1 /* 2 * Copyright (c) 1995, 2006, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.io; 27 28 /** 29 * The <code>DataInput</code> interface provides 30 * for reading bytes from a binary stream and 31 * reconstructing from them data in any of 32 * the Java primitive types. There is also 33 * a 34 * facility for reconstructing a <code>String</code> 35 * from data in 36 * <a href="#modified-utf-8">modified UTF-8</a> 37 * format. 38 * <p> 39 * It is generally true of all the reading 40 * routines in this interface that if end of 41 * file is reached before the desired number 42 * of bytes has been read, an <code>EOFException</code> 43 * (which is a kind of <code>IOException</code>) 44 * is thrown. If any byte cannot be read for 45 * any reason other than end of file, an <code>IOException</code> 46 * other than <code>EOFException</code> is 47 * thrown. In particular, an <code>IOException</code> 48 * may be thrown if the input stream has been 49 * closed. 50 * 51 * <h4><a name="modified-utf-8">Modified UTF-8</a></h4> 52 * <p> 53 * Implementations of the DataInput and DataOutput interfaces represent 54 * Unicode strings in a format that is a slight modification of UTF-8. 55 * (For information regarding the standard UTF-8 format, see section 56 * <i>3.9 Unicode Encoding Forms</i> of <i>The Unicode Standard, Version 57 * 4.0</i>). 58 * Note that in the following tables, the most significant bit appears in the 59 * far left-hand column. 60 * <p> 61 * All characters in the range <code>'\u0001'</code> to 62 * <code>'\u007F'</code> are represented by a single byte: 63 * 64 * <blockquote> 65 * <table border="1" cellspacing="0" cellpadding="8" width="50%" 66 * summary="Bit values and bytes"> 67 * <tr> 68 * <td></td> 69 * <th id="bit">Bit Values</th> 70 * </tr> 71 * <tr> 72 * <th id="byte1">Byte 1</th> 73 * <td> 74 * <table border="1" cellspacing="0" width="100%"> 75 * <tr> 76 * <td width="12%"><center>0</center> 77 * <td colspan="7"><center>bits 6-0</center> 78 * </tr> 79 * </table> 80 * </td> 81 * </tr> 82 * </table> 83 * </blockquote> 84 * 85 * <p> 86 * The null character <code>'\u0000'</code> and characters in the 87 * range <code>'\u0080'</code> to <code>'\u07FF'</code> are 88 * represented by a pair of bytes: 89 * 90 * <blockquote> 91 * <table border="1" cellspacing="0" cellpadding="8" width="50%" 92 * summary="Bit values and bytes"> 93 * <tr> 94 * <td></td> 95 * <th id="bit">Bit Values</th> 96 * </tr> 97 * <tr> 98 * <th id="byte1">Byte 1</th> 99 * <td> 100 * <table border="1" cellspacing="0" width="100%"> 101 * <tr> 102 * <td width="12%"><center>1</center> 103 * <td width="13%"><center>1</center> 104 * <td width="12%"><center>0</center> 105 * <td colspan="5"><center>bits 10-6</center> 106 * </tr> 107 * </table> 108 * </td> 109 * </tr> 110 * <tr> 111 * <th id="byte2">Byte 2</th> 112 * <td> 113 * <table border="1" cellspacing="0" width="100%"> 114 * <tr> 115 * <td width="12%"><center>1</center> 116 * <td width="13%"><center>0</center> 117 * <td colspan="6"><center>bits 5-0</center> 118 * </tr> 119 * </table> 120 * </td> 121 * </tr> 122 * </table> 123 * </blockquote> 124 * 125 * <br> 126 * <code>char</code> values in the range <code>'\u0800'</code> to 127 * <code>'\uFFFF'</code> are represented by three bytes: 128 * 129 * <blockquote> 130 * <table border="1" cellspacing="0" cellpadding="8" width="50%" 131 * summary="Bit values and bytes"> 132 * <tr> 133 * <td></td> 134 * <th id="bit">Bit Values</th> 135 * </tr> 136 * <tr> 137 * <th id="byte1">Byte 1</th> 138 * <td> 139 * <table border="1" cellspacing="0" width="100%"> 140 * <tr> 141 * <td width="12%"><center>1</center> 142 * <td width="13%"><center>1</center> 143 * <td width="12%"><center>1</center> 144 * <td width="13%"><center>0</center> 145 * <td colspan="4"><center>bits 15-12</center> 146 * </tr> 147 * </table> 148 * </td> 149 * </tr> 150 * <tr> 151 * <th id="byte2">Byte 2</th> 152 * <td> 153 * <table border="1" cellspacing="0" width="100%"> 154 * <tr> 155 * <td width="12%"><center>1</center> 156 * <td width="13%"><center>0</center> 157 * <td colspan="6"><center>bits 11-6</center> 158 * </tr> 159 * </table> 160 * </td> 161 * </tr> 162 * <tr> 163 * <th id="byte3">Byte 3</th> 164 * <td> 165 * <table border="1" cellspacing="0" width="100%"> 166 * <tr> 167 * <td width="12%"><center>1</center> 168 * <td width="13%"><center>0</center> 169 * <td colspan="6"><center>bits 5-0</center> 170 * </tr> 171 * </table> 172 * </td> 173 * </tr> 174 * </table> 175 * </blockquote> 176 * 177 * <p> 178 * The differences between this format and the 179 * standard UTF-8 format are the following: 180 * <ul> 181 * <li>The null byte <code>'\u0000'</code> is encoded in 2-byte format 182 * rather than 1-byte, so that the encoded strings never have 183 * embedded nulls. 