java.lang.Byte 类源码浅析

• Byte 类字节，属于Number。

   public final class Byte extends Number implements Comparable<Byte> {
  
       /**
        * A constant holding the minimum value a {@code byte} can
        * have, -2<sup>7</sup>.
        */
       public static final byte   MIN_VALUE = -128;
  
       /**
        * A constant holding the maximum value a {@code byte} can
        * have, 2<sup>7</sup>-1.
        */
       public static final byte   MAX_VALUE = 127;
  
       /**
        * The {@code Class} instance representing the primitive type
        * {@code byte}.
        */
       @SuppressWarnings("unchecked")
       public static final Class<Byte>     TYPE = (Class<Byte>) Class.getPrimitiveClass("byte");
  
       /**
        * Returns a new {@code String} object representing the
        * specified {@code byte}. The radix is assumed to be 10.
        *
        * @param b the {@code byte} to be converted
        * @return the string representation of the specified {@code byte}
        * @see java.lang.Integer#toString(int)
        */
       public static String toString(byte b) {
           return Integer.toString((int)b, 10);
       }
  
       private static class ByteCache {
           private ByteCache(){}
  
           static final Byte cache[] = new Byte[-(-128) + 127 + 1];
  
           static {
               for(int i = 0; i < cache.length; i++)
                   cache[i] = new Byte((byte)(i - 128));
           }
       }
  
       /**
        * Returns a {@code Byte} instance representing the specified
        * {@code byte} value.
        * If a new {@code Byte} instance is not required, this method
        * should generally be used in preference to the constructor
        * {@link #Byte(byte)}, as this method is likely to yield
        * significantly better space and time performance since
        * all byte values are cached.
        *
        * @param  b a byte value.
        * @return a {@code Byte} instance representing {@code b}.
        * @since  1.5
        */
       public static Byte valueOf(byte b) {
           final int offset = 128;
           return ByteCache.cache[(int)b + offset];
       }
  
       /**
        * Parses the string argument as a signed {@code byte} in the
        * radix specified by the second argument. The characters in the
        * string must all be digits, of the specified radix (as
        * determined by whether {@link java.lang.Character#digit(char,
        * int)} returns a nonnegative value) except that the first
        * character may be an ASCII minus sign {@code '-'}
        * ({@code '\u005Cu002D'}) to indicate a negative value or an
        * ASCII plus sign {@code '+'} ({@code '\u005Cu002B'}) to
        * indicate a positive value.  The resulting {@code byte} value is
        * returned.
        *
        * <p>An exception of type {@code NumberFormatException} is
        * thrown if any of the following situations occurs:
        * <ul>
        * <li> The first argument is {@code null} or is a string of
        * length zero.
        *
        * <li> The radix is either smaller than {@link
        * java.lang.Character#MIN_RADIX} or larger than {@link
        * java.lang.Character#MAX_RADIX}.
        *
        * <li> Any character of the string is not a digit of the
        * specified radix, except that the first character may be a minus
        * sign {@code '-'} ({@code '\u005Cu002D'}) or plus sign
        * {@code '+'} ({@code '\u005Cu002B'}) provided that the
        * string is longer than length 1.
        *
        * <li> The value represented by the string is not a value of type
        * {@code byte}.
        * </ul>
        *
        * @param s         the {@code String} containing the
        *                  {@code byte}
        *                  representation to be parsed
        * @param radix     the radix to be used while parsing {@code s}
        * @return          the {@code byte} value represented by the string
        *                   argument in the specified radix
        * @throws          NumberFormatException If the string does
        *                  not contain a parsable {@code byte}.
        */
       public static byte parseByte(String s, int radix)
           throws NumberFormatException {
           int i = Integer.parseInt(s, radix);
           if (i < MIN_VALUE || i > MAX_VALUE)
               throw new NumberFormatException(
                   "Value out of range. Value:\"" + s + "\" Radix:" + radix);
           return (byte)i;
       }
  
