Module java.base
Package java.io

# Class Writer

java.lang.Object
java.io.Writer

All Implemented Interfaces:
  `Closeable`, `Flushable`, `Appendable`, `AutoCloseable`

Direct Known Subclasses:
  `BufferedWriter`, `CharArrayWriter`, `FilterWriter`, `OutputStreamWriter`, `PipedWriter`, `PrintWriter`, `StringWriter`

public abstract class Writer extends Object implements Appendable, Closeable, Flushable
Abstract class for writing to character streams. The only methods that a subclass must implement are write(char[], int, int), flush(), and close(). Most subclasses, however, will override some of the methods defined here in order to provide higher efficiency, additional functionality, or both.

Since:
  1.1
See Also:
  - `BufferedWriter`
  - `CharArrayWriter`
  - `FilterWriter`
  - `OutputStreamWriter`
  - `FileWriter`
  - `PipedWriter`
  - `PrintWriter`
  - `StringWriter`
  - `Reader`

## Field Summary

Fields
Modifier and Type
Field
Description
`protected Object`
`lock`
The object used to synchronize operations on this stream.

## Constructor Summary

Constructors
Modifier
Constructor
Description
`protected`
`Writer()`
Creates a new character-stream writer whose critical sections will synchronize on the writer itself.
`protected`
`Writer(Object lock)`
Creates a new character-stream writer whose critical sections will synchronize on the given object.

## Method Summary

Modifier and Type
Method
Description
`Writer`
`append(char c)`
Appends the specified character to this writer.
`Writer`
`append(CharSequence csq)`
Appends the specified character sequence to this writer.
`Writer`
`append(CharSequence csq, int start, int end)`
Appends a subsequence of the specified character sequence to this writer.
`abstract void`
`close()`
Closes the stream, flushing it first.
`abstract void`
`flush()`
Flushes the stream.
`static Writer`
`nullWriter()`
Returns a new `Writer` which discards all characters.
`void`
`write(char[] cbuf)`
Writes an array of characters.
`abstract void`
`write(char[] cbuf, int off, int len)`
Writes a portion of an array of characters.
`void`
`write(int c)`
Writes a single character.
`void`
`write(String str)`
Writes a string.
`void`
`write(String str, int off, int len)`
Writes a portion of a string.

### Methods declared in class java.lang.Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

## Field Details

### lock

protected Object lock
The object used to synchronize operations on this stream. For efficiency, a character-stream object may use an object other than itself to protect critical sections. A subclass should therefore use the object in this field rather than `this` or a synchronized method.

## Constructor Details

### Writer

protected Writer()
Creates a new character-stream writer whose critical sections will synchronize on the writer itself.

### Writer

protected Writer(Object lock)
Creates a new character-stream writer whose critical sections will synchronize on the given object.

Parameters:
  `lock` - Object to synchronize on

## Method Details

### nullWriter

public static Writer nullWriter()
Returns a new `Writer` which discards all characters. The returned stream is initially open. The stream is closed by calling the `close()` method. Subsequent calls to `close()` have no effect.

While the stream is open, the `append(char)`, `append(CharSequence)`, `append(CharSequence, int, int)`, `flush()`, `write(int)`, `write(char[])`, and `write(char[], int, int)` methods do nothing. After the stream has been closed, these methods all throw `IOException`.

The `object` used to synchronize operations on the returned `Writer` is not specified.

Returns:
  a `Writer` which discards all characters
Since:
  11

### write

public void write(int c) throws IOException
Writes a single character. The character to be written is contained in the 16 low-order bits of the given integer value; the 16 high-order bits are ignored.

Subclasses that intend to support efficient single-character output should override this method.

Parameters:
  `c` - int specifying a character to be written
Throws:
  `IOException` - If an I/O error occurs

### write

public void write(char[] cbuf) throws IOException
Writes an array of characters.

Parameters:
  `cbuf` - Array of characters to be written
Throws:
  `IOException` - If an I/O error occurs

### write

public abstract void write(char[] cbuf, int off, int len) throws IOException
Writes a portion of an array of characters.

