Input Stream and File Input Stream with its methods

InputStream Class:

• Syntax: 
  java.lang.Object
            java.io.InputStream
• This abstract class is the superclass of all classes representing an input stream of bytes.
• Applications that need to define a subclass of InputStream must always provide a method that returns the next byte of input.
• It has one constructor and seven methods.
• Constructor: public InputStream()
• Methods:
• 1. read:
• Syntax:
• public abstract int read() throws IOException
• public int read(byte[] b) throws IOException
• public int read(byte[] b, int off, int len) throws IOException
• Use: 
• Reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned.
• The first byte read is stored into element b[0], the next one into b[1], and so on. 
• The first byte read is stored into element b[off], the next one into b[off+1], and so on.
• Parameters:
• b - the buffer into which the data is read.
• off - the start offset in array b at which the data is written.
• len - the maximum number of bytes to read.
• Returns: the next byte of data, or -1 if the end of the stream is reached.
• Throws:
• IOException - If the first byte cannot be read for any reason other than end of file, or if the input stream has been closed, or if some other I/O error occurs.
• NullPointerException - If b is null.
• IndexOutOfBoundsException - If off is negative, len is negative, or len is greater than b.length - off
• 2. available:
• Syntax: public int available() throws IOException
• Use: Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream.
• Returns: an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking or 0 when it reaches the end of the input stream.
• Throws: IOException - if an I/O error occurs.
• 3. close:
• Syntax: public void close() throws IOException
• Use: Closes this input stream and releases any system resources associated with the stream. The close method of InputStream does nothing.
• Throws: IOException - if an I/O error occurs.
• 4. mark:
• Syntax: public void mark(int readlimit)
• Use: Marks the current position in this input stream. A subsequent call to the reset method repositions this stream at the last marked position so that subsequent reads re-read the same bytes. The mark method of InputStream does nothing.
• Parameters: readlimit - the maximum limit of bytes that can be read before the mark position becomes invalid.
• 5. markSupported:
• Syntax: public boolean markSupported()
• Use: Tests if this input stream supports the mark and reset methods. Whether or not mark and reset are supported is an invariant property of a particular input stream instance. The markSupported method of InputStream returns false.
• Returns: true if this stream instance supports the mark and reset methods; false otherwise.
• 6. reset:
• Syntax: public void reset() throws IOException
• Use: Repositions this stream to the position at the time the mark method was last called on this input stream.
• Throws: IOException - if this stream has not been marked or if the mark has been invalidated.
• 7. skip:
• Syntax: public long skip(long n) throws IOException
• Use: Skips over and discards n bytes of data from this input stream.
• Parameters: n - the number of bytes to be skipped.
• Returns: the actual number of bytes skipped.
• Throws: IOException - if the stream does not support seek, or if some other I/O error occurs.

FileInputStream Class:

• Syntax: 

           java.lang.Object
                   java.io.InputStream
                           java.io.FileInputStream

• A FileInputStream obtains input bytes from a file in a file system. 
• FileInputStream is meant for reading streams of raw bytes such as image data.
• It has three constructors and seven methods.
• Constructor: 
• Syntax:
• public FileInputStream(File file) throws FileNotFoundException
• public FileInputStream(FileDescriptor fdObj)
• public FileInputStream(String name) throws FileNotFoundException
• Use:
• Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system.
• Creates a FileInputStream by using the file descriptor fdObj, which represents an existing connection to an actual file in the file system.
• Parameters:
• file - the file to be opened for reading.
• fdObj - the file descriptor to be opened for reading.
• Throws:
• FileNotFoundException - if the file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading.
• SecurityException - if a security manager exists and its checked method denies read access to the file.
• Methods:
• 1. available:
• It is an overridden method from the InputStream class.
• Note: for more details: See InputStream Class (Methods: 02)
• 2. close:
• It is an overridden method from the InputStream class.
• Note: for more details: See InputStream Class (Methods: 03)
• 3. finalize:
• Syntax: protected void finalize() throws IOException
• Use: Ensures that the close method of this file input stream is called when there are no more references to it.
• Overrides: finalize in class Object
• Throws: IOException - if an I/O error occurs.
• 4. getChannel:
• Syntax: public FileChannel getChannel()
• Use: Returns the unique FileChannel object associated with this file input stream.
• Returns: the file channel associated with this file input stream
• 5. getFD
  • Syntax: public final FileDescriptor getFD() throws IOException
  • Use: Returns the FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream.
  • Returns: the file descriptor object associated with this stream.
• Throws: IOException - if an I/O error occurs.
• 6. read
• It is an overridden method from the InputStream class.
• Note: for more details: See InputStream Class (Methods: 01)
• 7. skip
• It is an overridden method from the InputStream class.
• Note: for more details: See InputStream Class (Methods: 07)

Example (Read File):

• Step 01: Create a .txt file.
  
• Step 02: Write a JAVA program.
  
• Step 03: Enjoy the Output.