       /**
        * Parses the string argument as a signed decimal {@code
        * byte}. The characters in the string must all be decimal digits,
        * except that the first character may be an ASCII minus sign
        * {@code '-'} ({@code '\u005Cu002D'}) to indicate a negative
        * value or an ASCII plus sign {@code '+'}
        * ({@code '\u005Cu002B'}) to indicate a positive value. The
        * resulting {@code byte} value is returned, exactly as if the
        * argument and the radix 10 were given as arguments to the {@link
        * #parseByte(java.lang.String, int)} method.
        *
        * @param s         a {@code String} containing the
        *                  {@code byte} representation to be parsed
        * @return          the {@code byte} value represented by the
        *                  argument in decimal
        * @throws          NumberFormatException if the string does not
        *                  contain a parsable {@code byte}.
        */
       public static byte parseByte(String s) throws NumberFormatException {
           return parseByte(s, 10);
       }
  
       /**
        * Returns a {@code Byte} object holding the value
        * extracted from the specified {@code String} when parsed
        * with the radix given by the second argument. The first argument
        * is interpreted as representing a signed {@code byte} in
        * the radix specified by the second argument, exactly as if the
        * argument were given to the {@link #parseByte(java.lang.String,
        * int)} method. The result is a {@code Byte} object that
        * represents the {@code byte} value specified by the string.
        *
        * <p> In other words, this method returns a {@code Byte} object
        * equal to the value of:
        *
        * <blockquote>
        * {@code new Byte(Byte.parseByte(s, radix))}
        * </blockquote>
        *
        * @param s         the string to be parsed
        * @param radix     the radix to be used in interpreting {@code s}
        * @return          a {@code Byte} object holding the value
        *                  represented by the string argument in the
        *                  specified radix.
        * @throws          NumberFormatException If the {@code String} does
        *                  not contain a parsable {@code byte}.
        */
       public static Byte valueOf(String s, int radix)
           throws NumberFormatException {
           return valueOf(parseByte(s, radix));
       }
  
       /**
        * Returns a {@code Byte} object holding the value
        * given by the specified {@code String}. The argument is
        * interpreted as representing a signed decimal {@code byte},
        * exactly as if the argument were given to the {@link
        * #parseByte(java.lang.String)} method. The result is a
        * {@code Byte} object that represents the {@code byte}
        * value specified by the string.
        *
        * <p> In other words, this method returns a {@code Byte} object
        * equal to the value of:
        *
        * <blockquote>
        * {@code new Byte(Byte.parseByte(s))}
        * </blockquote>
        *
        * @param s         the string to be parsed
        * @return          a {@code Byte} object holding the value
        *                  represented by the string argument
        * @throws          NumberFormatException If the {@code String} does
        *                  not contain a parsable {@code byte}.
        */
       public static Byte valueOf(String s) throws NumberFormatException {
           return valueOf(s, 10);
       }
  
       /**
        * Decodes a {@code String} into a {@code Byte}.
        * Accepts decimal, hexadecimal, and octal numbers given by
        * the following grammar:
        *
        * <blockquote>
        * <dl>
        * <dt><i>DecodableString:</i>
        * <dd><i>Sign<sub>opt</sub> DecimalNumeral</i>
        * <dd><i>Sign<sub>opt</sub></i> {@code 0x} <i>HexDigits</i>
        * <dd><i>Sign<sub>opt</sub></i> {@code 0X} <i>HexDigits</i>
        * <dd><i>Sign<sub>opt</sub></i> {@code #} <i>HexDigits</i>
        * <dd><i>Sign<sub>opt</sub></i> {@code 0} <i>OctalDigits</i>
        *
        * <dt><i>Sign:</i>
        * <dd>{@code -}
        * <dd>{@code +}
        * </dl>
        * </blockquote>
        *
        * <i>DecimalNumeral</i>, <i>HexDigits</i>, and <i>OctalDigits</i>
        * are as defined in section 3.10.1 of
        * <cite>The Java&trade; Language Specification</cite>,
        * except that underscores are not accepted between digits.
        *
        * <p>The sequence of characters following an optional
        * sign and/or radix specifier ("{@code 0x}", "{@code 0X}",
        * "{@code #}", or leading zero) is parsed as by the {@code
        * Byte.parseByte} method with the indicated radix (10, 16, or 8).
        * This sequence of characters must represent a positive value or
        * a {@link NumberFormatException} will be thrown.  The result is
        * negated if first character of the specified {@code String} is
        * the minus sign.  No whitespace characters are permitted in the
        * {@code String}.
        *
        * @param     nm the {@code String} to decode.
        * @return   a {@code Byte} object holding the {@code byte}
        *          value represented by {@code nm}
        * @throws  NumberFormatException  if the {@code String} does not
        *            contain a parsable {@code byte}.
        * @see java.lang.Byte#parseByte(java.lang.String, int)
        */
       public static Byte decode(String nm) throws NumberFormatException {
           int i = Integer.decode(nm);
           if (i < MIN_VALUE || i > MAX_VALUE)
               throw new NumberFormatException(
                       "Value " + i + " out of range from input " + nm);
           return valueOf((byte)i);
       }
  
