Java File and Stream Handling

Study Notes

Data stored in variables and arrays is temporary and lost when a program terminates or a local variable goes out of scope.
Computers use files for long-term retention of data, which exists beyond the duration of program execution.
Files are stored on secondary storage devices such as hard disks, optical disks, flash drives, and magnetic tapes.

Java views each file as a sequential stream of bytes.
A file stream can be used to input and output data as bytes or characters.
Streams that input and output bytes are known as byte-based streams, representing data in its binary format.
Streams that input and output characters are known as character-based streams, representing data as a sequence of characters.
Files created using byte-based streams are referred to as binary files, while files created using character-based streams are referred to as text files.
A Java program opens a file by creating an object and associating a stream of bytes or characters with it.
Java creates three stream objects when a program begins executing: System.in, System.out, and System.err.

Class File provides information about files and directories.
Class File provides four constructors to specify the name of a file or directory to associate with the File object.
The constructor with a String argument specifies the name of a file or directory, which can contain path information.
The constructor with two String arguments specifies an absolute or relative path and the file or directory to associate with the File object.
The constructor with File and String arguments uses an existing File object that specifies the parent directory of the file or directory specified by the String argument.
The fourth constructor uses a URI object to locate the file.

Sequential-access files store records in order by the record-key field.
Text files are human-readable files.
Java imposes no structure on a file, and notions such as records do not exist as part of the Java language.
You must structure files to meet the requirements of your applications.

Formatter outputs formatted Strings to the specified stream.
The constructor with one String argument receives the name of the file, including its path.
If a path is not specified, the JVM assumes that the file is in the directory from which the program was executed.
If the file does not exist, it will be created. If an existing file is opened, its contents are truncated.
A SecurityException occurs if the user does not have permission to write data to the file.
A FileNotFoundException occurs if the file does not exist and a new file cannot be created.

Scanner method hasNext determines whether the end-of-file key combination has been entered.
A NoSuchElementException occurs if the data being read by a Scanner method is in the wrong format or if there is no more data to input.
Formatter method format works like System.out.printf.
A FormatterClosedException occurs if the Formatter is closed when you attempt to output.
Formatter method close closes the file.