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25 
26 package java.io;
27 
28 
29 /**
30  * A character stream whose source is a string.
31  *
32  * @author      Mark Reinhold
33  * @since       JDK1.1
34  */
35 
36 public class StringReader extends Reader {
37 
38     private String str;
39     private int length;
40     private int next = 0;
41     private int mark = 0;
42 
43     /**
44      * Creates a new string reader.
45      *
46      * @param s  String providing the character stream.
47      */
StringReader(String s)48     public StringReader(String s) {
49         this.str = s;
50         this.length = s.length();
51     }
52 
53     /** Check to make sure that the stream has not been closed */
ensureOpen()54     private void ensureOpen() throws IOException {
55         if (str == null)
56             throw new IOException("Stream closed");
57     }
58 
59     /**
60      * Reads a single character.
61      *
62      * @return     The character read, or -1 if the end of the stream has been
63      *             reached
64      *
65      * @exception  IOException  If an I/O error occurs
66      */
read()67     public int read() throws IOException {
68         synchronized (lock) {
69             ensureOpen();
70             if (next >= length)
71                 return -1;
72             return str.charAt(next++);
73         }
74     }
75 
76     /**
77      * Reads characters into a portion of an array.
78      *
79      * @param      cbuf  Destination buffer
80      * @param      off   Offset at which to start writing characters
81      * @param      len   Maximum number of characters to read
82      *
83      * @return     The number of characters read, or -1 if the end of the
84      *             stream has been reached
85      *
86      * @exception  IOException  If an I/O error occurs
87      */
read(char cbuf[], int off, int len)88     public int read(char cbuf[], int off, int len) throws IOException {
89         synchronized (lock) {
90             ensureOpen();
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) {
95                 return 0;
96             }
97             if (next >= length)
98                 return -1;
99             int n = Math.min(length - next, len);
100             str.getChars(next, next + n, cbuf, off);
101             next += n;
102             return n;
103         }
104     }
105 
106     /**
107      * Skips the specified number of characters in the stream. Returns
108      * the number of characters that were skipped.
109      *
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
115      * the string.
116      *
117      * <p>If the entire string has been read or skipped, then this method has
118      * no effect and always returns 0.
119      *
120      * @exception  IOException  If an I/O error occurs
121      */
skip(long ns)122     public long skip(long ns) throws IOException {
123         synchronized (lock) {
124             ensureOpen();
125             if (next >= length)
126                 return 0;
127             // Bound skip by beginning and end of the source
128             long n = Math.min(length - next, ns);
129             n = Math.max(-next, n);
130             next += n;
131             return n;
132         }
133     }
134 
135     /**
136      * Tells whether this stream is ready to be read.
137      *
138      * @return True if the next read() is guaranteed not to block for input
139      *
140      * @exception  IOException  If the stream is closed
141      */
ready()142     public boolean ready() throws IOException {
143         synchronized (lock) {
144         ensureOpen();
145         return true;
146         }
147     }
148 
149     /**
150      * Tells whether this stream supports the mark() operation, which it does.
151      */
markSupported()152     public boolean markSupported() {
153         return true;
154     }
155 
156     /**
157      * Marks the present position in the stream.  Subsequent calls to reset()
158      * will reposition the stream to this point.
159      *
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.
165      *
166      * @exception  IllegalArgumentException  If {@code readAheadLimit < 0}
167      * @exception  IOException  If an I/O error occurs
168      */
mark(int readAheadLimit)169     public void mark(int readAheadLimit) throws IOException {
170         if (readAheadLimit < 0){
171             throw new IllegalArgumentException("Read-ahead limit < 0");
172         }
173         synchronized (lock) {
174             ensureOpen();
175             mark = next;
176         }
177     }
178 
179     /**
180      * Resets the stream to the most recent mark, or to the beginning of the
181      * string if it has never been marked.
182      *
183      * @exception  IOException  If an I/O error occurs
184      */
reset()185     public void reset() throws IOException {
186         synchronized (lock) {
187             ensureOpen();
188             next = mark;
189         }
190     }
191 
192     /**
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.
197      */
close()198     public void close() {
199         str = null;
200     }
201 }
202