Input/Output in Java5 min read

  • Input/Output in Java is used to process the input and produce the output based on the input. An input source may be a network connection or memory bugger or a disk file. Similarly, the output destination may be any physical device. A stream handles all these devices.
  • Stream is a logical entity that either produces or consumes information. Java allows storing and managing data using files. This is known as file processing data into files. Depending on the requirement, files can be read or written either at bytes level or at characters level, or at fields level.
  • File processing includes creating and updating files and manipulating In Java, a record can be represented as an object. Java also allows reading and writing class objects directly.
  • Input/Output in the Java system links streams with physical devices. Java provides a wide range of I / O classes which are defined by java.io

Some of these classes are listed below –

  • The process of reading and writing objects is called object serialization. The file input refers to the flow of data into a program from either keyboard, mouse, memory, disk, network, or even another program.
  • Similarly, the file output refers to the flow of data from a file to either screen, printer, memory, disk, network, or a program.
  • Java stream is nothing but an ordered sequence of data. It is a common characteristic. Java streams are of two types: input stream and output stream.
BufferedWriterBufferedreader
DatalnputstreamDataOutputStream
FileInputStreamFileOutStream
FileWriterFileReader
ObjectInputStreamObjectOutputStream
BufferedInputStreamBufferedOutputStream
StringwriterOutputStreamwriter
Input/Output in Java

Table of Contents

File class

The file class does not operate on stream. It directly deals with files and file systems. That is it describes the properties of the file.

The commonly used File methods are

getname() returns name of the file
getPath() returns path of the file
getparent() returns name of the parent directory
exists()returns true if the file exists
canWrite()returns whether the file is writable
canRead()returns whether the file is readable
isDirectory() returns whether it is a directory
isFile() returns true if called on a file and returns false if called on a directory
renameTo() It is used to rename the file to specified name.
delete() to set the invoking file to read-only
isAbsolute() returns true if the file has an absolute path and returns false if the file path is relative
lastModification() returns date of last modification done in file
length()returns length of file in bytes
setReadOnly() to set the invoking file to read-on. In Java, the directory is a type of file that contains other files and directories.

In Java, 3 streams are created for us automatically. All these streams are attached to the console.

1) System.out: the standard output stream

2) System.in the standard input stream

3) System.err: standard error stream

  1. Stream
    A stream is a sequence of data. In Java, a stream is composed of bytes. It’s called a stream because it’s like a stream of water that continues to flow.
  2. OutputStream
    Java application uses an output stream to write data to a destination, it may be a file, an array, peripheral device, or socket.
  3. InputStream
    Java application uses an input stream to read data from a source, it may be a file, an array, peripheral device, or socket.

Byte stream

  • In Java input stream (byte), InputStream is an abstract class and hence we can not create the object of this class.
  • Some of the commonly used InputStream methods are –
Reading bytes read ( )
Repositioning to the beginning of the stream reset ()
Skipping ahead of a string skip ()
Finding the number of bytes in a stream available available ( )
Closing streams close()
  • Setting the input pointer to the previously set mark: reset(); The base class for output stream (byte) is OutputStream. This is also an abstract class.
  • Some of the commonly used OutputStream methods are
    • Writing byte(s) to o/p stream : write ()
    • Closing output stream : close ()
  • Other classes that implement InputStream and OutputStream are tabulated below with their purpose. These are byte stream classes.
Name Of ClassPurpose
FileInputStream To read bytes from file
FileOutputStream To write bytes to a file
ByteArrayInputStream Uses a byte array as the source
ByteArrayOutputStream Uses a byte array as the destination.
FilteredlnputStream Is the wrapper around the input stream that transparently provides some extended level of functionality
FilteredOutputStream Is the wrapper around the output stream that transparently provides some extended level of functionality.
BufferedInputStream Extends a filtered input class by attaching a memory buffer. This buffer allows java to perform input operations on more than a byte at a time. This is used to increase performance.

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