184 * <li>Only the 1-byte, 2-byte, and 3-byte formats are used. 185 * <li><a href="../lang/Character.html#unicode">Supplementary characters</a> 186 * are represented in the form of surrogate pairs. 187 * </ul> 188 * @author Frank Yellin 189 * @see java.io.DataInputStream 190 * @see java.io.DataOutput 191 * @since JDK1.0 192 */ 193 public 194 interface DataInput { 195 /** 196 * Reads some bytes from an input 197 * stream and stores them into the buffer 198 * array <code>b</code>. The number of bytes 199 * read is equal 200 * to the length of <code>b</code>. 201 * <p> 202 * This method blocks until one of the 203 * following conditions occurs:<p> 204 * <ul> 205 * <li><code>b.length</code> 206 * bytes of input data are available, in which 207 * case a normal return is made. 208 * 209 * <li>End of 210 * file is detected, in which case an <code>EOFException</code> 211 * is thrown. 212 * 213 * <li>An I/O error occurs, in 214 * which case an <code>IOException</code> other 215 * than <code>EOFException</code> is thrown. 216 * </ul> 217 * <p> 218 * If <code>b</code> is <code>null</code>, 219 * a <code>NullPointerException</code> is thrown. 220 * If <code>b.length</code> is zero, then 221 * no bytes are read. Otherwise, the first 222 * byte read is stored into element <code>b[0]</code>, 223 * the next one into <code>b[1]</code>, and 224 * so on. 225 * If an exception is thrown from 226 * this method, then it may be that some but 227 * not all bytes of <code>b</code> have been 228 * updated with data from the input stream. 229 * 230 * @param b the buffer into which the data is read. 231 * @exception EOFException if this stream reaches the end before reading 232 * all the bytes. 233 * @exception IOException if an I/O error occurs. 234 */ 235 void readFully(byte b[]) throws IOException; 236 237 /** 238 * 239 * Reads <code>len</code> 240 * bytes from 241 * an input stream. 242 * <p> 243 * This method 244 * blocks until one of the following conditions 245 * occurs:<p> 246 * <ul> 247 * <li><code>len</code> bytes 248 * of input data are available, in which case 249 * a normal return is made. 250 * 251 * <li>End of file 252 * is detected, in which case an <code>EOFException</code> 253 * is thrown. 254 * 255 * <li>An I/O error occurs, in 256 * which case an <code>IOException</code> other 257 * than <code>EOFException</code> is thrown. 258 * </ul> 259 * <p> 260 * If <code>b</code> is <code>null</code>, 261 * a <code>NullPointerException</code> is thrown. 262 * If <code>off</code> is negative, or <code>len</code> 263 * is negative, or <code>off+len</code> is 264 * greater than the length of the array <code>b</code>, 265 * then an <code>IndexOutOfBoundsException</code> 266 * is thrown. 267 * If <code>len</code> is zero, 268 * then no bytes are read. Otherwise, the first 269 * byte read is stored into element <code>b[off]</code>, 270 * the next one into <code>b[off+1]</code>, 271 * and so on. The number of bytes read is, 272 * at most, equal to <code>len</code>. 273 * 274 * @param b the buffer into which the data is read. 275 * @param off an int specifying the offset into the data. 276 * @param len an int specifying the number of bytes to read. 277 * @exception EOFException if this stream reaches the end before reading 278 * all the bytes. 279 * @exception IOException if an I/O error occurs. 280 */ 281 void readFully(byte b[], int off, int len) throws IOException; 282 283 /** 284 * Makes an attempt to skip over 285 * <code>n</code> bytes 286 * of data from the input 287 * stream, discarding the skipped bytes. However, 288 * it may skip 289 * over some smaller number of 290 * bytes, possibly zero. This may result from 291 * any of a 292 * number of conditions; reaching 293 * end of file before <code>n</code> bytes 294 * have been skipped is 295 * only one possibility. 