked point after reading up to `readAheadLimit` bytes

`mark` saves the current position; `reset` returns to it as long as no more than `readAheadLimit` bytes have been read since the mark.