- Byte 类字节，属于Number。
1 public final class Byte extends Number implements Comparable<Byte> { 2 3 /** 4 * A constant holding the minimum value a {@code byte} can 5 * have, -2<sup>7</sup>. 6 */ 7 public static final byte MIN_VALUE = -128; 8 9 /** 10 * A constant holding the maximum value a {@code byte} can 11 * have, 2<sup>7</sup>-1. 12 */ 13 public static final byte MAX_VALUE = 127; 14 15 /** 16 * The {@code Class} instance representing the primitive type 17 * {@code byte}. 18 */ 19 @SuppressWarnings("unchecked") 20 public static final Class<Byte> TYPE = (Class<Byte>) Class.getPrimitiveClass("byte"); 21 22 /** 23 * Returns a new {@code String} object representing the 24 * specified {@code byte}. The radix is assumed to be 10. 25 * 26 * @param b the {@code byte} to be converted 27 * @return the string representation of the specified {@code byte} 28 * @see java.lang.Integer#toString(int) 29 */ 30 public static String toString(byte b) { 31 return Integer.toString((int)b, 10); 32 } 33 34 private static class ByteCache { 35 private ByteCache(){} 36 37 static final Byte cache[] = new Byte[-(-128) + 127 + 1]; 38 39 static { 40 for(int i = 0; i < cache.length; i++) 41 cache[i] = new Byte((byte)(i - 128)); 42 } 43 } 44 45 /** 46 * Returns a {@code Byte} instance representing the specified 47 * {@code byte} value. 48 * If a new {@code Byte} instance is not required, this method 49 * should generally be used in preference to the constructor 50 * {@link #Byte(byte)}, as this method is likely to yield 51 * significantly better space and time performance since 52 * all byte values are cached. 53 * 54 * @param b a byte value. 55 * @return a {@code Byte} instance representing {@code b}. 56 * @since 1.5 57 */ 58 public static Byte valueOf(byte b) { 59 final int offset = 128; 60 return ByteCache.cache[(int)b + offset]; 61 } 62 63 /** 64 * Parses the string argument as a signed {@code byte} in the 65 * radix specified by the second argument. The characters in the 66 * string must all be digits, of the specified radix (as 67 * determined by whether {@link java.lang.Character#digit(char, 68 * int)} returns a nonnegative value) except that the first 69 * character may be an ASCII minus sign {@code ‘-‘} 70 * ({@code ‘\u005Cu002D‘}) to indicate a negative value or an 71 * ASCII plus sign {@code ‘+‘} ({@code ‘\u005Cu002B‘}) to 72 * indicate a positive value. The resulting {@code byte} value is 73 * returned. 74 * 75 * <p>An exception of type {@code NumberFormatException} is 76 * thrown if any of the following situations occurs: 77 * <ul> 78 * <li> The first argument is {@code null} or is a string of 79 * length zero. 80 * 81 * <li> The radix is either smaller than {@link 82 * java.lang.Character#MIN_RADIX} or larger than {@link 83 * java.lang.Character#MAX_RADIX}. 84 * 85 * <li> Any character of the string is not a digit of the 86 * specified radix, except that the first character may be a minus 87 * sign {@code ‘-‘} ({@code ‘\u005Cu002D‘}) or plus sign 88 * {@code ‘+‘} ({@code ‘\u005Cu002B‘}) provided that the 89 * string is longer than length 1. 90 * 91 * <li> The value represented by the string is not a value of type 92 * {@code byte}. 93 * </ul> 94 * 95 * @param s the {@code String} containing the 96 * {@code byte} 97 * representation to be parsed 98 * @param radix the radix to be used while parsing {@code s} 99 * @return the {@code byte} value represented by the string 100 * argument in the specified radix 101 * @throws NumberFormatException If the string does 102 * not contain a parsable {@code byte}. 103 */ 104 public static byte parseByte(String s, int radix) 105 throws NumberFormatException { 106 int i = Integer.parseInt(s, radix); 107 if (i < MIN_VALUE || i > MAX_VALUE) 108 throw new NumberFormatException( 109 "Value out of range. Value:\"" + s + "\" Radix:" + radix); 110 return (byte)i; 111 } 112 113 /** 114 * Parses the string argument as a signed decimal {@code 115 * byte}. The characters in the string must all be decimal digits, 116 * except that the first character may be an ASCII minus sign 117 * {@code ‘-‘} ({@code ‘\u005Cu002D‘}) to indicate a negative 118 * value or an ASCII plus sign {@code ‘+‘} 119 * ({@code ‘\u005Cu002B‘}) to indicate a positive value. The 120 * resulting {@code byte} value is returned, exactly as if the 121 * argument and the radix 10 were given as arguments to the {@link 122 * #parseByte(java.lang.String, int)} method. 