296 * This method never throws an <code>EOFException</code>. 297 * The actual 298 * number of bytes skipped is returned. 299 * 300 * @param n the number of bytes to be skipped. 301 * @return the number of bytes actually skipped. 302 * @exception IOException if an I/O error occurs. 303 */ 304 int skipBytes(int n) throws IOException; 305 306 /** 307 * Reads one input byte and returns 308 * <code>true</code> if that byte is nonzero, 309 * <code>false</code> if that byte is zero. 310 * This method is suitable for reading 311 * the byte written by the <code>writeBoolean</code> 312 * method of interface <code>DataOutput</code>. 313 * 314 * @return the <code>boolean</code> value read. 315 * @exception EOFException if this stream reaches the end before reading 316 * all the bytes. 317 * @exception IOException if an I/O error occurs. 318 */ 319 boolean readBoolean() throws IOException; 320 321 /** 322 * Reads and returns one input byte. 323 * The byte is treated as a signed value in 324 * the range <code>-128</code> through <code>127</code>, 325 * inclusive. 326 * This method is suitable for 327 * reading the byte written by the <code>writeByte</code> 328 * method of interface <code>DataOutput</code>. 329 * 330 * @return the 8-bit value read. 331 * @exception EOFException if this stream reaches the end before reading 332 * all the bytes. 333 * @exception IOException if an I/O error occurs. 334 */ 335 byte readByte() throws IOException; 336 337 /** 338 * Reads one input byte, zero-extends 339 * it to type <code>int</code>, and returns 340 * the result, which is therefore in the range 341 * <code>0</code> 342 * through <code>255</code>. 343 * This method is suitable for reading 344 * the byte written by the <code>writeByte</code> 345 * method of interface <code>DataOutput</code> 346 * if the argument to <code>writeByte</code> 347 * was intended to be a value in the range 348 * <code>0</code> through <code>255</code>. 349 * 350 * @return the unsigned 8-bit value read. 351 * @exception EOFException if this stream reaches the end before reading 352 * all the bytes. 353 * @exception IOException if an I/O error occurs. 354 */ 355 int readUnsignedByte() throws IOException; 356 357 /** 358 * Reads two input bytes and returns 359 * a <code>short</code> value. Let <code>a</code> 360 * be the first byte read and <code>b</code> 361 * be the second byte. The value 362 * returned 363 * is: 364 * <p><pre><code>(short)((a << 8) | (b & 0xff)) 365 * </code></pre> 366 * This method 367 * is suitable for reading the bytes written 368 * by the <code>writeShort</code> method of 369 * interface <code>DataOutput</code>. 370 * 371 * @return the 16-bit value read. 372 * @exception EOFException if this stream reaches the end before reading 373 * all the bytes. 374 * @exception IOException if an I/O error occurs. 375 */ 376 short readShort() throws IOException; 377 378 /** 379 * Reads two input bytes and returns 380 * an <code>int</code> value in the range <code>0</code> 381 * through <code>65535</code>. Let <code>a</code> 382 * be the first byte read and 383 * <code>b</code> 384 * be the second byte. The value returned is: 385 * <p><pre><code>(((a & 0xff) << 8) | (b & 0xff)) 386 * </code></pre> 387 * This method is suitable for reading the bytes 388 * written by the <code>writeShort</code> method 389 * of interface <code>DataOutput</code> if 390 * the argument to <code>writeShort</code> 391 * was intended to be a value in the range 392 * <code>0</code> through <code>65535</code>. 393 * 394 * @return the unsigned 16-bit value read. 395 * @exception EOFException if this stream reaches the end before reading 396 * all the bytes. 397 * @exception IOException if an I/O error occurs. 398 */ 399 int readUnsignedShort() throws IOException; 400 401 /** 402 * Reads two input bytes and returns a <code>char</code> value. 403 * Let <code>a</code> 404 * be the first byte read and <code>b</code> 405 * be the second byte. The value 406 * returned is: 407 * <p><pre><code>(char)((a << 8) | (b & 0xff)) 408 * </code></pre> 409 * This method 410 * is suitable for reading bytes written by 411 * the <code>writeChar</code> method of interface 412 * <code>DataOutput</code>. 413 * 414 * @return the <code>char</code> value read. 415 * @exception EOFException if this stream reaches the end before reading 416 * all the bytes. 