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Trail: Essential Java Classes
Lesson: I/O: Reading and Writing (but no 'rithmetic)

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:


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