123 * 124 * @param s a {@code String} containing the 125 * {@code byte} representation to be parsed 126 * @return the {@code byte} value represented by the 127 * argument in decimal 128 * @throws NumberFormatException if the string does not 129 * contain a parsable {@code byte}. 130 */ 131 public static byte parseByte(String s) throws NumberFormatException { 132 return parseByte(s, 10); 133 } 134 135 /** 136 * Returns a {@code Byte} object holding the value 137 * extracted from the specified {@code String} when parsed 138 * with the radix given by the second argument. The first argument 139 * is interpreted as representing a signed {@code byte} in 140 * the radix specified by the second argument, exactly as if the 141 * argument were given to the {@link #parseByte(java.lang.String, 142 * int)} method. The result is a {@code Byte} object that 143 * represents the {@code byte} value specified by the string. 144 * 145 * <p> In other words, this method returns a {@code Byte} object 146 * equal to the value of: 147 * 148 * <blockquote> 149 * {@code new Byte(Byte.parseByte(s, radix))} 150 * </blockquote> 151 * 152 * @param s the string to be parsed 153 * @param radix the radix to be used in interpreting {@code s} 154 * @return a {@code Byte} object holding the value 155 * represented by the string argument in the 156 * specified radix. 157 * @throws NumberFormatException If the {@code String} does 158 * not contain a parsable {@code byte}. 159 */ 160 public static Byte valueOf(String s, int radix) 161 throws NumberFormatException { 162 return valueOf(parseByte(s, radix)); 163 } 164 165 /** 166 * Returns a {@code Byte} object holding the value 167 * given by the specified {@code String}. The argument is 168 * interpreted as representing a signed decimal {@code byte}, 169 * exactly as if the argument were given to the {@link 170 * #parseByte(java.lang.String)} method. The result is a 171 * {@code Byte} object that represents the {@code byte} 172 * value specified by the string. 173 * 174 * <p> In other words, this method returns a {@code Byte} object 175 * equal to the value of: 176 * 177 * <blockquote> 178 * {@code new Byte(Byte.parseByte(s))} 179 * </blockquote> 180 * 181 * @param s the string to be parsed 182 * @return a {@code Byte} object holding the value 183 * represented by the string argument 184 * @throws NumberFormatException If the {@code String} does 185 * not contain a parsable {@code byte}. 186 */ 187 public static Byte valueOf(String s) throws NumberFormatException { 188 return valueOf(s, 10); 189 } 190 191 /** 192 * Decodes a {@code String} into a {@code Byte}. 193 * Accepts decimal, hexadecimal, and octal numbers given by 194 * the following grammar: 195 * 196 * <blockquote> 197 * <dl> 198 * <dt><i>DecodableString:</i> 199 * <dd><i>Sign<sub>opt</sub> DecimalNumeral</i> 200 * <dd><i>Sign<sub>opt</sub></i> {@code 0x} <i>HexDigits</i> 201 * <dd><i>Sign<sub>opt</sub></i> {@code 0X} <i>HexDigits</i> 202 * <dd><i>Sign<sub>opt</sub></i> {@code #} <i>HexDigits</i> 203 * <dd><i>Sign<sub>opt</sub></i> {@code 0} <i>OctalDigits</i> 204 * 205 * <dt><i>Sign:</i> 206 * <dd>{@code -} 207 * <dd>{@code +} 208 * </dl> 209 * </blockquote> 210 * 211 * <i>DecimalNumeral</i>, <i>HexDigits</i>, and <i>OctalDigits</i> 212 * are as defined in section 3.10.1 of 213 * <cite>The Java™ Language Specification</cite>, 214 * except that underscores are not accepted between digits. 215 * 216 * <p>The sequence of characters following an optional 217 * sign and/or radix specifier ("{@code 0x}", "{@code 0X}", 218 * "{@code #}", or leading zero) is parsed as by the {@code 219 * Byte.parseByte} method with the indicated radix (10, 16, or 8). 