001/* DataInput.java -- Interface for reading data from a stream 002 Copyright (C) 1998, 1999, 2001, 2003, 2005 Free Software Foundation, Inc. 003 004This file is part of GNU Classpath. 005 006GNU Classpath is free software; you can redistribute it and/or modify 007it under the terms of the GNU General Public License as published by 008the Free Software Foundation; either version 2, or (at your option) 009any later version. 010 011GNU Classpath is distributed in the hope that it will be useful, but 012WITHOUT ANY WARRANTY; without even the implied warranty of 013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014General Public License for more details. 015 016You should have received a copy of the GNU General Public License 017along with GNU Classpath; see the file COPYING. If not, write to the 018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 01902110-1301 USA. 020 021Linking this library statically or dynamically with other modules is 022making a combined work based on this library. Thus, the terms and 023conditions of the GNU General Public License cover the whole 024combination. 025 026As a special exception, the copyright holders of this library give you 027permission to link this library with independent modules to produce an 028executable, regardless of the license terms of these independent 029modules, and to copy and distribute the resulting executable under 030terms of your choice, provided that you also meet, for each linked 031independent module, the terms and conditions of the license of that 032module. An independent module is a module which is not derived from 033or based on this library. If you modify this library, you may extend 034this exception to your version of the library, but you are not 035obligated to do so. If you do not wish to do so, delete this 036exception statement from your version. */ 037 038 039package java.io; 040 041/* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3 042 * "The Java Language Specification", ISBN 0-201-63451-1 043 * plus online API docs for JDK 1.2 beta from http://www.javasoft.com. 044 * Status: Believed complete and correct. */ 045 046/** 047 * This interface is implemented by classes that can data from streams 048 * into Java primitive types. 049 * 050 * @author Aaron M. Renn (arenn@urbanophile.com) 051 * @author Warren Levy (warrenl@cygnus.com) 052 */ 053public interface DataInput 054{ 055 056 /** 057 * This method reads a Java boolean value from an input stream. It does 058 * so by reading a single byte of data. If that byte is zero, then the 059 * value returned is <code>false</code>. If the byte is non-zero, then 060 * the value returned is <code>true</code>. 061 * <p> 062 * This method can read a <code>boolean</code> written by an object 063 * implementing the <code>writeBoolean()</code> method in the 064 * <code>DataOutput</code> interface. 065 * 066 * @return The <code>boolean</code> value read 067 * 068 * @exception EOFException If end of file is reached before 069 * reading the boolean 070 * @exception IOException If any other error occurs 071 * 072 * @see DataOutput#writeBoolean 073 */ 074 boolean readBoolean() throws EOFException, IOException; 075 076 /** 077 * This method reads a Java byte value from an input stream. The value 078 * is in the range of -128 to 127. 079 * <p> 080 * This method can read a <code>byte</code> written by an object 081 * implementing the 082 * <code>writeByte()</code> method in the <code>DataOutput</code> interface. 083 * <p> 084 * @return The <code>byte</code> value read 085 * 086 * @exception EOFException If end of file is reached before reading the byte 087 * @exception IOException If any other error occurs 088 * 089 * @see DataOutput#writeByte 090 */ 091 byte readByte() throws EOFException, IOException; 092 093 /** 094 * This method reads 8 unsigned bits into a Java <code>int</code> value from 095 * the stream. The value returned is in the range of 0 to 255. 096 * <p> 097 * This method can read an unsigned byte written by an object 098 * implementing the 099 * <code>writeByte()</code> method in the <code>DataOutput</code> 100 * interface. 101 * 102 * @return The unsigned bytes value read as a Java <code>int</code>. 103 * 104 * @exception EOFException If end of file is reached before reading the value 105 * @exception IOException If any other error occurs 106 * 107 * @see DataOutput#writeByte 108 */ 109 int readUnsignedByte() throws EOFException, IOException; 110 111 /** 112 * This method reads a Java <code>char</code> value from an input stream. 113 * It operates by reading two bytes from the stream and converting them to 114 * a single 16-bit Java <code>char</code>. The two bytes are stored most 115 * significant byte first (i.e., "big endian") regardless of the native 116 * host byte ordering. 