Java Streams

Java programs perform Input Output (I/O) through the streams. A stream is an abstraction that either produces or consumes the information.

A stream is linked to a physical device by the Java I/O system.

All the streams behave in the same manner, even if the actual physical devices to which they are linked differ. Thus, the same I/O classes and the methods can be applied to the different types of devices. This means that an input stream can abstract many different kinds of input, from a keyboard, a disk file, or a network socket. Likewise, an output stream may refer to the console, a disk file, or a network connection. Streams are a clean way to deal with input/output without having every part of your code understand the difference between a keyboard and a network, for example. Java implements the streams within class hierarchies defined in the java.io package.

Types of Stream

Java defines the following two types of streams :

Byte streams
Character streams

Java Byte Stream

The Byte streams provide a convenient means for handling input and output of bytes. Byte streams are used, for example, when reading or writing binary data.

Byte streams are defined by using two hierarchies. At the top are the following two abstract classes :

InputStream
OutputStream

Each of these abstract classes has several concrete subclasses that handle the differences among the various devices, such as disk files, network connections, and even memory buffers.

The byte stream classes in the java.io package are shown in the Following table :

Remember - To use the stream classes, you must import the java.io package.

Stream Class	Meaning
BufferedInputStream	Buffered input stream
BufferedOutputStream	Buffered output stream
ByteArrayInputStream	Input stream that reads from a byte array
ByteArrayOutputStream	Output stream that writes to a byte array
DataInputStream	An input stream that contains the methods for reading the Java standard data types
DataOutputStream	An output stream that contains the methods for writing the Java standard data types
FileInputStream	Input stream that reads from a file
FileOutputStream	Output stream that writes to a file
FilterInputStream	Implements InputStream
FilterOutputStream	Implements OutputStream
InputStream	Abstract class that describes stream input
ObjectInputStream	Input stream for objects
ObjectOutputStream	Output stream for objects
OutputStream	Abstract class that describes stream output
PipedInputStream	Input pipe
PipedOutputStream	Output pipe
PrintStream	Output stream that contains the print() and println()
PushbackInputStream	Input stream that supports one-byte "unget", which returns a byte to the input stream
SequenceInputStream	Input stream that is a combination of two or more input streams that will be read sequentially, one after the other

The abstract classes, InputStream and OutputStream define several key methods that the other stream classes implement. Two of the most important are read() and write() methods, respectively, which read and write bytes of data. Each has a form that is abstract and must be overridden by the derived stream classes.

Java Character Stream

The Character stream provide a convenient means for handling input and output of characters. They are Unicode and, therefore, can be internationalized. Also, in some cases, character streams are more efficient than the byte streams.

Character streams are defined by using the two class hierarchies. At the top are two abstract classes :

Reader
Writer

These abstract classes handle the Unicode character streams.

Java has several concrete subclasses of each of these. The character stream classes in the java.io package are shown in the following table :

String Class	Meaning
BufferedReader	Buffered input character stream
BufferedWriter	Buffered output character stream
CharArrayReader	Input stream that reads from a character array
CharArrayWriter	Output stream that writes to a character array
FileReader	Input stream that reads from a file
FileWriter	Output stream that writes to a file
FilterReader	Filtered reader
FilterWriter	Filtered writer
InputStreamReader	Input stream that translates bytes to characters
LineNumberReader	Input stream that counts lines
OutputStreamWriter	Output stream that translates characters to bytes
PipedReader	Input pipe
PipedWriter	Output pipe
PrintWriter	Output stream that contains the print() and println()
PushbackReader	Input stream that allows the character to be returned to the input stream
Reader	Abstract class that describes the character stream input
StringReader	Input stream that reads from a string
StringWriter	Output stream that writes to a string
Writer	Abstract class that describes the character stream output

The abstract classes, Reader and Writer define several key methods that the other stream classes implement. Two of the most important methods are read() and write(), which read and write the characters of data, respectively. Each has a form that is abstract and must be overridden by the derived stream classes.

Java Predefined Streams

As you already know, all Java programs automatically import the java.lang package. This package defines a class called System, which encapsulates several aspects of run-time environment. For example, using some of its methods, you can obtain the current time and settings of the various properties associates with the system.

System also contains the following three predefined stream variables:

in - System.in refers to the standard input, which is the keyboard by default
out - System.out refers to the standard output stream. By default, this is the console
err - System.err refers to the standard error stream, which also is the console by default.

However, these streams may be redirected to any compatible I/O devices.

These fields are declared as public, static, and final within System. This means that they can be used by any other part of your program and without reference to a specific System object.

System.in is an object of type InputStream, System.out and System.err are objects of type PrintStream. These are the byte streams, even though they are typically used to read and write the characters from and to the console. As you will see, you can wrap these within the character-based streams, if desired.

Examples on Files in Java

Here are some examples related to files in Java, you can go for.

Java Online Test

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