InputStreamReader

AI-generated Key Takeaways

• InputStreamReader bridges byte streams to character streams by decoding bytes into characters using a specified charset.

• It provides constructors to utilize the default charset, a named charset, or a specific Charset or CharsetDecoder.

• For optimal performance, wrap InputStreamReader within a BufferedReader.

• Key methods include read() for reading characters, close() for releasing resources, and getEncoding() for retrieving the character encoding name.

• InputStreamReader inherits methods from Reader, Object, Readable, Closeable, and AutoCloseable for stream manipulation and object management.

public class InputStreamReader extends Reader

Known Direct Subclasses FileReader FileReader Convenience class for reading character files.

An InputStreamReader is a bridge from byte streams to character streams: It reads bytes and decodes them into characters using a specified charset. The charset that it uses may be specified by name or may be given explicitly, or the platform's default charset may be accepted.

Each invocation of one of an InputStreamReader's read() methods may cause one or more bytes to be read from the underlying byte-input stream. To enable the efficient conversion of bytes to characters, more bytes may be read ahead from the underlying stream than are necessary to satisfy the current read operation.

For top efficiency, consider wrapping an InputStreamReader within a BufferedReader. For example:

 BufferedReader in
   = new BufferedReader(new InputStreamReader(System.in));
 

See Also

• BufferedReader
• InputStream
• Charset

Inherited Field Summary

From class java.io.Reader

protected Object

lock

The object used to synchronize operations on this stream.

Public Constructor Summary

	InputStreamReader(InputStream in) Creates an InputStreamReader that uses the default charset.
	InputStreamReader(InputStream in, String charsetName) Creates an InputStreamReader that uses the named charset.
	InputStreamReader(InputStream in, Charset cs) Creates an InputStreamReader that uses the given charset.
	InputStreamReader(InputStream in, CharsetDecoder dec) Creates an InputStreamReader that uses the given charset decoder.

Public Method Summary

void	close() Closes the stream and releases any system resources associated with it.
String	getEncoding() Returns the name of the character encoding being used by this stream.
int	read() Reads a single character.
int	read(char[] cbuf, int offset, int length) Reads characters into a portion of an array.
boolean	ready() Tells whether this stream is ready to be read.

Inherited Method Summary

From class java.io.Reader

abstract void	close() Closes the stream and releases any system resources associated with it.
void	mark(int readAheadLimit) Marks the present position in the stream.
boolean	markSupported() Tells whether this stream supports the mark() operation.
int	read() Reads a single character.
abstract int	read(char[] cbuf, int off, int len) Reads characters into a portion of an array.
int	read(char[] cbuf) Reads characters into an array.
int	read(CharBuffer target) Attempts to read characters into the specified character buffer.
boolean	ready() Tells whether this stream is ready to be read.
void	reset() Resets the stream.
long	skip(long n) Skips characters.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.lang.Readable

abstract int

read(CharBuffer cb) Attempts to read characters into the specified character buffer.

From interface java.io.Closeable

abstract void

close() Closes this stream and releases any system resources associated with it.

From interface java.lang.AutoCloseable

abstract void

close() Closes this resource, relinquishing any underlying resources.

Public Constructors

public InputStreamReader (InputStream in)

Creates an InputStreamReader that uses the default charset.

Parameters

in	An InputStream

public InputStreamReader (InputStream in, String charsetName)

Creates an InputStreamReader that uses the named charset.

Parameters

in	An InputStream
charsetName	The name of a supported charset

Throws

UnsupportedEncodingException	If the named charset is not supported

public InputStreamReader (InputStream in, Charset cs)

Creates an InputStreamReader that uses the given charset.

Parameters

in	An InputStream
cs	A charset

public InputStreamReader (InputStream in, CharsetDecoder dec)

Creates an InputStreamReader that uses the given charset decoder.

Parameters

in	An InputStream
dec	A charset decoder

Public Methods

public void close ()

Closes the stream and releases any system resources associated with it. Once the stream has been closed, further read(), ready(), mark(), reset(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.

Throws

IOException

public String getEncoding ()

Returns the name of the character encoding being used by this stream.

If the encoding has an historical name then that name is returned; otherwise the encoding's canonical name is returned.

If this instance was created with the InputStreamReader(InputStream, String) constructor then the returned name, being unique for the encoding, may differ from the name passed to the constructor. This method will return null if the stream has been closed.

Returns

• The historical name of this encoding, or null if the stream has been closed

See Also

• Charset

public int read ()

Reads a single character.

Returns

• The character read, or -1 if the end of the stream has been reached

Throws

IOException	If an I/O error occurs

public int read (char[] cbuf, int offset, int length)

Reads characters into a portion of an array.

Parameters

cbuf	Destination buffer
offset	Offset at which to start storing characters
length	Maximum number of characters to read

Returns

• The number of characters read, or -1 if the end of the stream has been reached

Throws

IOException	If an I/O error occurs

public boolean ready ()

Tells whether this stream is ready to be read. An InputStreamReader is ready if its input buffer is not empty, or if bytes are available to be read from the underlying byte stream.

Returns

• True if the next read() is guaranteed not to block for input, false otherwise. Note that returning false does not guarantee that the next read will block.

Throws

IOException	If an I/O error occurs