[Chapter 11] Writer

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| Chapter 11 The java.io Package |

# Writer

## Name

Writer

## Synopsis

Class Name:

  `java.io.Writer`

Superclass:

  `java.lang.Object`

Immediate Subclasses:

  `java.io.BufferedWriter`, `java.io.CharArrayWriter`,

  `java.io.FilterWriter`, `java.io.OutputStreamWriter`,

  `java.io.PipedWriter`, `java.io.PrintWriter`,

  `java.io.StringWriter`

Interfaces Implemented:

  None

Availability:

  New as of JDK 1.1

## Description

The `Writer` class is an `abstract` class that is the superclass of all classes that represent output character streams. `Writer` defines the basic output methods that all character streams provide. A similar hierarchy of classes, based around `OutputStream`, deals with byte streams instead of character streams.

`Writer` is designed so that `write(int` `b)` and `write(char[])` both call `write(char[],` `int,` `int)`. Thus, a subclass can simply override `write(char[],` `int,` `int)` and all of the `write` methods will work. Note that this is different from the design of `OutputStream`, where the `write(int` `b)` method is the catch-all method. The design of `Writer` is cleaner and more efficient.

Some `Writer` subclasses may implement buffering to increase efficiency. `Writer` provides a method--`flush()`--that tells the `Writer` to write any buffered output to the underlying device, which may be a disk drive or a network.

## Class Summary

    public abstract class java.io.Writer extends java.lang.Object {
      // Variables
      protected Object lock;
      // Constructors
      protected Writer();
      protected Writer(Object lock);
      // Instance Methods
      public abstract void close();
      public abstract void flush();
      public void write(int c);
      public void write(char[] cbuf);
      public abstract void write(char[] cbuf, int off, int len);
      public void write(String str);
      public void write(String str, int off, int len);
    }

## Variables

### lock

#### protected Object lock

Description

  The object used to synchronize operations on this `Writer` object. For efficiency's sake, a particular implementation of a character stream can choose to synchronize its operations on something other than instances of itself. Thus, any subclass should synchronize on the `lock` object, instead of using a `synchronized` method or the `this` object.

## Constructors

### Writer

#### protected Writer()

Description

  This constructor creates a `Writer` that synchronizes on the `Writer` itself, or in other words, on the `this` object.

#### protected Writer(Object lock)

Parameters

  `lock`

    The object to use for synchronization.

Description

  This constructor creates a `Writer` that synchronizes on the given object.

## Instance Methods

### close

#### public abstract void close() throws IOException

Throws

  `IOException`

    If any kind of I/O error occurs.

Description

  This method flushes the writer and then closes it, releasing any system resources associated with it.

  A subclass of `Writer` must implement this method.

### flush

#### public void flush() throws IOException

Throws

  `IOException`

    If any kind of I/O error occurs.

Description

  This method forces any characters that may be buffered by this `Writer` to be written to the underlying device.

  A subclass of `Writer` must implement this method.

### write

#### public void write(int c) throws IOException

Parameters

  `c`

    The value to write.

Throws

  `IOException`

    If any kind of I/O error occurs.

Description

  This method writes a character containing the lowest sixteen bits of the given integer value.

  The implementation of this method in `Writer` writes the character by calling `write(cb,` `1)` where `cb` is a character array that contains the given value in `cb[0]`. Although it is not strictly necessary, a subclass that wants to provide efficient single-character writes should override this method.

#### public void write(char[] cbuf) throws IOException

Parameters

  `cbuf`

    An array of characters to write to the stream.

Throws

  `IOException`

    If any kind of I/O error occurs.

Description

  This method writes the given array of characters to the stream by calling `write(cbuf,` `0,` `cbuf.length)`.

  A subclass does not usually need to override this method, as it can override `write(char[],` `int,` `int)` and have `write(char[])` work automatically.

####

     public abstract void write(char[] cbuf, int off, int len) throws IOException

Parameters

  `cbuf`

    An array of characters to write to the stream.

  `off`

    An offset into the array.

  `len`

    The number of characters to write.

Throws

  `IOException`

    If any kind of I/O error occurs.

Description

  This method writes `len` characters contained in the given array starting at index `off`.

  A subclass of `Writer` must implement this method.

#### public void write(String str) throws IOException

Parameters

  `str`

    A string to write to the stream.

Throws

  `IOException`

    If any kind of I/O error occurs.

Description

  This method writes the given string to the stream by calling `write(str,str.length)`.

  A subclass does not usually need to override this method, as it can override `write(char[],` `int,` `int)` and have it work automatically.

#### public void write(String str, int off, int len) throws IOException

Parameters

  `str`

    A string to write to the stream.

  `off`

    An offset into the string.

  `len`

    The number of characters to write.

Throws

  `IOException`

    If any kind of I/O error occurs.

Description

  This method writes `len` characters contained in the given string starting at index `off`. The method does this by creating an array of characters for the specified portion of the string and then calling `write(cb, 0, cb.length)` on the character array `cb`.

  A subclass does not usually need to override this method, as it can override `write(char[],` `int,` `int)` and have it work automatically.

## Inherited Methods

Method | Inherited From | Method | Inherited From
--- | --- | --- | ---
`clone()` | `Object` | `equals(Object)` | `Object`
`finalize()` | `Object` | `getClass()` | `Object`
`hashCode()` | `Object` | `notify()` | `Object`
`notifyAll()` | `Object` | `toString()` | `Object`
`wait()` | `Object` | `wait(long)` | `Object`
`wait(long, int)` | `Object` |  |

## See Also

`BufferedWriter`, `CharArrayWriter`, `FilterWriter`, `IOException`, `OutputStreamWriter`, `PipedWriter`, `PrintWriter`, `StringWriter`

WriteAbortedException |  | AbstractMethodError