117 * <p> 118 * As an example, if <code>byte1</code> and <code>byte2</code> represent the 119 * first and second byte read from the stream respectively, they will be 120 * transformed to a <code>char</code> in the following manner: 121 * <p> 122 * <code>(char)((byte1 << 8) + byte2)</code> 123 * <p> 124 * This method can read a <code>char</code> written by an object implementing 125 * the 126 * <code>writeChar()</code> method in the <code>DataOutput</code> interface. 127 * 128 * @return The <code>char</code> value read 129 * 130 * @exception EOFException If end of file is reached before reading the char 131 * @exception IOException If any other error occurs 132 * 133 * @see DataOutput#writeChar 134 */ 135 char readChar() throws EOFException, IOException; 136 137 /** 138 * This method reads a signed 16-bit value into a Java in from the stream. 139 * It operates by reading two bytes from the stream and converting them to 140 * a single 16-bit Java <code>short</code>. The two bytes are stored most 141 * significant byte first (i.e., "big endian") regardless of the native 142 * host byte ordering. 143 * <p> 144 * As an example, if <code>byte1</code> and <code>byte2</code> represent the 145 * first and second byte read from the stream respectively, they will be 146 * transformed to a <code>short</code> in the following manner: 147 * <p> 148 * <code>(short)(((byte1 & 0xFF) << 8) + (byte2 & 0xFF))</code> 149 * <p> 150 * The value returned is in the range of -32768 to 32767. 151 * <p> 152 * This method can read a <code>short</code> written by an object 153 * implementing 154 * the <code>writeShort()</code> method in the <code>DataOutput</code> 155 * interface. 156 * 157 * @return The <code>short</code> value read 158 * 159 * @exception EOFException If end of file is reached before reading the value 160 * @exception IOException If any other error occurs 161 * 162 * @see DataOutput#writeShort 163 */ 164 short readShort() throws EOFException, IOException; 165 166 /** 167 * This method reads 16 unsigned bits into a Java int value from the stream. 168 * It operates by reading two bytes from the stream and converting them to 169 * a single Java <code>int</code>. The two bytes are stored most 170 * significant byte first (i.e., "big endian") regardless of the native 171 * host byte ordering. 172 * <p> 173 * As an example, if <code>byte1</code> and <code>byte2</code> represent the 174 * first and second byte read from the stream respectively, they will be 175 * transformed to an <code>int</code> in the following manner: 176 * <p> 177 * <code>(int)(((byte1 0xFF) << 8) + (byte2 & 0xFF))</code> 178 * <p> 179 * The value returned is in the range of 0 to 65535. 180 * <p> 181 * This method can read an unsigned short written by an object implementing 182 * the <code>writeShort()</code> method in the 183 * <code>DataOutput</code> 184 * interface. 185 * 186 * @return The unsigned short value read as a Java <code>int</code>. 187 * 188 * @exception EOFException If end of file is reached before reading 189 * the value 190 * @exception IOException If any other error occurs 191 * 192 * @see DataOutput#writeShort 193 */ 194 int readUnsignedShort() throws EOFException, IOException; 195 196 /** 197 * This method reads a Java <code>int</code> value from an input stream 198 * It operates by reading four bytes from the stream and converting them to 199 * a single Java <code>int</code>. The bytes are stored most 200 * significant byte first (i.e., "big endian") regardless of the native 201 * host byte ordering. 202 * <p> 203 * As an example, if <code>byte1</code> through <code>byte4</code> represent 204 * the first four bytes read from the stream, they will be 205 * transformed to an <code>int</code> in the following manner: 206 * <p> 207 * <code>(int)(((byte1 & 0xFF) << 24) + ((byte2 & 0xFF) << 16) + 208 * ((byte3 & 0xFF)<< 8) + (byte4 & 0xFF)))</code> 209 * <p> 210 * The value returned is in the range of -2147483648 to 2147483647. 211 * <p> 212 * This method can read an <code>int</code> written by an object 213 * implementing the <code>writeInt()</code> method in the 214 * <code>DataOutput</code> interface. 215 * 216 * @return The <code>int</code> value read 217 * 218 * @exception EOFException If end of file is reached before reading the int 219 * @exception IOException If any other error occurs 220 * 221 * @see DataOutput#writeInt 222 */ 223 int readInt() throws EOFException, IOException; 224 225 /** 226 * This method reads a Java <code>long</code> value from an input stream 227 * It operates by reading eight bytes from the stream and converting them to 228 * a single Java <code>long</code>. The bytes are stored most 229 * significant byte first (i.e., "big endian") regardless of the native 230 * host byte ordering. 