422 lines
13 KiB
Java
422 lines
13 KiB
Java
/*
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* Copyright (c) 1996, 2011, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.io;
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import java.util.Objects;
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/**
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* Abstract class for writing to character streams. The only methods that a
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* subclass must implement are write(char[], int, int), flush(), and close().
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* Most subclasses, however, will override some of the methods defined here in
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* order to provide higher efficiency, additional functionality, or both.
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*
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* @see BufferedWriter
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* @see CharArrayWriter
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* @see FilterWriter
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* @see OutputStreamWriter
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* @see FileWriter
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* @see PipedWriter
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* @see PrintWriter
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* @see StringWriter
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* @see Reader
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*
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* @author Mark Reinhold
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* @since 1.1
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*/
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public abstract class Writer implements Appendable, Closeable, Flushable {
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/**
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* Temporary buffer used to hold writes of strings and single characters
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*/
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private char[] writeBuffer;
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/**
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* Size of writeBuffer, must be >= 1
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*/
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private static final int WRITE_BUFFER_SIZE = 1024;
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/**
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* Returns a new {@code Writer} which discards all characters. The
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* returned stream is initially open. The stream is closed by calling
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* the {@code close()} method. Subsequent calls to {@code close()} have
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* no effect.
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*
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* <p> While the stream is open, the {@code append(char)}, {@code
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* append(CharSequence)}, {@code append(CharSequence, int, int)},
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* {@code flush()}, {@code write(int)}, {@code write(char[])}, and
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* {@code write(char[], int, int)} methods do nothing. After the stream
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* has been closed, these methods all throw {@code IOException}.
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*
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* <p> The {@link #lock object} used to synchronize operations on the
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* returned {@code Writer} is not specified.
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*
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* @return a {@code Writer} which discards all characters
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*
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* @since 11
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*/
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public static Writer nullWriter() {
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return new Writer() {
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private volatile boolean closed;
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private void ensureOpen() throws IOException {
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if (closed) {
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throw new IOException("Stream closed");
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}
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}
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@Override
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public Writer append(char c) throws IOException {
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ensureOpen();
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return this;
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}
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@Override
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public Writer append(CharSequence csq) throws IOException {
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ensureOpen();
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return this;
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}
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@Override
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public Writer append(CharSequence csq, int start, int end) throws IOException {
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ensureOpen();
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if (csq != null) {
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Objects.checkFromToIndex(start, end, csq.length());
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}
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return this;
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}
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@Override
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public void write(int c) throws IOException {
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ensureOpen();
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}
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@Override
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public void write(char[] cbuf, int off, int len) throws IOException {
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Objects.checkFromIndexSize(off, len, cbuf.length);
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ensureOpen();
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}
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@Override
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public void write(String str) throws IOException {
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Objects.requireNonNull(str);
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ensureOpen();
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}
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@Override
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public void write(String str, int off, int len) throws IOException {
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Objects.checkFromIndexSize(off, len, str.length());
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ensureOpen();
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}
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@Override
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public void flush() throws IOException {
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ensureOpen();
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}
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@Override
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public void close() throws IOException {
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closed = true;
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}
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};
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}
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/**
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* The object used to synchronize operations on this stream. For
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* efficiency, a character-stream object may use an object other than
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* itself to protect critical sections. A subclass should therefore use
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* the object in this field rather than {@code this} or a synchronized
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* method.
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*/
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protected Object lock;
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/**
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* Creates a new character-stream writer whose critical sections will
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* synchronize on the writer itself.
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*/
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protected Writer() {
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this.lock = this;
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}
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/**
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* Creates a new character-stream writer whose critical sections will
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* synchronize on the given object.
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*
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* @param lock
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* Object to synchronize on
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*/
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protected Writer(Object lock) {
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if (lock == null) {
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throw new NullPointerException();
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}
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this.lock = lock;
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}
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/**
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* Writes a single character. The character to be written is contained in
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* the 16 low-order bits of the given integer value; the 16 high-order bits
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* are ignored.
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*
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* <p> Subclasses that intend to support efficient single-character output
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* should override this method.
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*
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* @param c
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* int specifying a character to be written
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*
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* @throws IOException
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* If an I/O error occurs
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*/
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public void write(int c) throws IOException {
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synchronized (lock) {
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if (writeBuffer == null){
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writeBuffer = new char[WRITE_BUFFER_SIZE];
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}
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writeBuffer[0] = (char) c;
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write(writeBuffer, 0, 1);
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}
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}
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/**
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* Writes an array of characters.
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*
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* @param cbuf
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* Array of characters to be written
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*
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* @throws IOException
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* If an I/O error occurs
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*/
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public void write(char cbuf[]) throws IOException {
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write(cbuf, 0, cbuf.length);
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}
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/**
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* Writes a portion of an array of characters.
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*
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* @param cbuf
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* Array of characters
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*
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* @param off
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* Offset from which to start writing characters
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*
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* @param len
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* Number of characters to write
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*
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* @throws IndexOutOfBoundsException
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* Implementations should throw this exception
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* if {@code off} is negative, or {@code len} is negative,
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* or {@code off + len} is negative or greater than the length
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* of the given array
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*
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* @throws IOException
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* If an I/O error occurs
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*/
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public abstract void write(char cbuf[], int off, int len) throws IOException;
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/**
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* Writes a string.
