StringWriter (Java Platform SE 8 )
Keywords: java.io.StringWriter class
Date: 2026-04-17

compact1, compact2, compact3
java.io

## Class StringWriter

- java.lang.Object
- - java.io.Writer
  - - java.io.StringWriter

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

      public class StringWriter
      extends Writer

  A character stream that collects its output in a string buffer, which can then be used to construct a string.

  Closing a `StringWriter` has no effect. The methods in this class can be called after the stream has been closed without generating an `IOException`.

  Since:
    JDK1.1

- - ### Field Summary

    - ### Fields inherited from class java.io.Writer

      `lock`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `StringWriter()` Create a new string writer using the default initial string-buffer size.
    `StringWriter(int initialSize)` Create a new string writer using the specified initial string-buffer size.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `StringWriter` | `append(char c)` Appends the specified character to this writer.
    `StringWriter` | `append(CharSequence csq)` Appends the specified character sequence to this writer.
    `StringWriter` | `append(CharSequence csq, int start, int end)` Appends a subsequence of the specified character sequence to this writer.
    `void` | `close()` Closing a `StringWriter` has no effect.
    `void` | `flush()` Flush the stream.
    `StringBuffer` | `getBuffer()` Return the string buffer itself.
    `String` | `toString()` Return the buffer's current value as a string.
    `void` | `write(char[] cbuf, int off, int len)` Write a portion of an array of characters.
    `void` | `write(int c)` Write a single character.
    `void` | `write(String str)` Write a string.
    `void` | `write(String str, int off, int len)` Write a portion of a string.

    - ### Methods inherited from class java.io.Writer

      `write`

    - ### Methods inherited from class java.lang.Object

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

- - ### Constructor Detail

    - #### StringWriter

          public StringWriter()

      Create a new string writer using the default initial string-buffer size.

    - #### StringWriter

          public StringWriter(int initialSize)

      Create a new string writer using the specified initial string-buffer size.
      Parameters:
        `initialSize` - The number of `char` values that will fit into this buffer before it is automatically expanded
      Throws:
        `IllegalArgumentException` - If `initialSize` is negative

  - ### Method Detail

    - #### write

          public void write(int c)

      Write a single character.
      Overrides:
        `write` in class `Writer`
      Parameters:
        `c` - int specifying a character to be written

    - #### write

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

      Write a portion of an array of characters.
      Specified by:
        `write` in class `Writer`
      Parameters:
        `cbuf` - Array of characters
        `off` - Offset from which to start writing characters
        `len` - Number of characters to write

    - #### write

          public void write(String str)

      Write a string.
      Overrides:
        `write` in class `Writer`
      Parameters:
        `str` - String to be written

    - #### write

          public void write(String str,
                            int off,
                            int len)

      Write a portion of a string.
      Overrides:
        `write` in class `Writer`
      Parameters:
        `str` - String to be written
        `off` - Offset from which to start writing characters
        `len` - Number of characters to write

    - #### append

          public StringWriter append(CharSequence csq)

      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`
      Overrides:
        `append` in class `Writer`
      Parameters:
        `csq` - The character sequence to append. If `csq` is `null`, then the four characters `"null"` are appended to this writer.
      Returns:
        This writer
      Since:
        1.5

    - #### append

          public StringWriter append(CharSequence csq,
                                     int start,
                                     int end)

      Appends a subsequence of the specified character sequence to this writer.

      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`
      Overrides:
        `append` in class `Writer`
      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()`
      Since:
        1.5

    - #### append

          public StringWriter append(char c)

      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`
      Overrides:
        `append` in class `Writer`
      Parameters:
        `c` - The 16-bit character to append
      Returns:
        This writer
      Since:
        1.5

    - #### toString

          public String toString()

      Return the buffer's current value as a string.
      Overrides:
        `toString` in class `Object`
      Returns:
        a string representation of the object.

    - #### getBuffer

          public StringBuffer getBuffer()

      Return the string buffer itself.
      Returns:
        StringBuffer holding the current buffer value.

    - #### flush

          public void flush()

      Flush the stream.
      Specified by:
        `flush` in interface `Flushable`
      Specified by:
        `flush` in class `Writer`

    - #### close

          public void close()
                     throws IOException

      Closing a `StringWriter` has no effect. The methods in this class can be called after the stream has been closed without generating an `IOException`.
      Specified by:
        `close` in interface `Closeable`
      Specified by:
        `close` in interface `AutoCloseable`
      Specified by:
        `close` in class `Writer`
      Throws:
        `IOException` - If an I/O error occurs

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