231 * <p> 232 * As an example, if <code>byte1</code> through <code>byte8</code> represent 233 * the first eight bytes read from the stream, they will be 234 * transformed to an <code>long</code> in the following manner: 235 * <p> 236 * <code>(long)(((byte1 & 0xFF) << 56) + ((byte2 & 0xFF) << 48) + 237 * ((byte3 & 0xFF) << 40) + ((byte4 & 0xFF) << 32) + 238 * ((byte5 & 0xFF) << 24) + ((byte6 & 0xFF) << 16) + 239 * ((byte7 & 0xFF) << 8) + (byte8 & 0xFF))) 240 * </code> 241 * <p> 242 * The value returned is in the range of -9223372036854775808 to 243 * 9223372036854775807. 244 * <p> 245 * This method can read an <code>long</code> written by an object 246 * implementing the <code>writeLong()</code> method in the 247 * <code>DataOutput</code> interface. 248 * 249 * @return The <code>long</code> value read 250 * 251 * @exception EOFException If end of file is reached before reading the long 252 * @exception IOException If any other error occurs 253 * 254 * @see DataOutput#writeLong 255 */ 256 long readLong() throws EOFException, IOException; 257 258 /** 259 * This method reads a Java float value from an input stream. It operates 260 * by first reading an <code>int</code> value from the stream by calling the 261 * <code>readInt()</code> method in this interface, then converts that 262 * <code>int</code> to a <code>float</code> using the 263 * <code>intBitsToFloat</code> method in the class 264 * <code>java.lang.Float</code>. 265 * <p> 266 * This method can read a <code>float</code> written by an object 267 * implementing 268 * the <code>writeFloat()</code> method in the <code>DataOutput</code> 269 * interface. 270 * 271 * @return The <code>float</code> value read 272 * 273 * @exception EOFException If end of file is reached before reading the 274 * float 275 * @exception IOException If any other error occurs 276 * 277 * @see DataOutput#writeFloat 278 * @see java.lang.Float#intBitsToFloat 279 */ 280 float readFloat() throws EOFException, IOException; 281 282 /** 283 * This method reads a Java double value from an input stream. It operates 284 * by first reading a <code>long</code> value from the stream by calling the 285 * <code>readLong()</code> method in this interface, then converts that 286 * <code>long</code> to a <code>double</code> using the 287 * <code>longBitsToDouble</code> method in the class 288 * <code>java.lang.Double</code>. 289 * <p> 290 * This method can read a <code>double</code> written by an object 291 * implementing the <code>writeDouble()</code> method in the 292 * <code>DataOutput</code> interface. 293 * 294 * @return The <code>double</code> value read 295 * 296 * @exception EOFException If end of file is reached before reading the 297 * double 298 * @exception IOException If any other error occurs 299 * 300 * @see DataOutput#writeDouble 301 * @see java.lang.Double#longBitsToDouble 302 */ 303 double readDouble() throws EOFException, IOException; 304 305 /** 306 * This method reads the next line of text data from an input stream. 307 * It operates by reading bytes and converting those bytes to 308 * <code>char</code> 309 * values by treating the byte read as the low eight bits of the 310 * <code>char</code> and using 0 as the high eight bits. Because of this, 311 * it does not support the full 16-bit Unicode character set. 312 * <P> 313 * The reading of bytes ends when either the end of file or a line terminator 314 * is encountered. The bytes read are then returned as a 315 * <code>String</code>. 316 * A line terminator is a byte sequence consisting of either 317 * <code>\r</code>, <code>\n</code> or <code>\r\n</code>. These termination 318 * charaters are discarded and are not returned as part of the string. 319 * A line is also terminated by an end of file condition. 320 * <p> 321 * 322 * @return The line read as a <code>String</code> 323 * 324 * @exception IOException If an error occurs 325 */ 326 String readLine() throws IOException; 327 328 /** 329 * This method reads a <code>String</code> from an input stream that is 330 * encoded in a modified UTF-8 format. This format has a leading two byte 331 * sequence that contains the remaining number of bytes to read. 332 * This two byte 333 * sequence is read using the <code>readUnsignedShort()</code> method of this 334 * interface. 335 * 336 * After the number of remaining bytes have been determined, these bytes 337 * are read an transformed into <code>char</code> values. These 338 * <code>char</code> values are encoded in the stream using either a one, 339 * two, or three byte format. 340 * The particular format in use can be determined by examining the first 341 * byte read. 342 * <p> 343 * If the first byte has a high order bit of 0, then 344 * that character consists on only one byte. This character value consists 345 * of seven bits that are at positions 0 through 6 of the byte. As an 346 * example, if <code>byte1</code> is the byte read from the stream, it would 347 * be converted to a <code>char</code> like so: 348 * <p> 349 * <code>(char)byte1</code> 350 * <p> 351 * If the first byte has 110 as its high order bits, then the 352 * character consists of two bytes. The bits that make up the character 353 * value are in positions 0 through 4 of the first byte and bit positions 354 * 0 through 5 of the second byte. (The second byte should have 355 * 10 as its high order bits). These values are in most significant 356 * byte first (i.e., "big endian") order. 