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*
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* @param str
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* String to be written
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*
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* @throws IOException
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* If an I/O error occurs
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*/
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public void write(String str) throws IOException {
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write(str, 0, str.length());
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}
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/**
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* Writes a portion of a string.
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*
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* @implSpec
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* The implementation in this class throws an
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* {@code IndexOutOfBoundsException} for the indicated conditions;
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* overriding methods may choose to do otherwise.
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*
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* @param str
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* A String
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*
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* @param off
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* Offset from which to start writing characters
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*
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* @param len
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* Number of characters to write
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*
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* @throws IndexOutOfBoundsException
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* Implementations should throw this exception
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* if {@code off} is negative, or {@code len} is negative,
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* or {@code off + len} is negative or greater than the length
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* of the given string
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*
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* @throws IOException
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* If an I/O error occurs
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*/
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public void write(String str, int off, int len) throws IOException {
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synchronized (lock) {
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char cbuf[];
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if (len <= WRITE_BUFFER_SIZE) {
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if (writeBuffer == null) {
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writeBuffer = new char[WRITE_BUFFER_SIZE];
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}
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cbuf = writeBuffer;
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} else { // Don't permanently allocate very large buffers.
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cbuf = new char[len];
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}
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str.getChars(off, (off + len), cbuf, 0);
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write(cbuf, 0, len);
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}
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}
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/**
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* Appends the specified character sequence to this writer.
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*
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* <p> An invocation of this method of the form {@code out.append(csq)}
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* behaves in exactly the same way as the invocation
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*
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* <pre>
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* out.write(csq.toString()) </pre>
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*
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* <p> Depending on the specification of {@code toString} for the
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* character sequence {@code csq}, the entire sequence may not be
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* appended. For instance, invoking the {@code toString} method of a
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* character buffer will return a subsequence whose content depends upon
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* the buffer's position and limit.
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*
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* @param csq
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* The character sequence to append. If {@code csq} is
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* {@code null}, then the four characters {@code "null"} are
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* appended to this writer.
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*
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* @return This writer
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*
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* @throws IOException
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* If an I/O error occurs
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*
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* @since 1.5
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*/
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public Writer append(CharSequence csq) throws IOException {
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write(String.valueOf(csq));
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return this;
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}
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/**
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* Appends a subsequence of the specified character sequence to this writer.
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* {@code Appendable}.
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*
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* <p> An invocation of this method of the form
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* {@code out.append(csq, start, end)} when {@code csq}
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* is not {@code null} behaves in exactly the
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* same way as the invocation
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*
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* <pre>{@code
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* out.write(csq.subSequence(start, end).toString())
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* }</pre>
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*
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* @param csq
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* The character sequence from which a subsequence will be
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* appended. If {@code csq} is {@code null}, then characters
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* will be appended as if {@code csq} contained the four
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* characters {@code "null"}.
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*
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* @param start
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* The index of the first character in the subsequence
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*
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* @param end
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* The index of the character following the last character in the
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* subsequence
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*
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* @return This writer
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*
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* @throws IndexOutOfBoundsException
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* If {@code start} or {@code end} are negative, {@code start}
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* is greater than {@code end}, or {@code end} is greater than
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* {@code csq.length()}
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*
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* @throws IOException
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* If an I/O error occurs
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*
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* @since 1.5
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*/
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public Writer append(CharSequence csq, int start, int end) throws IOException {
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if (csq == null) csq = "null";
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return append(csq.subSequence(start, end));
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}
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/**
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* Appends the specified character to this writer.
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*
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* <p> An invocation of this method of the form {@code out.append(c)}
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* behaves in exactly the same way as the invocation
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*
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* <pre>
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* out.write(c) </pre>
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*
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* @param c
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* The 16-bit character to append
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*
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* @return This writer
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*
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* @throws IOException
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* If an I/O error occurs
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*
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* @since 1.5
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*/
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public Writer append(char c) throws IOException {
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write(c);
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return this;
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}
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/**
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* Flushes the stream. If the stream has saved any characters from the
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* various write() methods in a buffer, write them immediately to their
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* intended destination. Then, if that destination is another character or
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* byte stream, flush it. Thus one flush() invocation will flush all the
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* buffers in a chain of Writers and OutputStreams.
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*
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* <p> If the intended destination of this stream is an abstraction provided
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* by the underlying operating system, for example a file, then flushing the
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* stream guarantees only that bytes previously written to the stream are
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* passed to the operating system for writing; it does not guarantee that
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* they are actually written to a physical device such as a disk drive.
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*
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* @throws IOException
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* If an I/O error occurs
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*/
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public abstract void flush() throws IOException;
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/**
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* Closes the stream, flushing it first. Once the stream has been closed,
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* further write() or flush() invocations will cause an IOException to be
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* thrown. Closing a previously closed stream has no effect.
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*
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* @throws IOException
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* If an I/O error occurs
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*/
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public abstract void close() throws IOException;
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}
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