       /**
        * The value of the {@code Byte}.
        *
        * @serial
        */
       private final byte value;
  
       /**
        * Constructs a newly allocated {@code Byte} object that
        * represents the specified {@code byte} value.
        *
        * @param value     the value to be represented by the
        *                  {@code Byte}.
        */
       public Byte(byte value) {
           this.value = value;
       }
  
       /**
        * Constructs a newly allocated {@code Byte} object that
        * represents the {@code byte} value indicated by the
        * {@code String} parameter. The string is converted to a
        * {@code byte} value in exactly the manner used by the
        * {@code parseByte} method for radix 10.
        *
        * @param s         the {@code String} to be converted to a
        *                  {@code Byte}
        * @throws           NumberFormatException If the {@code String}
        *                  does not contain a parsable {@code byte}.
        * @see        java.lang.Byte#parseByte(java.lang.String, int)
        */
       public Byte(String s) throws NumberFormatException {
           this.value = parseByte(s, 10);
       }
  
       /**
        * Returns the value of this {@code Byte} as a
        * {@code byte}.
        */
       public byte byteValue() {
           return value;
       }
  
       /**
        * Returns the value of this {@code Byte} as a {@code short} after
        * a widening primitive conversion.
        * @jls 5.1.2 Widening Primitive Conversions
        */
       public short shortValue() {
           return (short)value;
       }
  
       /**
        * Returns the value of this {@code Byte} as an {@code int} after
        * a widening primitive conversion.
        * @jls 5.1.2 Widening Primitive Conversions
        */
       public int intValue() {
           return (int)value;
       }
  
       /**
        * Returns the value of this {@code Byte} as a {@code long} after
        * a widening primitive conversion.
        * @jls 5.1.2 Widening Primitive Conversions
        */
       public long longValue() {
           return (long)value;
       }
  
       /**
        * Returns the value of this {@code Byte} as a {@code float} after
        * a widening primitive conversion.
        * @jls 5.1.2 Widening Primitive Conversions
        */
       public float floatValue() {
           return (float)value;
       }
  
       /**
        * Returns the value of this {@code Byte} as a {@code double}
        * after a widening primitive conversion.
        * @jls 5.1.2 Widening Primitive Conversions
        */
       public double doubleValue() {
           return (double)value;
       }
  
       /**
        * Returns a {@code String} object representing this
        * {@code Byte}'s value.  The value is converted to signed
        * decimal representation and returned as a string, exactly as if
        * the {@code byte} value were given as an argument to the
        * {@link java.lang.Byte#toString(byte)} method.
        *
        * @return  a string representation of the value of this object in
        *          base&nbsp;10.
        */
       public String toString() {
           return Integer.toString((int)value);
       }
  
       /**
        * Returns a hash code for this {@code Byte}; equal to the result
        * of invoking {@code intValue()}.
        *
        * @return a hash code value for this {@code Byte}
        */
       @Override
       public int hashCode() {
           return Byte.hashCode(value);
       }
  
