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package java.io;
A character stream whose source is a string.
Author: Mark Reinhold Since: 1.1
/**
* A character stream whose source is a string.
*
* @author Mark Reinhold
* @since 1.1
*/
public class StringReader extends Reader {
private String str;
private int length;
private int next = 0;
private int mark = 0;
Creates a new string reader.
Params: - s – String providing the character stream.
/**
* Creates a new string reader.
*
* @param s String providing the character stream.
*/
public StringReader(String s) {
this.str = s;
this.length = s.length();
}
Check to make sure that the stream has not been closed /** Check to make sure that the stream has not been closed */
private void ensureOpen() throws IOException {
if (str == null)
throw new IOException("Stream closed");
}
Reads a single character.
Throws: - IOException – If an I/O error occurs
Returns: The character read, or -1 if the end of the stream has been
reached
/**
* Reads a single character.
*
* @return The character read, or -1 if the end of the stream has been
* reached
*
* @exception IOException If an I/O error occurs
*/
public int read() throws IOException {
synchronized (lock) {
ensureOpen();
if (next >= length)
return -1;
return str.charAt(next++);
}
}
Reads characters into a portion of an array.
Params: - cbuf – Destination buffer
- off – Offset at which to start writing characters
- len – Maximum number of characters to read
Throws: - IOException – If an I/O error occurs
- IndexOutOfBoundsException – {@inheritDoc}
Returns: The number of characters read, or -1 if the end of the
stream has been reached
/**
* Reads characters into a portion of an array.
*
* @param cbuf Destination buffer
* @param off Offset at which to start writing characters
* @param len Maximum number of characters to read
*
* @return The number of characters read, or -1 if the end of the
* stream has been reached
*
* @exception IOException If an I/O error occurs
* @exception IndexOutOfBoundsException {@inheritDoc}
*/
public int read(char cbuf[], int off, int len) throws IOException {
synchronized (lock) {
ensureOpen();
if ((off < 0) || (off > cbuf.length) || (len < 0) ||
((off + len) > cbuf.length) || ((off + len) < 0)) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
}
if (next >= length)
return -1;
int n = Math.min(length - next, len);
str.getChars(next, next + n, cbuf, off);
next += n;
return n;
}
}
Skips the specified number of characters in the stream. Returns
the number of characters that were skipped.
The ns parameter may be negative, even though the
skip method of the Reader superclass throws an exception in this case. Negative values of ns cause the
stream to skip backwards. Negative return values indicate a skip
backwards. It is not possible to skip backwards past the beginning of
the string.
If the entire string has been read or skipped, then this method has
no effect and always returns 0.
Throws: - IOException – If an I/O error occurs
/**
* Skips the specified number of characters in the stream. Returns
* the number of characters that were skipped.
*
* <p>The <code>ns</code> parameter may be negative, even though the
* <code>skip</code> method of the {@link Reader} superclass throws
* an exception in this case. Negative values of <code>ns</code> cause the
* stream to skip backwards. Negative return values indicate a skip
* backwards. It is not possible to skip backwards past the beginning of
* the string.
*
* <p>If the entire string has been read or skipped, then this method has
* no effect and always returns 0.
*
* @exception IOException If an I/O error occurs
*/
public long skip(long ns) throws IOException {
synchronized (lock) {
ensureOpen();
if (next >= length)
return 0;
// Bound skip by beginning and end of the source
long n = Math.min(length - next, ns);
n = Math.max(-next, n);
next += n;
return n;
}
}
Tells whether this stream is ready to be read.
Throws: - IOException – If the stream is closed
Returns: True if the next read() is guaranteed not to block for input
/**
* Tells whether this stream is ready to be read.
*
* @return True if the next read() is guaranteed not to block for input
*
* @exception IOException If the stream is closed
*/
public boolean ready() throws IOException {
synchronized (lock) {
ensureOpen();
return true;
}
}
Tells whether this stream supports the mark() operation, which it does.
/**
* Tells whether this stream supports the mark() operation, which it does.
*/
public boolean markSupported() {
return true;
}
Marks the present position in the stream. Subsequent calls to reset()
will reposition the stream to this point.
Params: - readAheadLimit – Limit on the number of characters that may be
read while still preserving the mark. Because
the stream's input comes from a string, there
is no actual limit, so this argument must not
be negative, but is otherwise ignored.
Throws: - IllegalArgumentException – If
readAheadLimit < 0 - IOException – If an I/O error occurs
/**
* Marks the present position in the stream. Subsequent calls to reset()
* will reposition the stream to this point.
*
* @param readAheadLimit Limit on the number of characters that may be
* read while still preserving the mark. Because
* the stream's input comes from a string, there
* is no actual limit, so this argument must not
* be negative, but is otherwise ignored.
*
* @exception IllegalArgumentException If {@code readAheadLimit < 0}
* @exception IOException If an I/O error occurs
*/
public void mark(int readAheadLimit) throws IOException {
if (readAheadLimit < 0){
throw new IllegalArgumentException("Read-ahead limit < 0");
}
synchronized (lock) {
ensureOpen();
mark = next;
}
}
Resets the stream to the most recent mark, or to the beginning of the
string if it has never been marked.
Throws: - IOException – If an I/O error occurs
/**
* Resets the stream to the most recent mark, or to the beginning of the
* string if it has never been marked.
*
* @exception IOException If an I/O error occurs
*/
public void reset() throws IOException {
synchronized (lock) {
ensureOpen();
next = mark;
}
}
Closes the stream and releases any system resources associated with
it. Once the stream has been closed, further read(),
ready(), mark(), or reset() invocations will throw an IOException.
Closing a previously closed stream has no effect. This method will block
while there is another thread blocking on the reader.
/**
* Closes the stream and releases any system resources associated with
* it. Once the stream has been closed, further read(),
* ready(), mark(), or reset() invocations will throw an IOException.
* Closing a previously closed stream has no effect. This method will block
* while there is another thread blocking on the reader.
*/
public void close() {
synchronized (lock) {
str = null;
}
}
}