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30 * A character stream whose source is a string.
32 * @author Mark Reinhold
36 public class StringReader extends Reader {
44 * Creates a new string reader.
46 * @param s String providing the character stream.
48 public StringReader(String s) {
50 this.length = s.length();
53 /** Check to make sure that the stream has not been closed */
54 private void ensureOpen() throws IOException {
56 throw new IOException("Stream closed");
60 * Reads a single character.
62 * @return The character read, or -1 if the end of the stream has been
65 * @exception IOException If an I/O error occurs
67 public int read() throws IOException {
72 return str.charAt(next++);
77 * Reads characters into a portion of an array.
79 * @param cbuf Destination buffer
80 * @param off Offset at which to start writing characters
81 * @param len Maximum number of characters to read
83 * @return The number of characters read, or -1 if the end of the
84 * stream has been reached
86 * @exception IOException If an I/O error occurs
88 public int read(char cbuf[], int off, int len) throws IOException {
91 if ((off < 0) || (off > cbuf.length) || (len < 0) ||
92 ((off + len) > cbuf.length) || ((off + len) < 0)) {
93 throw new IndexOutOfBoundsException();
94 } else if (len == 0) {
99 int n = Math.min(length - next, len);
100 str.getChars(next, next + n, cbuf, off);
107 * Skips the specified number of characters in the stream. Returns
108 * the number of characters that were skipped.
110 * <p>The <code>ns</code> parameter may be negative, even though the
111 * <code>skip</code> method of the {@link Reader} superclass throws
112 * an exception in this case. Negative values of <code>ns</code> cause the
113 * stream to skip backwards. Negative return values indicate a skip
114 * backwards. It is not possible to skip backwards past the beginning of
117 * <p>If the entire string has been read or skipped, then this method has
118 * no effect and always returns 0.
120 * @exception IOException If an I/O error occurs
122 public long skip(long ns) throws IOException {
123 synchronized (lock) {
127 // Bound skip by beginning and end of the source
128 long n = Math.min(length - next, ns);
129 n = Math.max(-next, n);
136 * Tells whether this stream is ready to be read.
138 * @return True if the next read() is guaranteed not to block for input
140 * @exception IOException If the stream is closed
142 public boolean ready() throws IOException {
143 synchronized (lock) {
150 * Tells whether this stream supports the mark() operation, which it does.
152 public boolean markSupported() {
157 * Marks the present position in the stream. Subsequent calls to reset()
158 * will reposition the stream to this point.
160 * @param readAheadLimit Limit on the number of characters that may be
161 * read while still preserving the mark. Because
162 * the stream's input comes from a string, there
163 * is no actual limit, so this argument must not
164 * be negative, but is otherwise ignored.
166 * @exception IllegalArgumentException If readAheadLimit is < 0
167 * @exception IOException If an I/O error occurs
169 public void mark(int readAheadLimit) throws IOException {
170 if (readAheadLimit < 0){
171 throw new IllegalArgumentException("Read-ahead limit < 0");
173 synchronized (lock) {
180 * Resets the stream to the most recent mark, or to the beginning of the
181 * string if it has never been marked.
183 * @exception IOException If an I/O error occurs
185 public void reset() throws IOException {
186 synchronized (lock) {
193 * Closes the stream and releases any system resources associated with
194 * it. Once the stream has been closed, further read(),
195 * ready(), mark(), or reset() invocations will throw an IOException.
196 * Closing a previously closed stream has no effect.
198 public void close() {