Input and output

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The Java library classes for IO are divided by input and output, as you can see by looking at the online Java class hierarchy with your Web browser. By inheritance, all classes derived from InputStream have basic methods called read( ) for reading a single byte or array of bytes. Likewise, all classes derived from OutputStream have basic methods called write( ) for writing a single byte or array of bytes. However, you won’t generally use these methods; they exist so more sophisticated classes can use them as they provide a more useful interface. Thus, you’ll rarely create your stream object by using a single class, but instead will layer multiple objects together to provide your desired functionality. The fact that you create more than one object to create a single resulting stream is the primary reason that Java’s stream library is confusing.

Types of InputStream

InputStream’s job is to represent classes that produce input from different sources. These sources can be (and each has an associated subclass of InputStream):

  1. An array of bytes
  2. A String object
  3. A file
  4. A “pipe,” which works like a physical pipe: you put things in one end and they come out the other
  5. A sequence of other streams, so you can collect them together into a single stream
  6. Other sources, such as an Internet connection. (This will be discussed in a later chapter.)
Class

Function

Constructor Arguments

How to use it

ByteArray-InputStream

Allows a buffer in memory to be used as an InputStream.

The buffer from which to extract the bytes.

As a source of data. Connect it to a FilterInputStream object to provide a useful interface.

StringBuffer-InputStream

Converts a String into an InputStream.

A String. The underlying implementation actually uses a StringBuffer.

As a source of data. Connect it to a FilterInputStream object to provide a useful interface.

File-InputStream

For reading information from a file.

A String representing the file name, or a File or FileDescriptor object.

As a source of data. Connect it to a FilterInputStream object to provide a useful interface.

Piped-InputStream

Produces the data that’s being written to the associated PipedOutput-Stream. Implements the “piping” concept.

PipedOutputStream

As a source of data in multithreading. Connect it to a FilterInputStream object to provide a useful interface.

Sequence-InputStream

Coverts two or more InputStream objects into a single InputStream.

Two InputStream objects or an Enumeration for a container of InputStream objects.

As a source of data. Connect it to a FilterInputStream object to provide a useful interface.

Filter-InputStream

Abstract class which is an interface for decorators that provide useful functionality to the other InputStream classes. See Table 10-3.

See Table 10-3.

See Table 10-3.

Types of OutputStream

Class

Function

Constructor Arguments

How to use it

ByteArray-OutputStream

Creates a buffer in memory. All the data that you send to the stream is placed in this buffer.

Optional initial size of the buffer.

To designate the destination of your data. Connect it to a FilterOutputStream object to provide a useful interface.

File-OutputStream

For sending information to a file.

A String representing the file name, or a File or FileDescriptor object.

To designate the destination of your data. Connect it to a FilterOutputStream object to provide a useful interface.

Piped-OutputStream

Any information you write to this automatically ends up as input for the associated PipedInput-Stream. Implements the “piping” concept.

PipedInputStream

To designate the destination of your data for multithreading. Connect it to a FilterOutputStream object to provide a useful interface.

Filter-OutputStream

Abstract class which is an interface for decorators that provide useful functionality to the other OutputStream classes. See Table

10-4.

See Table 10-4.

See Table 10-4.



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