220 * This sequence of characters must represent a positive value or 221 * a {@link NumberFormatException} will be thrown. The result is 222 * negated if first character of the specified {@code String} is 223 * the minus sign. No whitespace characters are permitted in the 224 * {@code String}. 225 * 226 * @param nm the {@code String} to decode. 227 * @return a {@code Byte} object holding the {@code byte} 228 * value represented by {@code nm} 229 * @throws NumberFormatException if the {@code String} does not 230 * contain a parsable {@code byte}. 231 * @see java.lang.Byte#parseByte(java.lang.String, int) 232 */ 233 public static Byte decode(String nm) throws NumberFormatException { 234 int i = Integer.decode(nm); 235 if (i < MIN_VALUE || i > MAX_VALUE) 236 throw new NumberFormatException( 237 "Value " + i + " out of range from input " + nm); 238 return valueOf((byte)i); 239 } 240 241 /** 242 * The value of the {@code Byte}. 243 * 244 * @serial 245 */ 246 private final byte value; 247 248 /** 249 * Constructs a newly allocated {@code Byte} object that 250 * represents the specified {@code byte} value. 251 * 252 * @param value the value to be represented by the 253 * {@code Byte}. 254 */ 255 public Byte(byte value) { 256 this.value = value; 257 } 258 259 /** 260 * Constructs a newly allocated {@code Byte} object that 261 * represents the {@code byte} value indicated by the 262 * {@code String} parameter. The string is converted to a 263 * {@code byte} value in exactly the manner used by the 264 * {@code parseByte} method for radix 10. 265 * 266 * @param s the {@code String} to be converted to a 267 * {@code Byte} 268 * @throws NumberFormatException If the {@code String} 269 * does not contain a parsable {@code byte}. 270 * @see java.lang.Byte#parseByte(java.lang.String, int) 271 */ 272 public Byte(String s) throws NumberFormatException { 273 this.value = parseByte(s, 10); 274 } 275 276 /** 277 * Returns the value of this {@code Byte} as a 278 * {@code byte}. 279 */ 280 public byte byteValue() { 281 return value; 282 } 283 284 /** 285 * Returns the value of this {@code Byte} as a {@code short} after 286 * a widening primitive conversion. 287 * @jls 5.1.2 Widening Primitive Conversions 288 */ 289 public short shortValue() { 290 return (short)value; 291 } 292 293 /** 294 * Returns the value of this {@code Byte} as an {@code int} after 295 * a widening primitive conversion. 296 * @jls 5.1.2 Widening Primitive Conversions 297 */ 298 public int intValue() { 299 return (int)value; 300 } 301 302 /** 303 * Returns the value of this {@code Byte} as a {@code long} after 304 * a widening primitive conversion. 305 * @jls 5.1.2 Widening Primitive Conversions 306 */ 307 public long longValue() { 308 return (long)value; 309 } 310 311 /** 312 * Returns the value of this {@code Byte} as a {@code float} after 313 * a widening primitive conversion. 314 * @jls 5.1.2 Widening Primitive Conversions 315 */ 316 public float floatValue() { 317 return (float)value; 318 } 319 320 /** 321 * Returns the value of this {@code Byte} as a {@code double} 322 * after a widening primitive conversion. 323 * @jls 5.1.2 Widening Primitive Conversions 324 */ 325 public double doubleValue() { 326 return (double)value; 327 } 328 329 /** 330 * Returns a {@code String} object representing this 331 * {@code Byte}‘s value. The value is converted to signed 332 * decimal representation and returned as a string, exactly as if 333 * the {@code byte} value were given as an argument to the 334 * {@link java.lang.Byte#toString(byte)} method. 335 * 336 * @return a string representation of the value of this object in 337 * base 10. 338 */ 339 public String toString() { 340 return Integer.toString((int)value); 341 } 342 343 /** 344 * Returns a hash code for this {@code Byte}; equal to the result 345 * of invoking {@code intValue()}. 346 * 347 * @return a hash code value for this {@code Byte} 348 */ 349 @Override 350 public int hashCode() { 351 return Byte.hashCode(value); 352 } 353 354 /** 355 * Returns a hash code for a {@code byte} value; compatible with 356 * {@code Byte.hashCode()}. 