OCP 17 Exam - chapter 14 notes - I/O

Streams

• byte streams are called *InputStream/*OutputStream, where character streams are *Reader/*Writer

• exceptions are PrintWriter and PrintStream

• exam my trick us by wrapping Writer/Reader into Input/OutputStream or wrapping InputStream into OutputStream

• be aware that not all readers support mark(int), so program might for some readers throw IOException

IO

• it might be tricky that File has constructor with parent and child, e.g. new File(new File("/root"), "/user/.bashrc") (Q.15)

NIO.2

• memorize creating Path: Path.of, Paths.get, FileSystem.getPath (Q.10)

• be aware that Path#toRealPath might throw NoSuchFileException (Q.23)

• Files.readAllLines returns List, while Files.lines returns Stream (Q.8)

• be aware that most of Files methods throws IOException, so questions might hide compilation error when IOException is not handled (Q.4)

• both methods Files.walk and Files.find returns Stream<Path>, but for Files.find we can provide path and attribute filter as method parameter (Q.5)

• to create directory we should use Files.createDirectory (to avoid exception when no parent, use Files.createDirectories)

System console

• System.console might return null if not available (Q.3)

Playground code

https://github.com/RG9/rg-playground-ocp17/tree/main/Chapter14/src/test/java/pl/rg9/demo

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Credit: OCP Oracle Certified Professional Java SE 17 Developer Study Guide