357 * <p> 358 * As an example, if <code>byte1</code> and <code>byte2</code> are the first 359 * two bytes read respectively, and the high order bits of them match the 360 * patterns which indicate a two byte character encoding, then they would be 361 * converted to a Java <code>char</code> like so: 362 * <p> 363 * <code>(char)(((byte1 & 0x1F) << 6) + (byte2 & 0x3F))</code> 364 * <p> 365 * If the first byte has a 1110 as its high order bits, then the 366 * character consists of three bytes. The bits that make up the character 367 * value are in positions 0 through 3 of the first byte and bit positions 368 * 0 through 5 of the other two bytes. (The second and third bytes should 369 * have 10 as their high order bits). These values are in most 370 * significant byte first (i.e., "big endian") order. 371 * <p> 372 * As an example, if <code>byte1</code>, <code>byte2</code>, and 373 * <code>byte3</code> are the three bytes read, and the high order bits of 374 * them match the patterns which indicate a three byte character encoding, 375 * then they would be converted to a Java <code>char</code> like so: 376 * 377 * <code> 378 * (char)(((byte1 & 0x0F) << 12) + ((byte2 & 0x3F) + (byte3 & 0x3F)) 379 * </code> 380 * 381 * Note that all characters are encoded in the method that requires the 382 * fewest number of bytes with the exception of the character with the 383 * value of <code>\<llll>u0000</code> which is encoded as two bytes. 384 * This is a modification of the UTF standard used to prevent C language 385 * style <code>NUL</code> values from appearing in the byte stream. 386 * <p> 387 * This method can read data that was written by an object implementing the 388 * <code>writeUTF()</code> method in <code>DataOutput</code>. 389 * 390 * @return The <code>String</code> read 391 * 392 * @exception EOFException If end of file is reached before reading the 393 * String 394 * @exception UTFDataFormatException If the data is not in UTF-8 format 395 * @exception IOException If any other error occurs 396 * 397 * @see DataOutput#writeUTF 398 */ 399 String readUTF() throws EOFException, UTFDataFormatException, IOException; 400 401 /** 402 * This method reads raw bytes into the passed array until the array is 403 * full. Note that this method blocks until the data is available and 404 * throws an exception if there is not enough data left in the stream to 405 * fill the buffer. Note also that zero length buffers are permitted. 406 * In this case, the method will return immediately without reading any 407 * bytes from the stream. 408 * 409 * @param buf The buffer into which to read the data 410 * 411 * @exception EOFException If end of file is reached before filling the 412 * buffer 413 * @exception IOException If any other error occurs 414 */ 415 void readFully(byte[] buf) throws EOFException, IOException; 416 417 /** 418 * This method reads raw bytes into the passed array <code>buf</code> 419 * starting 420 * <code>offset</code> bytes into the buffer. The number of bytes read 421 * will be 422 * exactly <code>len</code>. Note that this method blocks until the data is 423 * available and throws an exception if there is not enough data left in 424 * the stream to read <code>len</code> bytes. Note also that zero length 425 * buffers are permitted. In this case, the method will return immediately 426 * without reading any bytes from the stream. 427 * 428 * @param buf The buffer into which to read the data 429 * @param offset The offset into the buffer to start storing data 430 * @param len The number of bytes to read into the buffer 431 * 432 * @exception EOFException If end of file is reached before filling the 433 * buffer 434 * @exception IOException If any other error occurs 435 */ 436 void readFully(byte[] buf, int offset, int len) 437 throws EOFException, IOException; 438 439 /** 440 * This method skips and discards the specified number of bytes in an 441 * input stream. Note that this method may skip less than the requested 442 * number of bytes. The actual number of bytes skipped is returned. 443 * No bytes are skipped if a negative number is passed to this method. 444 * 445 * @param numBytes The number of bytes to skip 446 * 447 * @return The number of bytes actually skipped, which will always be 448 * <code>numBytes</code> 449 * 450 * @exception EOFException If end of file is reached before all bytes can be 451 * skipped 452 * @exception IOException If any other error occurs 453 */ 454 int skipBytes(int numBytes) throws EOFException, IOException; 455 456} // interface DataInput