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package java.io;


import java.util.Objects;


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.

Author:     Mark Reinhold
See Also:
Since:      1.1
/**
 * 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.
 *
 * @see   BufferedWriter
 * @see   CharArrayWriter
 * @see   FilterWriter
 * @see   OutputStreamWriter
 * @see   FileWriter
 * @see   PipedWriter
 * @see   PrintWriter
 * @see   StringWriter
 * @see Reader
 *
 * @author      Mark Reinhold
 * @since       1.1
 */

public abstract class Writer implements Appendable, Closeable, Flushable {

    
Temporary buffer used to hold writes of strings and single characters

/**
     * Temporary buffer used to hold writes of strings and single characters
     */
    private char[] writeBuffer;

    
Size of writeBuffer, must be >= 1

/**
     * Size of writeBuffer, must be >= 1
     */
    private static final int WRITE_BUFFER_SIZE = 1024;

    
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
/**
     * Returns a new {@code Writer} which discards all characters.  The
     * returned stream is initially open.  The stream is closed by calling
     * the {@code close()} method.  Subsequent calls to {@code close()} have
     * no effect.
     *
     * <p> While the stream is open, the {@code append(char)}, {@code
     * append(CharSequence)}, {@code append(CharSequence, int, int)},
     * {@code flush()}, {@code write(int)}, {@code write(char[])}, and
     * {@code write(char[], int, int)} methods do nothing. After the stream
     * has been closed, these methods all throw {@code IOException}.
     *
     * <p> The {@link #lock object} used to synchronize operations on the
     * returned {@code Writer} is not specified.
     *
     * @return a {@code Writer} which discards all characters
     *
     * @since 11
     */
    public static Writer nullWriter() {
        return new Writer() {
            private volatile boolean closed;

            private void ensureOpen() throws IOException {
                if (closed) {
                    throw new IOException("Stream closed");
                }
            }

            @Override
            public Writer append(char c) throws IOException {
                ensureOpen();
                return this;
            }

            @Override
            public Writer append(CharSequence csq) throws IOException {
                ensureOpen();
                return this;
            }

            @Override
            public Writer append(CharSequence csq, int start, int end) throws IOException {
                ensureOpen();
                if (csq != null) {
                    Objects.checkFromToIndex(start, end, csq.length());
                }
                return this;
            }

            @Override
            public void write(int c) throws IOException {
                ensureOpen();
            }

            @Override
            public void write(char[] cbuf, int off, int len) throws IOException {
                Objects.checkFromIndexSize(off, len, cbuf.length);
                ensureOpen();
            }

            @Override
            public void write(String str) throws IOException {
                Objects.requireNonNull(str);
                ensureOpen();
            }

            @Override
            public void write(String str, int off, int len) throws IOException {
                Objects.checkFromIndexSize(off, len, str.length());
                ensureOpen();
            }

            @Override
            public void flush() throws IOException {
                ensureOpen();
            }

            @Override
            public void close() throws IOException {
                closed = true;
            }
        };
    }

    
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. 
/**
     * 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 {@code this} or a synchronized
     * method.
     */
    protected Object lock;

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

/**
     * Creates a new character-stream writer whose critical sections will
     * synchronize on the writer itself.
     */
    protected Writer() {
        this.lock = this;
    }

    
Creates a new character-stream writer whose critical sections will
synchronize on the given object.

Params:
  • lock – 
        Object to synchronize on
/**
     * Creates a new character-stream writer whose critical sections will
     * synchronize on the given object.
     *
     * @param  lock
     *         Object to synchronize on
     */
    protected Writer(Object lock) {
        if (lock == null) {
            throw new NullPointerException();
        }
        this.lock = lock;
    }

    
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.

Params:
  • c – 
        int specifying a character to be written
Throws:
/**
     * 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.
     *
     * <p> Subclasses that intend to support efficient single-character output
     * should override this method.
     *
     * @param  c
     *         int specifying a character to be written
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public void write(int c) throws IOException {
        synchronized (lock) {
            if (writeBuffer == null){
                writeBuffer = new char[WRITE_BUFFER_SIZE];
            }
            writeBuffer[0] = (char) c;
            write(writeBuffer, 0, 1);
        }
    }

    
Writes an array of characters.

Params:
  • cbuf – 
        Array of characters to be written
Throws:
/**
     * Writes an array of characters.
     *
     * @param  cbuf
     *         Array of characters to be written
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public void write(char cbuf[]) throws IOException {
        write(cbuf, 0, cbuf.length);
    }

    
Writes a portion of an array of characters.

Params:
  • 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
/**
     * Writes a portion of an array of characters.
     *
     * @param  cbuf
     *         Array of characters
     *
     * @param  off
     *         Offset from which to start writing characters
     *
     * @param  len
     *         Number of characters to write
     *
     * @throws  IndexOutOfBoundsException
     *          Implementations should throw this exception
     *          if {@code off} is negative, or {@code len} is negative,
     *          or {@code off + len} is negative or greater than the length
     *          of the given array
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public abstract void write(char cbuf[], int off, int len) throws IOException;

    
Writes a string.