357 * 358 * @param value the value to hash 359 * @return a hash code value for a {@code byte} value. 360 * @since 1.8 361 */ 362 public static int hashCode(byte value) { 363 return (int)value; 364 } 365 366 /** 367 * Compares this object to the specified object. The result is 368 * {@code true} if and only if the argument is not 369 * {@code null} and is a {@code Byte} object that 370 * contains the same {@code byte} value as this object. 371 * 372 * @param obj the object to compare with 373 * @return {@code true} if the objects are the same; 374 * {@code false} otherwise. 375 */ 376 public boolean equals(Object obj) { 377 if (obj instanceof Byte) { 378 return value == ((Byte)obj).byteValue(); 379 } 380 return false; 381 } 382 383 /** 384 * Compares two {@code Byte} objects numerically. 385 * 386 * @param anotherByte the {@code Byte} to be compared. 387 * @return the value {@code 0} if this {@code Byte} is 388 * equal to the argument {@code Byte}; a value less than 389 * {@code 0} if this {@code Byte} is numerically less 390 * than the argument {@code Byte}; and a value greater than 391 * {@code 0} if this {@code Byte} is numerically 392 * greater than the argument {@code Byte} (signed 393 * comparison). 394 * @since 1.2 395 */ 396 public int compareTo(Byte anotherByte) { 397 return compare(this.value, anotherByte.value); 398 } 399 400 /** 401 * Compares two {@code byte} values numerically. 402 * The value returned is identical to what would be returned by: 403 * <pre> 404 * Byte.valueOf(x).compareTo(Byte.valueOf(y)) 405 * </pre> 406 * 407 * @param x the first {@code byte} to compare 408 * @param y the second {@code byte} to compare 409 * @return the value {@code 0} if {@code x == y}; 410 * a value less than {@code 0} if {@code x < y}; and 411 * a value greater than {@code 0} if {@code x > y} 412 * @since 1.7 413 */ 414 public static int compare(byte x, byte y) { 415 return x - y; 416 } 417 418 /** 419 * Converts the argument to an {@code int} by an unsigned 420 * conversion. In an unsigned conversion to an {@code int}, the 421 * high-order 24 bits of the {@code int} are zero and the 422 * low-order 8 bits are equal to the bits of the {@code byte} argument. 423 * 424 * Consequently, zero and positive {@code byte} values are mapped 425 * to a numerically equal {@code int} value and negative {@code 426 * byte} values are mapped to an {@code int} value equal to the 427 * input plus 2<sup>8</sup>. 428 * 429 * @param x the value to convert to an unsigned {@code int} 430 * @return the argument converted to {@code int} by an unsigned 431 * conversion 432 * @since 1.8 433 */ 434 public static int toUnsignedInt(byte x) { 435 return ((int) x) & 0xff; 436 } 437 438 /** 439 * Converts the argument to a {@code long} by an unsigned 440 * conversion. In an unsigned conversion to a {@code long}, the 441 * high-order 56 bits of the {@code long} are zero and the 442 * low-order 8 bits are equal to the bits of the {@code byte} argument. 443 * 444 * Consequently, zero and positive {@code byte} values are mapped 445 * to a numerically equal {@code long} value and negative {@code 446 * byte} values are mapped to a {@code long} value equal to the 447 * input plus 2<sup>8</sup>. 448 * 449 * @param x the value to convert to an unsigned {@code long} 450 * @return the argument converted to {@code long} by an unsigned 451 * conversion 452 * @since 1.8 453 */ 454 public static long toUnsignedLong(byte x) { 455 return ((long) x) & 0xffL; 456 } 457 458 459 /** 460 * The number of bits used to represent a {@code byte} value in two‘s 461 * complement binary form. 462 * 463 * @since 1.5 464 */ 465 public static final int SIZE = 8; 466 467 /** 468 * The number of bytes used to represent a {@code byte} value in two‘s 469 * complement binary form. 470 * 471 * @since 1.8 472 */ 473 public static final int BYTES = SIZE / Byte.SIZE; 474 475 /** use serialVersionUID from JDK 1.1. for interoperability */ 476 private static final long serialVersionUID = -7183698231559129828L; 477 }
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