417 * @exception IOException if an I/O error occurs. 418 */ 419 char readChar() throws IOException; 420 421 /** 422 * Reads four input bytes and returns an 423 * <code>int</code> value. Let <code>a-d</code> 424 * be the first through fourth bytes read. The value returned is: 425 * <p><pre> 426 * <code> 427 * (((a & 0xff) << 24) | ((b & 0xff) << 16) | 428 *  ((c & 0xff) << 8) | (d & 0xff)) 429 * </code></pre> 430 * This method is suitable 431 * for reading bytes written by the <code>writeInt</code> 432 * method of interface <code>DataOutput</code>. 433 * 434 * @return the <code>int</code> value read. 435 * @exception EOFException if this stream reaches the end before reading 436 * all the bytes. 437 * @exception IOException if an I/O error occurs. 438 */ 439 int readInt() throws IOException; 440 441 /** 442 * Reads eight input bytes and returns 443 * a <code>long</code> value. Let <code>a-h</code> 444 * be the first through eighth bytes read. 445 * The value returned is: 446 * <p><pre> <code> 447 * (((long)(a & 0xff) << 56) | 448 * ((long)(b & 0xff) << 48) | 449 * ((long)(c & 0xff) << 40) | 450 * ((long)(d & 0xff) << 32) | 451 * ((long)(e & 0xff) << 24) | 452 * ((long)(f & 0xff) << 16) | 453 * ((long)(g & 0xff) << 8) | 454 * ((long)(h & 0xff))) 455 * </code></pre> 456 * <p> 457 * This method is suitable 458 * for reading bytes written by the <code>writeLong</code> 459 * method of interface <code>DataOutput</code>. 460 * 461 * @return the <code>long</code> value read. 462 * @exception EOFException if this stream reaches the end before reading 463 * all the bytes. 464 * @exception IOException if an I/O error occurs. 465 */ 466 long readLong() throws IOException; 467 468 /** 469 * Reads four input bytes and returns 470 * a <code>float</code> value. It does this 471 * by first constructing an <code>int</code> 472 * value in exactly the manner 473 * of the <code>readInt</code> 474 * method, then converting this <code>int</code> 475 * value to a <code>float</code> in 476 * exactly the manner of the method <code>Float.intBitsToFloat</code>. 477 * This method is suitable for reading 478 * bytes written by the <code>writeFloat</code> 479 * method of interface <code>DataOutput</code>. 480 * 481 * @return the <code>float</code> value read. 482 * @exception EOFException if this stream reaches the end before reading 483 * all the bytes. 484 * @exception IOException if an I/O error occurs. 485 */ 486 float readFloat() throws IOException; 487 488 /** 489 * Reads eight input bytes and returns 490 * a <code>double</code> value. It does this 491 * by first constructing a <code>long</code> 492 * value in exactly the manner 493 * of the <code>readlong</code> 494 * method, then converting this <code>long</code> 495 * value to a <code>double</code> in exactly 496 * the manner of the method <code>Double.longBitsToDouble</code>. 497 * This method is suitable for reading 498 * bytes written by the <code>writeDouble</code> 499 * method of interface <code>DataOutput</code>. 500 * 501 * @return the <code>double</code> value read. 502 * @exception EOFException if this stream reaches the end before reading 503 * all the bytes. 504 * @exception IOException if an I/O error occurs. 505 */ 506 double readDouble() throws IOException; 507 508 /** 509 * Reads the next line of text from the input stream. 510 * It reads successive bytes, converting 511 * each byte separately into a character, 512 * until it encounters a line terminator or 513 * end of 514 * file; the characters read are then 515 * returned as a <code>String</code>. Note 516 * that because this 517 * method processes bytes, 518 * it does not support input of the full Unicode 519 * character set. 520 * <p> 521 * If end of file is encountered 522 * before even one byte can be read, then <code>null</code> 523 * is returned. Otherwise, each byte that is 524 * read is converted to type <code>char</code> 525 * by zero-extension. If the character <code>'\n'</code> 526 * is encountered, it is discarded and reading 527 * ceases. If the character <code>'\r'</code> 528 * is encountered, it is discarded and, if 529 * the following byte converts  to the 530 * character <code>'\n'</code>, then that is 531 * discarded also; reading then ceases. If 532 * end of file is encountered before either 533 * of the characters <code>'\n'</code> and 534 * <code>'\r'</code> is encountered, reading 535 * ceases. Once reading has ceased, a <code>String</code> 536 * is returned that contains all the characters 537 * read and not discarded, taken in order. 