Params:
  • str – 
        String to be written
Throws:
/**
     * Writes a string.
     *
     * @param  str
     *         String to be written
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public void write(String str) throws IOException {
        write(str, 0, str.length());
    }

    
Writes a portion of a string.

Params:
  • 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
Implementation Requirements: The implementation in this class throws an IndexOutOfBoundsException for the indicated conditions; overriding methods may choose to do otherwise.
/**
     * Writes a portion of a string.
     *
     * @implSpec
     * The implementation in this class throws an
     * {@code IndexOutOfBoundsException} for the indicated conditions;
     * overriding methods may choose to do otherwise.
     *
     * @param  str
     *         A String
     *
     * @param  off
     *         Offset from which to start writing characters
     *
     * @param  len
     *         Number of characters to write
     *
     * @throws  IndexOutOfBoundsException
     *          Implementations should throw this exception
     *          if {@code off} is negative, or {@code len} is negative,
     *          or {@code off + len} is negative or greater than the length
     *          of the given string
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public void write(String str, int off, int len) throws IOException {
        synchronized (lock) {
            char cbuf[];
            if (len <= WRITE_BUFFER_SIZE) {
                if (writeBuffer == null) {
                    writeBuffer = new char[WRITE_BUFFER_SIZE];
                }
                cbuf = writeBuffer;
            } else {    // Don't permanently allocate very large buffers.
                cbuf = new char[len];
            }
            str.getChars(off, (off + len), cbuf, 0);
            write(cbuf, 0, len);
        }
    }

    
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. 
Params:
  • csq –  The character sequence to append. If csq is null, then the four characters "null" are appended to this writer.
Throws:
Returns: This writer
Since: 1.5
/**
     * Appends the specified character sequence to this writer.
     *
     * <p> An invocation of this method of the form {@code out.append(csq)}
     * behaves in exactly the same way as the invocation
     *
     * <pre>
     *     out.write(csq.toString()) </pre>
     *
     * <p> Depending on the specification of {@code toString} for the
     * character sequence {@code csq}, the entire sequence may not be
     * appended. For instance, invoking the {@code toString} method of a
     * character buffer will return a subsequence whose content depends upon
     * the buffer's position and limit.
     *
     * @param  csq
     *         The character sequence to append.  If {@code csq} is
     *         {@code null}, then the four characters {@code "null"} are
     *         appended to this writer.
     *
     * @return  This writer
     *
     * @throws  IOException
     *          If an I/O error occurs
     *
     * @since  1.5
     */
    public Writer append(CharSequence csq) throws IOException {
        write(String.valueOf(csq));
        return this;
    }

    
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())



Params:
  • 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
Throws:
Returns: This writer
Since: 1.5
/**
     * Appends a subsequence of the specified character sequence to this writer.
     * {@code Appendable}.
     *
     * <p> An invocation of this method of the form
     * {@code out.append(csq, start, end)} when {@code csq}
     * is not {@code null} behaves in exactly the
     * same way as the invocation
     *
     * <pre>{@code
     *     out.write(csq.subSequence(start, end).toString())
     * }</pre>
     *
     * @param  csq
     *         The character sequence from which a subsequence will be
     *         appended.  If {@code csq} is {@code null}, then characters
     *         will be appended as if {@code csq} contained the four
     *         characters {@code "null"}.
     *
     * @param  start
     *         The index of the first character in the subsequence
     *
     * @param  end
     *         The index of the character following the last character in the
     *         subsequence
     *
     * @return  This writer
     *
     * @throws  IndexOutOfBoundsException
     *          If {@code start} or {@code end} are negative, {@code start}
     *          is greater than {@code end}, or {@code end} is greater than
     *          {@code csq.length()}
     *
     * @throws  IOException
     *          If an I/O error occurs
     *
     * @since  1.5
     */
    public Writer append(CharSequence csq, int start, int end) throws IOException {
        if (csq == null) csq = "null";
        return append(csq.subSequence(start, end));
    }

    
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) 


Params:
  • c – 
        The 16-bit character to append
Throws:
Returns: This writer
Since:1.5
/**
     * Appends the specified character to this writer.
     *
     * <p> An invocation of this method of the form {@code out.append(c)}
     * behaves in exactly the same way as the invocation
     *
     * <pre>
     *     out.write(c) </pre>
     *
     * @param  c
     *         The 16-bit character to append
     *
     * @return  This writer
     *
     * @throws  IOException
     *          If an I/O error occurs
     *
     * @since 1.5
     */
    public Writer append(char c) throws IOException {
        write(c);
        return this;
    }

    
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.

Throws:
  • IOException – 
         If an I/O error occurs
/**
     * 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.
     *
     * <p> 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.
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public abstract void flush() 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.

Throws:
  • IOException – 
         If an I/O error occurs
/**
     * 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.
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public abstract void close() throws IOException;

}