/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package java.io;
/**
* The base class for all writers. A writer is a means of writing data to a
* target in a character-wise manner. Most output streams expect the
* {@link #flush()} method to be called before closing the stream, to ensure all
* data is actually written out.
* <p>
* This abstract class does not provide a fully working implementation, so it
* needs to be subclassed, and at least the {@link #write(char[], int, int)},
* {@link #close()} and {@link #flush()} methods needs to be overridden.
* Overriding some of the non-abstract methods is also often advised, since it
* might result in higher efficiency.
* <p>
* Many specialized readers for purposes like reading from a file already exist
* in this package.
*
* @see Reader
*/
public abstract class Writer implements Appendable, Closeable, Flushable {
/**
* The object used to synchronize access to the writer.
*/
protected Object lock;
/**
* Constructs a new {@code Writer} with {@code this} as the object used to
* synchronize critical sections.
*/
protected Writer() {
lock = this;
}
/**
* Constructs a new {@code Writer} with {@code lock} used to synchronize
* critical sections.
*
* @param lock
* the {@code Object} used to synchronize critical sections.
* @throws NullPointerException
* if {@code lock} is {@code null}.
*/
protected Writer(Object lock) {
if (lock == null) {
throw new NullPointerException("lock == null");
}
this.lock = lock;
}
/**
* Closes this writer. Implementations of this method should free any
* resources associated with the writer.
*
* @throws IOException
* if an error occurs while closing this writer.
*/
public abstract void close() throws IOException;
/**
* Flushes this writer. Implementations of this method should ensure that
* all buffered characters are written to the target.
*
* @throws IOException
* if an error occurs while flushing this writer.
*/
public abstract void flush() throws IOException;
/**
* Writes the entire character buffer {@code buf} to the target.
*
* @param buf
* the non-null array containing characters to write.
* @throws IOException
* if this writer is closed or another I/O error occurs.
*/
public void write(char[] buf) throws IOException {
write(buf, 0, buf.length);
}
/**
* Writes {@code count} characters starting at {@code offset} in {@code buf}
* to the target.
*
* @param buf
* the non-null character array to write.
* @param offset
* the index of the first character in {@code buf} to write.
* @param count
* the maximum number of characters to write.
* @throws IndexOutOfBoundsException
* if {@code offset < 0} or {@code count < 0}, or if {@code
* offset + count} is greater than the size of {@code buf}.
* @throws IOException
* if this writer is closed or another I/O error occurs.
*/
public abstract void write(char[] buf, int offset, int count) throws IOException;
/**
* Writes one character to the target. Only the two least significant bytes
* of the integer {@code oneChar} are written.
*
* @param oneChar
* the character to write to the target.
* @throws IOException
* if this writer is closed or another I/O error occurs.
*/
public void write(int oneChar) throws IOException {
synchronized (lock) {
char[] oneCharArray = new char[1];
oneCharArray[0] = (char) oneChar;
write(oneCharArray);
}
}
/**
* Writes the characters from the specified string to the target.
*
* @param str
* the non-null string containing the characters to write.
* @throws IOException
* if this writer is closed or another I/O error occurs.
*/
public void write(String str) throws IOException {
write(str, 0, str.length());
}
/**
* Writes {@code count} characters from {@code str} starting at {@code
* offset} to the target.
*
* @param str
* the non-null string containing the characters to write.
* @param offset
* the index of the first character in {@code str} to write.
* @param count
* the number of characters from {@code str} to write.
* @throws IOException
* if this writer is closed or another I/O error occurs.
* @throws IndexOutOfBoundsException
* if {@code offset < 0} or {@code count < 0}, or if {@code
* offset + count} is greater than the length of {@code str}.
*/
public void write(String str, int offset, int count) throws IOException {
if ((offset | count) < 0 || offset > str.length() - count) {
throw new StringIndexOutOfBoundsException(str, offset, count);
}
char[] buf = new char[count];
str.getChars(offset, offset + count, buf, 0);
synchronized (lock) {
write(buf, 0, buf.length);
}
}
/**
* Appends the character {@code c} to the target. This method works the same
* way as {@link #write(int)}.
*
* @param c
* the character to append to the target stream.
* @return this writer.
* @throws IOException
* if this writer is closed or another I/O error occurs.
*/
public Writer append(char c) throws IOException {
write(c);
return this;
}
/**
* Appends the character sequence {@code csq} to the target. This method
* works the same way as {@code Writer.write(csq.toString())}. If {@code
* csq} is {@code null}, then the string "null" is written to the target
* stream.
*
* @param csq
* the character sequence appended to the target.
* @return this writer.
* @throws IOException
* if this writer is closed or another I/O error occurs.
*/
public Writer append(CharSequence csq) throws IOException {
if (csq == null) {
csq = "null";
}
write(csq.toString());
return this;
}
/**
* Appends a subsequence of the character sequence {@code csq} to the
* target. This method works the same way as {@code
* Writer.writer(csq.subsequence(start, end).toString())}. If {@code
* csq} is {@code null}, then the specified subsequence of the string "null"
* will be written to the target.
*
* @param csq
* the character sequence appended to the target.
* @param start
* the index of the first char in the character sequence appended
* to the target.
* @param end
* the index of the character following the last character of the
* subsequence appended to the target.
* @return this writer.
* @throws IOException
* if this writer is closed or another I/O error occurs.
* @throws IndexOutOfBoundsException
* if {@code start > end}, {@code start < 0}, {@code end < 0} or
* either {@code start} or {@code end} are greater or equal than
* the length of {@code csq}.
*/
public Writer append(CharSequence csq, int start, int end) throws IOException {
if (csq == null) {
csq = "null";
}
write(csq.subSequence(start, end).toString());
return this;
}
/**
* Returns true if this writer has encountered and suppressed an error. Used
* by PrintWriters as an alternative to checked exceptions.
*/
boolean checkError() {
return false;
}
}