libjava/java/io/DataInput.java

   1 /* DataInput.java -- Interface for reading data from a stream
   2    Copyright (C) 1998, 1999, 2001, 2003, 2005  Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.io;
  40
  41 /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
  42  * "The Java Language Specification", ISBN 0-201-63451-1
  43  * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
  44  * Status:  Believed complete and correct.  */
  45
  46 /**
  47  * This interface is implemented by classes that can data from streams
  48  * into Java primitive types.
  49  *
  50  * @author Aaron M. Renn (arenn@urbanophile.com)
  51  * @author Warren Levy (warrenl@cygnus.com)
  52  */
  53 public interface DataInput
  54 {
  55
  56   /**
  57    * This method reads a Java boolean value from an input stream.  It does
  58    * so by reading a single byte of data.  If that byte is zero, then the
  59    * value returned is <code>false</code>.  If the byte is non-zero, then
  60    * the value returned is <code>true</code>.
  61    * <p>
  62    * This method can read a <code>boolean</code> written by an object
  63    * implementing the <code>writeBoolean()</code> method in the
  64    * <code>DataOutput</code> interface.
  65    *
  66    * @return The <code>boolean</code> value read
  67    *
  68    * @exception EOFException If end of file is reached before
  69    * reading the boolean
  70    * @exception IOException If any other error occurs
  71    *
  72    * @see DataOutput#writeBoolean
  73    */
  74   boolean readBoolean() throws EOFException, IOException;
  75
  76   /**
  77    * This method reads a Java byte value from an input stream.  The value
  78    * is in the range of -128 to 127.
  79    * <p>
  80    * This method can read a <code>byte</code> written by an object
  81    * implementing the
  82    * <code>writeByte()</code> method in the <code>DataOutput</code> interface.
  83    * <p>
  84    * @return The <code>byte</code> value read
  85    *
  86    * @exception EOFException If end of file is reached before reading the byte
  87    * @exception IOException If any other error occurs
  88    *
  89    * @see DataOutput#writeByte
  90    */
  91   byte readByte() throws EOFException, IOException;
  92
  93   /**
  94    * This method reads 8 unsigned bits into a Java <code>int</code> value from
  95    * the stream. The value returned is in the range of 0 to 255.
  96    * <p>
  97    * This method can read an unsigned byte written by an object
  98    * implementing the
  99    * <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 &amp; 0x1F) &lt;&lt; 6) + (byte2 &amp; 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 &amp; 0x0F) &lt;&lt; 12) + ((byte2 &amp; 0x3F) + (byte3 &amp; 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>\&lt;llll&gt;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