       /**
        * Returns a hash code for a {@code byte} value; compatible with
        * {@code Byte.hashCode()}.
        *
        * @param value the value to hash
        * @return a hash code value for a {@code byte} value.
        * @since 1.8
        */
       public static int hashCode(byte value) {
           return (int)value;
       }
  
       /**
        * Compares this object to the specified object.  The result is
        * {@code true} if and only if the argument is not
        * {@code null} and is a {@code Byte} object that
        * contains the same {@code byte} value as this object.
        *
        * @param obj       the object to compare with
        * @return          {@code true} if the objects are the same;
        *                  {@code false} otherwise.
        */
       public boolean equals(Object obj) {
           if (obj instanceof Byte) {
               return value == ((Byte)obj).byteValue();
           }
           return false;
       }
  
       /**
        * Compares two {@code Byte} objects numerically.
        *
        * @param   anotherByte   the {@code Byte} to be compared.
        * @return  the value {@code 0} if this {@code Byte} is
        *          equal to the argument {@code Byte}; a value less than
        *          {@code 0} if this {@code Byte} is numerically less
        *          than the argument {@code Byte}; and a value greater than
        *           {@code 0} if this {@code Byte} is numerically
        *           greater than the argument {@code Byte} (signed
        *           comparison).
        * @since   1.2
        */
       public int compareTo(Byte anotherByte) {
           return compare(this.value, anotherByte.value);
       }
  
       /**
        * Compares two {@code byte} values numerically.
        * The value returned is identical to what would be returned by:
        * <pre>
        *    Byte.valueOf(x).compareTo(Byte.valueOf(y))
        * </pre>
        *
        * @param  x the first {@code byte} to compare
        * @param  y the second {@code byte} to compare
        * @return the value {@code 0} if {@code x == y};
        *         a value less than {@code 0} if {@code x < y}; and
        *         a value greater than {@code 0} if {@code x > y}
        * @since 1.7
        */
       public static int compare(byte x, byte y) {
           return x - y;
       }
  
       /**
        * Converts the argument to an {@code int} by an unsigned
        * conversion.  In an unsigned conversion to an {@code int}, the
        * high-order 24 bits of the {@code int} are zero and the
        * low-order 8 bits are equal to the bits of the {@code byte} argument.
        *
        * Consequently, zero and positive {@code byte} values are mapped
        * to a numerically equal {@code int} value and negative {@code
        * byte} values are mapped to an {@code int} value equal to the
        * input plus 2<sup>8</sup>.
        *
        * @param  x the value to convert to an unsigned {@code int}
        * @return the argument converted to {@code int} by an unsigned
        *         conversion
        * @since 1.8
        */
       public static int toUnsignedInt(byte x) {
           return ((int) x) & 0xff;
       }
  
       /**
        * Converts the argument to a {@code long} by an unsigned
        * conversion.  In an unsigned conversion to a {@code long}, the
        * high-order 56 bits of the {@code long} are zero and the
        * low-order 8 bits are equal to the bits of the {@code byte} argument.
        *
        * Consequently, zero and positive {@code byte} values are mapped
        * to a numerically equal {@code long} value and negative {@code
        * byte} values are mapped to a {@code long} value equal to the
        * input plus 2<sup>8</sup>.
        *
        * @param  x the value to convert to an unsigned {@code long}
        * @return the argument converted to {@code long} by an unsigned
        *         conversion
        * @since 1.8
        */
       public static long toUnsignedLong(byte x) {
           return ((long) x) & 0xffL;
       }
  
       /**
        * The number of bits used to represent a {@code byte} value in two's
        * complement binary form.
        *
        * @since 1.5
        */
       public static final int SIZE = 8;
  
       /**
        * The number of bytes used to represent a {@code byte} value in two's
        * complement binary form.
        *
        * @since 1.8
        */
       public static final int BYTES = SIZE / Byte.SIZE;
  
       /** use serialVersionUID from JDK 1.1. for interoperability */
       private static final long serialVersionUID = -7183698231559129828L;
   }