I / O类的例外

Question

I'm studying for OCP exam these classes I/O:

• OutputStream subclasses:

  • FileOutputStream
  • BufferedOutputStream
  • DataOutputStream
  • PrintStream (I see its methods write() don't throw exceptions)

• Writer subclasses:

  • FileWriter
  • BufferedWriter
  • PrintWriter (I see its methods write() don't throw exceptions)

• Reader subclasses:

  • FileReader
  • BufferedReader

• InputStream subclasses:

  • BufferedInputStream
  • FilterInputStream
  • ObjectInputStream

My question: For the main methods read and write (with different signatures), when does each of these classes throw the IOException? In the javadoc there is only a phrase:

IOException - if an I/O error occurs

without an explanation about the cases.

I know this (I don't know if these are correct):

• FileOutputStream throws java.io.FileNotFoundException if the file doesn't exist. This class, infact, doesn't create a file;

• FileWriter throws java.io.FileNotFoundException if the file doesn't exist. This class infact, doesn't create a file;

• BufferedReader throws java.nio.file.NoSuchFileException (subclass of IOException), if file doesn't exist;

• FileInputStream throws java.io.FileNotFoundException if the file doesn't exist.

Thanks a lot!

A.

Answer 1

If you google the API documentation for the class, generally the Javadocs will give an explanation of what exceptions are thrown in what circumstances, eg for FileWriter

https://docs.oracle.com/javase/7/docs/api/java/io/FileWriter.html

Answer 2

An I/O exception is thrown by any of these classes when they encounter a problem during execution. The file output streams can throw an exception if :

• File don't exist
• File is read only
• The OS refuses access to the file
• The drive you are writing to dose not have sufficient space

The input streams usually throws exception if :

• The stream is not properly initialised
• The input type is miss matched
• If the file beeing read from is changed while reading
• If the file doesn't exist.