Using the Streams

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Trail: Essential Java Classes
Lesson: I/O

Using the Streams

The following table lists java.io's streams and describes what they do. Note that many times, java.io contains character streams and byte streams that perform the same type of I/O but for different data types.

I/O Streams
Type of I/O Streams Description

Memory
CharArrayReader CharArrayWriter

ByteArrayInputStream ByteArrayOutputStream
Use these streams to read from and write to memory. You create these streams on an existing array and then use the read and write methods to read from or write to the array.

StringReader StringWriter

StringBufferInputStream

Use StringReader to read characters from a String in memory. Use StringWriter to write to a String. StringWriter collects the characters written to it in a StringBuffer, which can then be converted to a String.

StringBufferInputStream is similar to StringReader, except that it reads bytes from a StringBuffer.

Pipe
PipedReader PipedWriter

PipedInputStream PipedOutputStream

Implement the input and output components of a pipe. Pipes are used to channel the output from one thread into the input of another. See PipedReader and PipedWriter in action in the section How to Use Pipe Streams.

File

FileReader FileWriter

FileInputStream FileOutputStream

Collectively called file streams, these streams are used to read from or write to a file on the native file system. The section How to Use File Streams. has an example that uses FileReader and FileWriter to copy the contents of one file into another.

Concatenation

N/A

SequenceInputStream

Concatenates multiple input streams into one input stream. The section How to Concatenate Files. has a short example of this class.

Object
Serialization

N/A

ObjectInputStream ObjectOutputStream

Used to serialize objects. See Object Serialization.

Data
Conversion

N/A

DataInputStream DataOutputStream

Read or write primitive data types in a machine-independent format. See How to Use DataInputStream and DataOutputStream. shows an example of using these two streams.

Counting

LineNumberReader

LineNumberInputStream

Keeps track of line numbers while reading.

Peeking Ahead

PushbackReader

PushbackInputStream

These input streams each have a pushback buffer. When reading data from a stream, it is sometimes useful to peek at the next few bytes or characters in the stream to decide what to do next.

Printing

PrintWriter

PrintStream

Contain convenient printing methods. These are the easiest streams to write to, so you will often see other writable streams wrapped in one of these.

Buffering

BufferedReader BufferedWriter

BufferedInputStream BufferedOutputStream

Buffer data while reading or writing, thereby reducing the number of accesses required on the original data source. Buffered streams are typically more efficient than similar nonbuffered streams and are often used with other streams.

Filtering

FilterReader FilterWriter

FilterInputStream FilterOutputStream

These abstract classes define the interface for filter streams, which filter data as it's being read or written. The section Working with Filter Streams shows you how to use filter streams and how to implement your own.

Converting between Bytes and Characters

InputStreamReader OutputStreamWriter

A reader and writer pair that forms the bridge between byte streams and character streams.

An InputStreamReader reads bytes from an InputStream and converts them to characters, using the default character encoding or a character encoding specified by name.

An OutputStreamWriter converts characters to bytes, using the default character encoding or a character encoding specified by name and then writes those bytes to an OutputStream.

You can get the name of the default character encoding by calling System.getProperty("file.encoding").

The next several sections provide examples on how to use several of these streams:

How to Use File Streams

How to Use Pipe Streams

How to Wrap a Stream

How to Concatenate Files

Working with Filter Streams

I/O Streams
Type of I/O	Streams	Description
Memory	`CharArrayReader CharArrayWriter` `ByteArrayInputStream ByteArrayOutputStream`	Use these streams to read from and write to memory. You create these streams on an existing array and then use the read and write methods to read from or write to the array.
`StringReader StringWriter` `StringBufferInputStream`	`Use StringReader` to read characters from a `String` in memory. Use `StringWriter` to write to a `String`. `StringWriter` collects the characters written to it in a `StringBuffer`, which can then be converted to a `String`. `StringBufferInputStream` is similar to `StringReader`, except that it reads bytes from a `StringBuffer`.
Pipe	`PipedReader PipedWriter` `PipedInputStream PipedOutputStream`	Implement the input and output components of a pipe. Pipes are used to channel the output from one thread into the input of another. See `PipedReader` and `PipedWriter` in action in the section How to Use Pipe Streams.
File	`FileReader FileWriter` `FileInputStream FileOutputStream`	Collectively called file streams, these streams are used to read from or write to a file on the native file system. The section How to Use File Streams. has an example that uses `FileReader` and `FileWriter` to copy the contents of one file into another.
Concatenation	N/A `SequenceInputStream`	Concatenates multiple input streams into one input stream. The section How to Concatenate Files. has a short example of this class.
Object Serialization	N/A `ObjectInputStream ObjectOutputStream`	Used to serialize objects. See Object Serialization.
Data Conversion	`N/A` `DataInputStream DataOutputStream`	Read or write primitive data types in a machine-independent format. See How to Use DataInputStream and DataOutputStream. shows an example of using these two streams.
Counting	`LineNumberReader` `LineNumberInputStream`	Keeps track of line numbers while reading.
Peeking Ahead	`PushbackReader` `PushbackInputStream`	These input streams each have a pushback buffer. When reading data from a stream, it is sometimes useful to peek at the next few bytes or characters in the stream to decide what to do next.
Printing	`PrintWriter` `PrintStream`	Contain convenient printing methods. These are the easiest streams to write to, so you will often see other writable streams wrapped in one of these.
Buffering	`BufferedReader BufferedWriter` `BufferedInputStream BufferedOutputStream`	Buffer data while reading or writing, thereby reducing the number of accesses required on the original data source. Buffered streams are typically more efficient than similar nonbuffered streams and are often used with other streams.
Filtering	`FilterReader FilterWriter` `FilterInputStream FilterOutputStream`	These abstract classes define the interface for filter streams, which filter data as it's being read or written. The section Working with Filter Streams shows you how to use filter streams and how to implement your own.
Converting between Bytes and Characters	`InputStreamReader OutputStreamWriter`	A reader and writer pair that forms the bridge between byte streams and character streams. An `InputStreamReader` reads bytes from an `InputStream` and converts them to characters, using the default character encoding or a character encoding specified by name. An `OutputStreamWriter` converts characters to bytes, using the default character encoding or a character encoding specified by name and then writes those bytes to an `OutputStream`. You can get the name of the default character encoding by calling `System.getProperty("file.encoding")`.

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