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3.2 Reading & Writing FilesHomepage  « Java5 Certification « 3.2 Reading & Writing Files

In this lesson we investigate how we can use classes within the java.io package to read from files, write to files and use the BufferedReader, BufferedWriter, File, FileReader, FileWriter and PrintWriter sometimes in unison to create a software solution.

Lets take a look at the points outlined at the Oracle Website for this part of the certification.

• Section 3: API Contents
  
  
  • Given a scenario involving navigating file systems, reading from files, or writing to files, develop the correct solution using the following classes (sometimes in combination), from java.io: BufferedReader,BufferedWriter, File, FileReader, FileWriter and PrintWriter.

Character Streams Top

Character streams are defined within two class hierarchies, one for input and one for output:

• The Writer class is the abstract superclass of all character output streams
• The Reader class is the abstract superclass of all character input streams

These classes define the characteristics that are common to character input and character output streams, which are implemented in the concrete subclasses of each hierarchy.

Character Output Stream Hierarchy Top

The diagram below shows the classes in the character output stream hierarchy of which the Writer class is the abstract superclass.:

Class	Description
Writer	Abstract character stream superclass which describes this type of output stream.
BufferedWriter	Buffered output character stream.
CharArrayWriter	Character buffer output stream.
FilterWriter	Abstract character stream for writing filtered streams.
OuputStreamWriter	Output Stream that acts as a bridge for encoding byte streams from character streams.
FileWriter	Output stream for writing characters to a file.
PipedWriter	Piped character output stream.
PrintWriter	Convenience output character stream to add functionality to another stream, an example being to print to the console using print() and println().
StringWriter	Output stream for writing characters to a string.

Click on one of the class links in the table above to see usage for the character output streams required for certification.

Character Input Stream Hierarchy Top

The diagram below shows the classes in the character input stream hierarchy of which the Reader class is the abstract superclass.:

Class	Description
Reader	Abstract character stream superclass which describes this type of input stream.
BufferedReader	Buffered input character stream.
LineNumberReader	Input character stream that keeps a count of line numbers.
CharArrayReader	Character buffer input stream.
FilterReader	Abstract character stream for reading filtered streams.
PushbackReader	Character stream reader containing functionality to return characters to the input stream.
InputStreamReader	Input Stream that acts as a bridge for decoding byte streams into character streams.
FileReader	Input stream for reading characters from a file.
PipedReader	Piped character input stream.
StringReader	Input stream for reading characters from a string.

Click on one of the class links in the table above to see usage for the character input streams required for certification.

Other Java I/O Classes Top

The diagram below shows some other pertinent classes in the java.io package not covered in the byte and character streams above:

Class	Description
File	Abstract representation of file and directory pathnames.
FileDescriptor	Opaque handle to the underlying machine-specific structure.
RandomAccessFile	Allows reading and writing of bytes to a random access file.
StreamTokenizer	Input stream to be parsed into 'tokens'.

Click on the class link in the table above to see usage for the File class required for certification.

The java.io.File Class Top

We will finish this lesson with a talk about the File class that exists within the Java.io package and how we use objects of this class to represent an actual file and directory pathname that may or may not exist already on a hard drive. A File object doesn't contain the file in question or any data associated with the file, it just acts like a pointer to said file and can be a relative or absolute pathname:

1. Relative URL - The common use of a relative URL is by omitting the protocol and server name, as documents generally reside on the same server. So this would be directoryName/fileName.extension.
   For example the relative url images/j5icon.jpg
2. Absolute URL - An absolute url is the complete address of the resource.
   For example the absolute url http://java5tutor.info/images/j5icon.jpg

Related Java5 Tutorials

API Contents - The java.io.File Class
API Contents - The java.io.PrintWriter Class
API Contents - The java.io.BufferedReader Class
API Contents - The java.io.FileReader Class
API Contents - The java.io.BufferedWriter Class
API Contents - The java.io.FileWriter Class

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