Java input output package
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The java.io package contains classes for input and output in Java. It includes abstract classes like InputStream, OutputStream, Reader, and Writer as well as concrete subclasses like FileInputStream, FileOutputStream, BufferedReader, and PrintWriter. The classes use decorator patterns and handle byte streams for binary data and character streams for text. Exceptions like IOException must be caught when using these classes to ensure resources are properly closed.
Java input output package
- 1. java.io Package Sujit Kumar Zenolocity LLC Copyright 2012-2024 @
- 2. java.io Package • The java.io package contains a fairly large number of classes that deal with Java input & output. Most of the classes consist of: • Byte streams : that are subclasses of the abstract classes InputStream or OutputStream • Character streams : that are subclasses of the abstract classes Reader and Writer • The methods for reading & writing data from byte streams and character streams are similar.
- 3. java.io Package (contd…) • The Reader and Writer classes read and write 16-bit Unicode characters. • The InputStream and OutputStream classes read and write 8-bit bytes respectively. • Derived classes of the above 4 abstract classes add additional responsibilities using the Decorator pattern.
- 4. How to choose the correct implementation (derived class)? • • • • What is your format: text or binary ? Do you want random access to a file ? Are you using objects or non-objects ? What are your sources and sinks of data (like sockets, files, strings or array of characters) ? • Do you need to use filtering techniques like buffering, checksumming ?
- 5. Byte Stream Abstract Classes InputStream — byte reader • • • • read() a single byte or an array of bytes skip() bytes mark() and reset() position close() the stream (always in finally block) OutputStream —byte writer • write() a single byte or an array of bytes • flush() the stream (in case it is buffered) • close() the stream (always in finally block)
- 6. Character Stream Abstract Classes Reader — character reader • • • • read() a single char or into a char array skip() chars mark() and reset() position close() the stream (always in finally block) Writer — character writer • write() a single char or from a char array • flush() the stream (in case it is buffered) • close() the stream (always in finally block)
- 7. Byte Stream Concrete classes • • • • • • • • FileInputStream, FileOutputStream BufferedInputStream, BufferedOutputStream ByteArrayInputStream, ByteArrayOutputStream DataInputStream, DataOutputStream FilterInputStream, FilterOutputStream ObjectInputStream, ObjectOutputStream PipedInputStream, PipedOutputStream LineNumberInputStream • PrintStream
- 8. Character Stream Concrete classes • • • • • • • • FileReader, FileWriter BufferedReader, BufferedWriter CharArrayReader, CharArrayWriter InputStreamReader, InputStreamWriter FilterReader, FilterWriter ObjectReader, ObjectWriter PipedReader, PipedWriter StringReader, StringWriter • LineNumberReader • PrintWriter
- 9. Applying the Decorator Pattern • Example: Read each line from a file • BufferedReader => InputStreamReader => FileInputStream • Wrap an InputStreamReader over a FileInputStream. • Then, wrap a BufferedReader over the InputStreamReader.
- 10. Applying the Decorator Pattern (contd…) • BufferedReader => Reads text from a characterinput stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines. • FileInputStream => obtains input bytes from a file in a file system. • InputStreamReader => bridge from byte streams to character streams. It reads bytes and decodes them into characters using a specified charset.
- 11. Exception Handling • The constructors and methods of I/O classes can throw a checked exception. • The base class for I/O exceptions is java.io.IOException. Some methods can throw a subclass of IOException. For example, the constructors of FileInputStream, FileOutputStream and FileReader can throw FileNotFoundException. • The call to close() should always occur in a finally block (ensures that the I/O channel is closed properly even if an exception occurs).