Java Stream Classes

Most classes that work directly with streams are part of the java.io package. There are also a few streams classes in java.util.zip. A stream is a sequence of data. The Java I/O stream is an abstraction of a data source or a data destination and represents an object that can produce data or receive data.
An input stream is used to read data from a data source and an output stream is used to write data to a data destination. Just as a stream of water represents a continuous flow of water, a Java stream produces or consumes a continuous flow of data. I/O streams are used to move data from a data source to a Java program, and from a Java program to a data destination.

1. An input stream enables you to read data from a data source to a Java application.
2. An output stream enables you to write data from a Java application to a data destination.

The java.util.zip package contains four input stream classes that read data in a compressed format and return it in uncompressed format and four output stream classes that read data in uncompressed format and write in compressed format.
The two main classes are

1. java.io.InputStream and
2. java.io.OutputStream

Abstract base Classes

These are abstract base classes for many different subclasses with more-specialized abilities.
Although InputStream and OutputStream are abstract classes, many methods in the class library are only specified to return an InputStream or OutputStream, the not more-specific subclass.

Although InputStream and OutputStream are abstract classes, many methods in the class library are only specified to return an InputStream or OutputStream, not the more-specific subclass. For example, this is the signature for the openStream() method in

java.net.URL

:

public final InputStream openStream()
 throws IOException

Channels serve as conduits to I/O services. I/O falls into two broad categories:

1. file I/O and
2. stream I/O.

It is no surprise that there are two types of channels: 1) file and 2) socket.
There is one FileChannel class and three socket channel classes:

1. SocketChannel,
2. ServerSocketChannel, and
3. DatagramChannel.

Channels can be created in several ways. The socket channels have factory methods to create new socket channels directly. But a FileChannel object can be obtained only by calling the getChannel() method on an open RandomAccessFile, FileInputStream, or FileOutputStream object.
You cannot create a FileChannel object directly. File and socket channels are discussed detail in upcoming sections.

SocketChannel sc = SocketChannel.open();
sc.connect (new InetSocketAddress ("somehost", someport));
ServerSocketChannel ssc = ServerSocketChannel.open();
ssc.socket().bind (new InetSocketAddress (somelocalport));
DatagramChannel dc = DatagramChannel.open();
RandomAccessFile raf = new RandomAccessFile ("somefile", "r");
FileChannel fc = raf.getChannel();

The socket classes of java.net have new getChannel() methods as well. While these methods return a corresponding socket channel object, they are not sources of new channels as RandomAccessFile.getChannel() is. They return the channel associated with a socket if one already exists; they never create new channels.

The ByteArrayOutputStream class writes data into the successive components of a byte array using the methods of java.io.OutputStream :

public class ByteArrayOutputStream extends OutputStream

java.io.InputStream

Stream Basics Quiz