Parameters:
  `cbuf` - Array of characters
  `off` - Offset from which to start writing characters
  `len` - Number of characters to write
Throws:
  `IndexOutOfBoundsException` - Implementations should throw this exception if `off` is negative, or `len` is negative, or `off + len` is negative or greater than the length of the given array
  `IOException` - If an I/O error occurs

### write

public void write(String str) throws IOException
Writes a string.

Parameters:
  `str` - String to be written
Throws:
  `IOException` - If an I/O error occurs

### write

public void write(String str, int off, int len) throws IOException
Writes a portion of a string.

Implementation Requirements:
  The implementation in this class throws an `IndexOutOfBoundsException` for the indicated conditions; overriding methods may choose to do otherwise.
Parameters:
  `str` - A String
  `off` - Offset from which to start writing characters
  `len` - Number of characters to write
Throws:
  `IndexOutOfBoundsException` - Implementations should throw this exception if `off` is negative, or `len` is negative, or `off + len` is negative or greater than the length of the given string
  `IOException` - If an I/O error occurs

### append

public Writer append(CharSequence csq) throws IOException
Appends the specified character sequence to this writer.

An invocation of this method of the form `out.append(csq)` behaves in exactly the same way as the invocation

        out.write(csq.toString())

Depending on the specification of `toString` for the character sequence `csq`, the entire sequence may not be appended. For instance, invoking the `toString` method of a character buffer will return a subsequence whose content depends upon the buffer's position and limit.

Specified by:
  `append` in interface `Appendable`
Parameters:
  `csq` - The character sequence to append. If `csq` is `null`, then the four characters `"null"` are appended to this writer.
Returns:
  This writer
Throws:
  `IOException` - If an I/O error occurs
Since:
  1.5

### append

public Writer append(CharSequence csq, int start, int end) throws IOException
Appends a subsequence of the specified character sequence to this writer. `Appendable`.

An invocation of this method of the form `out.append(csq, start, end)` when `csq` is not `null` behaves in exactly the same way as the invocation

        out.write(csq.subSequence(start, end).toString())

Specified by:
  `append` in interface `Appendable`
Parameters:
  `csq` - The character sequence from which a subsequence will be appended. If `csq` is `null`, then characters will be appended as if `csq` contained the four characters `"null"`.
  `start` - The index of the first character in the subsequence
  `end` - The index of the character following the last character in the subsequence
Returns:
  This writer
Throws:
  `IndexOutOfBoundsException` - If `start` or `end` are negative, `start` is greater than `end`, or `end` is greater than `csq.length()`
  `IOException` - If an I/O error occurs
Since:
  1.5

### append

public Writer append(char c) throws IOException
Appends the specified character to this writer.

An invocation of this method of the form `out.append(c)` behaves in exactly the same way as the invocation

        out.write(c)

Specified by:
  `append` in interface `Appendable`
Parameters:
  `c` - The 16-bit character to append
Returns:
  This writer
Throws:
  `IOException` - If an I/O error occurs
Since:
  1.5

### flush

public abstract void flush() throws IOException
Flushes the stream. If the stream has saved any characters from the various write() methods in a buffer, write them immediately to their intended destination. Then, if that destination is another character or byte stream, flush it. Thus one flush() invocation will flush all the buffers in a chain of Writers and OutputStreams.

If the intended destination of this stream is an abstraction provided by the underlying operating system, for example a file, then flushing the stream guarantees only that bytes previously written to the stream are passed to the operating system for writing; it does not guarantee that they are actually written to a physical device such as a disk drive.

Specified by:
  `flush` in interface `Flushable`
Throws:
  `IOException` - If an I/O error occurs

### close

public abstract void close() throws IOException
Closes the stream, flushing it first. Once the stream has been closed, further write() or flush() invocations will cause an IOException to be thrown. Closing a previously closed stream has no effect.

Specified by:
  `close` in interface `AutoCloseable`
Specified by:
  `close` in interface `Closeable`
Throws:
  `IOException` - If an I/O error occurs