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25 
26 package java.io;
27 
28 /**
29  * This class implements a character buffer that can be used as a
30  * character-input stream.
31  *
32  * @author      Herb Jellinek
33  * @since       JDK1.1
34  */
35 public class CharArrayReader extends Reader {
36     /** The character buffer. */
37     protected char buf[];
38 
39     /** The current buffer position. */
40     protected int pos;
41 
42     /** The position of mark in buffer. */
43     protected int markedPos = 0;
44 
45     /**
46      *  The index of the end of this buffer.  There is not valid
47      *  data at or beyond this index.
48      */
49     protected int count;
50 
51     /**
52      * Creates a CharArrayReader from the specified array of chars.
53      * @param buf       Input buffer (not copied)
54      */
CharArrayReader(char buf[])55     public CharArrayReader(char buf[]) {
56         this.buf = buf;
57         this.pos = 0;
58         this.count = buf.length;
59     }
60 
61     /**
62      * Creates a CharArrayReader from the specified array of chars.
63      *
64      * <p> The resulting reader will start reading at the given
65      * <tt>offset</tt>.  The total number of <tt>char</tt> values that can be
66      * read from this reader will be either <tt>length</tt> or
67      * <tt>buf.length-offset</tt>, whichever is smaller.
68      *
69      * @throws IllegalArgumentException
70      *         If <tt>offset</tt> is negative or greater than
71      *         <tt>buf.length</tt>, or if <tt>length</tt> is negative, or if
72      *         the sum of these two values is negative.
73      *
74      * @param buf       Input buffer (not copied)
75      * @param offset    Offset of the first char to read
76      * @param length    Number of chars to read
77      */
CharArrayReader(char buf[], int offset, int length)78     public CharArrayReader(char buf[], int offset, int length) {
79         if ((offset < 0) || (offset > buf.length) || (length < 0) ||
80             ((offset + length) < 0)) {
81             throw new IllegalArgumentException();
82         }
83         this.buf = buf;
84         this.pos = offset;
85         this.count = Math.min(offset + length, buf.length);
86         this.markedPos = offset;
87     }
88 
89     /** Checks to make sure that the stream has not been closed */
ensureOpen()90     private void ensureOpen() throws IOException {
91         if (buf == null)
92             throw new IOException("Stream closed");
93     }
94 
95     /**
96      * Reads a single character.
97      *
98      * @exception   IOException  If an I/O error occurs
99      */
read()100     public int read() throws IOException {
101         synchronized (lock) {
102             ensureOpen();
103             if (pos >= count)
104                 return -1;
105             else
106                 return buf[pos++];
107         }
108     }
109 
110     /**
111      * Reads characters into a portion of an array.
112      * @param b  Destination buffer
113      * @param off  Offset at which to start storing characters
114      * @param len   Maximum number of characters to read
115      * @return  The actual number of characters read, or -1 if
116      *          the end of the stream has been reached
117      *
118      * @exception   IOException  If an I/O error occurs
119      */
read(char b[], int off, int len)120     public int read(char b[], int off, int len) throws IOException {
121         synchronized (lock) {
122             ensureOpen();
123             if ((off < 0) || (off > b.length) || (len < 0) ||
124                 ((off + len) > b.length) || ((off + len) < 0)) {
125                 throw new IndexOutOfBoundsException();
126             } else if (len == 0) {
127                 return 0;
128             }
129 
130             if (pos >= count) {
131                 return -1;
132             }
133 
134             int avail = count - pos;
135             if (len > avail) {
136                 len = avail;
137             }
138             if (len <= 0) {
139                 return 0;
140             }
141             System.arraycopy(buf, pos, b, off, len);
142             pos += len;
143             return len;
144         }
145     }
146 
147     /**
148      * Skips characters.  Returns the number of characters that were skipped.
149      *
150      * <p>The <code>n</code> parameter may be negative, even though the
151      * <code>skip</code> method of the {@link Reader} superclass throws
152      * an exception in this case. If <code>n</code> is negative, then
153      * this method does nothing and returns <code>0</code>.
154      *
155      * @param n The number of characters to skip
156      * @return       The number of characters actually skipped
157      * @exception  IOException If the stream is closed, or an I/O error occurs
158      */
skip(long n)159     public long skip(long n) throws IOException {
160         synchronized (lock) {
161             ensureOpen();
162 
163             long avail = count - pos;
164             if (n > avail) {
165                 n = avail;
166             }
167             if (n < 0) {
168                 return 0;
169             }
170             pos += n;
171             return n;
172         }
173     }
174 
175     /**
176      * Tells whether this stream is ready to be read.  Character-array readers
177      * are always ready to be read.
178      *
179      * @exception  IOException  If an I/O error occurs
180      */
ready()181     public boolean ready() throws IOException {
182         synchronized (lock) {
183             ensureOpen();
184             return (count - pos) > 0;
185         }
186     }
187 
188     /**
189      * Tells whether this stream supports the mark() operation, which it does.
190      */
markSupported()191     public boolean markSupported() {
192         return true;
193     }
194 
195     /**
196      * Marks the present position in the stream.  Subsequent calls to reset()
197      * will reposition the stream to this point.
198      *
199      * @param  readAheadLimit  Limit on the number of characters that may be
200      *                         read while still preserving the mark.  Because
201      *                         the stream's input comes from a character array,
202      *                         there is no actual limit; hence this argument is
203      *                         ignored.
204      *
205      * @exception  IOException  If an I/O error occurs
206      */
mark(int readAheadLimit)207     public void mark(int readAheadLimit) throws IOException {
208         synchronized (lock) {
209             ensureOpen();
210             markedPos = pos;
211         }
212     }
213 
214     /**
215      * Resets the stream to the most recent mark, or to the beginning if it has
216      * never been marked.
217      *
218      * @exception  IOException  If an I/O error occurs
219      */
reset()220     public void reset() throws IOException {
221         synchronized (lock) {
222             ensureOpen();
223             pos = markedPos;
224         }
225     }
226 
227     /**
228      * Closes the stream and releases any system resources associated with
229      * it.  Once the stream has been closed, further read(), ready(),
230      * mark(), reset(), or skip() invocations will throw an IOException.
231      * Closing a previously closed stream has no effect.
232      */
close()233     public void close() {
234         buf = null;
235     }
236 }
237