src/java.base/share/classes/java/io/Writer.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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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.
 *
 * @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
     */
    private char[] writeBuffer;

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

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

    /**
     * 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.
     *
     * @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.
     *
     * <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.
     *
     * @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.
     *
     * @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.
     *
     * @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.
     *
     * @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.
     *
     * <p> An invocation of this method of the form {@code out.append(csq)}
     * when {@code csq} is not {@code null}, behaves in exactly the same way
     * as the invocation
     *
     * {@snippet lang=java :
     *     out.write(csq.toString())
     * }
     *
     * <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.
     *
     * <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
     *
     * {@snippet lang=java :
     *     out.write(csq.subSequence(start, end).toString())
     * }
     *
     * @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.
     *
     * <p> An invocation of this method of the form {@code out.append(c)}
     * behaves in exactly the same way as the invocation
     *
     * {@snippet lang=java :
     *     out.write(c)
     * }
     *
     * @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.
     *
     * <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
     */
    public abstract void close() throws IOException;

}