Section 11 : The java.io Package

Write appropriate code to read, write and update files using FileInputStream, FileOutputStream, and RandomAccessFile objects.

FileInputStream

Extends InputStream.

Constructors:

FileInputStream (File file)

Creates a FileInputStream object by opening a connection to an actual file, the file named by the File object in the file system. A new FileDescriptor object is created to represent this file connection. Throws FileNotFoundException if the file does not exist, is a directory or for some other reason cannot be opened for reading. Throws SecurityException if access is denied by SecurityManager.

FileInputStream (FileDescriptor fdObj)

Creates a FileInputStream object by using fdObj, which represents an existing connection to an actual file. Throws NullPointerException if fdObj is null. Throws SecurityException if read access is denied.

FileInputStream (String name)

Creates a FileInputStream object by opening a connection to an actual file, the file named by the path-name String name. A new FileDescriptor object is created to represent this file connection. Throws FileNotFoundException if the file does not exist, is a directory or for some other reason cannot be opened for reading. Throws SecurityException if access is denied by SecurityManager.

Methods:

int available ()
void close ()
protected void finalize ()

Ensures that close() is called at the time of garbage collection.

FileDescriptor getFD ()
int read ()
int read (byte [] b)

This method blocks until some input is available.

int read (byte [] b, int offset, int length)
long skip (long n)

This method may, for a variety of reasons, end up skipping a smaller number of bytes, possibly zero. Returns actual number of bytes skipped.

This class does not override mark() and reset().

FileOutputStream

Extends OutputStream. It writes data to a file or a FileDescriptor. Whether or not a file is available or may be created depends upon the underlying platform.

Constructors:

FileOutputStream (File f)

Creates a file output stream to write to the file represented by the specified File object.

FileOutputStream (FileDescriptor fdObj)

Creates an output file stream to write to the specified file descriptor, which represents an existing connection to an actual file in the file system.

FileOutputStream (String name)

Creates an output file stream to write to the file with the specified name. A new FileDescriptor object is created to represent this file connection.

FileOutputStream (String name, boolean append)

Creates an output file stream to write to the file with the specified name. If the second argument is true, then bytes will be written to the end of the file rather than the beginning. A new FileDescriptor object is created to represent this file connection.

Constructors 1,3 and 4 throw FileNotFoundException if the file exists but is a directory rather than a regular file, does not exist but cannot be created, or cannot be opened for any other reason.

Methods: Overrides those in OutputStream.

RandomAccessFile

Extends object, implements DataInput and DataOutput.

A random access file behaves like a large array of bytes stored in the file system. For all the reading routines in the class if end-of-file is reached before the desired number of bytes has been read, an EOFException is thrown. If any byte cannot be read for any reason other than end of file, an IOException other than EOFException is thrown.

No method of this class throws IllegalArgumentException.

Constructors:

RandomAccessFile (File f, String mode)
RandomAccessFile (String name, String mode)

The mode argument must either be equal to “r” or “rw”, indicating that the file is to be opened for input only or for both input and output, respectively. The write methods on this object will always throw an IOException if the file is opened with a mode of “r”. If the mode is “rw” and the file does not exist, then an attempt is made to create it. An IOException is thrown if the file argument refers to a directory. These constructors will throw IllegalArgumentException if mode is not “r” or “rw”. If file exists but is a directory, or cannot be opened or created for any other reason.

Methods:

void close ()
long length ()
int read ()

Reads a byte which is returned as an integer in the range of 0 to 255. method blocks if no onput is available.

int read (byte [] b)
int read (byte [] b, int offset, int length)
FileDescriptor getFD()
long getFilePointer ()

Returns the current offset in this file.

type readType ()

type is java primitive type (all 8 types). The method readBoolean () reads a single byte. A value of

0 represents false. All other values represent true.

void readFully (byte [] b)
void readFully (byte [] b, int offset, int length)

Both of the above methods block until the requested number of bytes are read, the end of stream is detected or exception thrown.

String readLine ()

Does not support the full Unicode character set. This method successively reads the bytes from the file, starting at the current file pointer, until it reaches a line terminator or end of file. Each byte is converted to a character by taking the byte’s value for the lower eight bits of the character and setting the high eight bits to zero. This method blocks for input.

int readUnsignedByte ()
int readUnsignedShort ()
String readUTF ()
void seek (long position)

The offset may be set beyond the end of file. This does not change the length of the file. The file length changes only by writing after the offset has been set beyond the end of the file. If ‘position’ is less than zero, IOException is thrown.

void setLength (long newLength)
int skipBytes (int n)

It may skip over smaller number of bytes (even zero). This method never throws an EOFException. If n is negative, no bytes are skipped.

void write (int b)
void write (byte [] b)
void write (byte [] b, int offset, int length)
void writeByte (int b)
void writeBytes (String s)
void writeChar ( int v)
void writeChars (String s)
void writeDouble (double d)
void writeFloat (float f)
void writeInt (int v)
void writeLong (long l)
void writeShort (int s)
void writeUTF (String s)

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