538 * Note that every character in this string 539 * will have a value less than <code>\u0100</code>, 540 * that is, <code>(char)256</code>. 541 * 542 * @return the next line of text from the input stream, 543 * or <CODE>null</CODE> if the end of file is 544 * encountered before a byte can be read. 545 * @exception IOException if an I/O error occurs. 546 */ 547 String readLine() throws IOException; 548 549 /** 550 * Reads in a string that has been encoded using a 551 * <a href="#modified-utf-8">modified UTF-8</a> 552 * format. 553 * The general contract of <code>readUTF</code> 554 * is that it reads a representation of a Unicode 555 * character string encoded in modified 556 * UTF-8 format; this string of characters 557 * is then returned as a <code>String</code>. 558 * <p> 559 * First, two bytes are read and used to 560 * construct an unsigned 16-bit integer in 561 * exactly the manner of the <code>readUnsignedShort</code> 562 * method . This integer value is called the 563 * <i>UTF length</i> and specifies the number 564 * of additional bytes to be read. These bytes 565 * are then converted to characters by considering 566 * them in groups. The length of each group 567 * is computed from the value of the first 568 * byte of the group. The byte following a 569 * group, if any, is the first byte of the 570 * next group. 571 * <p> 572 * If the first byte of a group 573 * matches the bit pattern <code>0xxxxxxx</code> 574 * (where <code>x</code> means "may be <code>0</code> 575 * or <code>1</code>"), then the group consists 576 * of just that byte. The byte is zero-extended 577 * to form a character. 578 * <p> 579 * If the first byte 580 * of a group matches the bit pattern <code>110xxxxx</code>, 581 * then the group consists of that byte <code>a</code> 582 * and a second byte <code>b</code>. If there 583 * is no byte <code>b</code> (because byte 584 * <code>a</code> was the last of the bytes 585 * to be read), or if byte <code>b</code> does 586 * not match the bit pattern <code>10xxxxxx</code>, 587 * then a <code>UTFDataFormatException</code> 588 * is thrown. Otherwise, the group is converted 589 * to the character:<p> 590 * <pre><code>(char)(((a& 0x1F) << 6) | (b & 0x3F)) 591 * </code></pre> 592 * If the first byte of a group 593 * matches the bit pattern <code>1110xxxx</code>, 594 * then the group consists of that byte <code>a</code> 595 * and two more bytes <code>b</code> and <code>c</code>. 596 * If there is no byte <code>c</code> (because 597 * byte <code>a</code> was one of the last 598 * two of the bytes to be read), or either 599 * byte <code>b</code> or byte <code>c</code> 600 * does not match the bit pattern <code>10xxxxxx</code>, 601 * then a <code>UTFDataFormatException</code> 602 * is thrown. Otherwise, the group is converted 603 * to the character:<p> 604 * <pre><code> 605 * (char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F)) 606 * </code></pre> 607 * If the first byte of a group matches the 608 * pattern <code>1111xxxx</code> or the pattern 609 * <code>10xxxxxx</code>, then a <code>UTFDataFormatException</code> 610 * is thrown. 611 * <p> 612 * If end of file is encountered 613 * at any time during this entire process, 614 * then an <code>EOFException</code> is thrown. 615 * <p> 616 * After every group has been converted to 617 * a character by this process, the characters 618 * are gathered, in the same order in which 619 * their corresponding groups were read from 620 * the input stream, to form a <code>String</code>, 621 * which is returned. 622 * <p> 623 * The <code>writeUTF</code> 624 * method of interface <code>DataOutput</code> 625 * may be used to write data that is suitable 626 * for reading by this method. 627 * @return a Unicode string. 628 * @exception EOFException if this stream reaches the end 629 * before reading all the bytes. 630 * @exception IOException if an I/O error occurs. 631 * @exception UTFDataFormatException if the bytes do not represent a 632 * valid modified UTF-8 encoding of a string. 633 */ 634 String readUTF() throws IOException; 635 }