integer.java

gcc的组建

   * code is simply its value.
   *
   * @return this Object's hash code
   */
  public int hashCode()
  {
    return value;
  }

  /**
   * Returns <code>true</code> if <code>obj</code> is an instance of
   * <code>Integer</code> and represents the same int value.
   *
   * @param obj the object to compare
   * @return whether these Objects are semantically equal
   */
  public boolean equals(Object obj)
  {
    return obj instanceof Integer && value == ((Integer) obj).value;
  }

  /**
   * Get the specified system property as an <code>Integer</code>. The
   * <code>decode()</code> method will be used to interpret the value of
   * the property.
   *
   * @param nm the name of the system property
   * @return the system property as an <code>Integer</code>, or null if the
   *         property is not found or cannot be decoded
   * @throws SecurityException if accessing the system property is forbidden
   * @see System#getProperty(String)
   * @see #decode(String)
   */
  public static Integer getInteger(String nm)
  {
    return getInteger(nm, null);
  }

  /**
   * Get the specified system property as an <code>Integer</code>, or use a
   * default <code>int</code> value if the property is not found or is not
   * decodable. The <code>decode()</code> method will be used to interpret
   * the value of the property.
   *
   * @param nm the name of the system property
   * @param val the default value
   * @return the value of the system property, or the default
   * @throws SecurityException if accessing the system property is forbidden
   * @see System#getProperty(String)
   * @see #decode(String)
   */
  public static Integer getInteger(String nm, int val)
  {
    Integer result = getInteger(nm, null);
    return result == null ? new Integer(val) : result;
  }

  /**
   * Get the specified system property as an <code>Integer</code>, or use a
   * default <code>Integer</code> value if the property is not found or is
   * not decodable. The <code>decode()</code> method will be used to
   * interpret the value of the property.
   *
   * @param nm the name of the system property
   * @param def the default value
   * @return the value of the system property, or the default
   * @throws SecurityException if accessing the system property is forbidden
   * @see System#getProperty(String)
   * @see #decode(String)
   */
  public static Integer getInteger(String nm, Integer def)
  {
    if (nm == null || "".equals(nm))
      return def;
    nm = System.getProperty(nm);
    if (nm == null)
      return def;
    try
      {
        return decode(nm);
      }
    catch (NumberFormatException e)
      {
        return def;
      }
  }

  /**
   * Convert the specified <code>String</code> into an <code>Integer</code>.
   * The <code>String</code> may represent decimal, hexadecimal, or
   * octal numbers.
   *
   * <p>The extended BNF grammar is as follows:<br>
   * <pre>
   * <em>DecodableString</em>:
   *      ( [ <code>-</code> ] <em>DecimalNumber</em> )
   *    | ( [ <code>-</code> ] ( <code>0x</code> | <code>0X</code>
   *              | <code>#</code> ) <em>HexDigit</em> { <em>HexDigit</em> } )
   *    | ( [ <code>-</code> ] <code>0</code> { <em>OctalDigit</em> } )
   * <em>DecimalNumber</em>:
   *        <em>DecimalDigit except '0'</em> { <em>DecimalDigit</em> }
   * <em>DecimalDigit</em>:
   *        <em>Character.digit(d, 10) has value 0 to 9</em>
   * <em>OctalDigit</em>:
   *        <em>Character.digit(d, 8) has value 0 to 7</em>
   * <em>DecimalDigit</em>:
   *        <em>Character.digit(d, 16) has value 0 to 15</em>
   * </pre>
   * Finally, the value must be in the range <code>MIN_VALUE</code> to
   * <code>MAX_VALUE</code>, or an exception is thrown.
   *
   * @param str the <code>String</code> to interpret
   * @return the value of the String as an <code>Integer</code>
   * @throws NumberFormatException if <code>s</code> cannot be parsed as a
   *         <code>int</code>
   * @throws NullPointerException if <code>s</code> is null
   * @since 1.2
   */
  public static Integer decode(String str)
  {
    return new Integer(parseInt(str, 10, true));
  }

  /**
   * Compare two Integers numerically by comparing their <code>int</code>
   * values. The result is positive if the first is greater, negative if the
   * second is greater, and 0 if the two are equal.
   *
   * @param i the Integer to compare
   * @return the comparison
   * @since 1.2
   */
  public int compareTo(Integer i)
  {
    if (value == i.value)
      return 0;
    // Returns just -1 or 1 on inequality; doing math might overflow.
    return value > i.value ? 1 : -1;
  }

  /**
   * Behaves like <code>compareTo(Integer)</code> unless the Object
   * is not an <code>Integer</code>.
   *
   * @param o the object to compare
   * @return the comparison
   * @throws ClassCastException if the argument is not an <code>Integer</code>
   * @see #compareTo(Integer)
   * @see Comparable
   * @since 1.2
   */
  public int compareTo(Object o)
  {
    return compareTo((Integer) o);
  }

  /**
   * Return the number of bits set in x.
   * @param x value to examine
   * @since 1.5
   */
  public static int bitCount(int x)
  {
    // Successively collapse alternating bit groups into a sum.
    x = ((x >> 1) & 0x55555555) + (x & 0x55555555);
    x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
    x = ((x >> 4) & 0x0f0f0f0f) + (x & 0x0f0f0f0f);
    x = ((x >> 8) & 0x00ff00ff) + (x & 0x00ff00ff);
    return ((x >> 16) & 0x0000ffff) + (x & 0x0000ffff);
  }

  /**
   * Rotate x to the left by distance bits.
   * @param x the value to rotate
   * @param distance the number of bits by which to rotate
   * @since 1.5
   */
  public static int rotateLeft(int x, int distance)
  {
    // This trick works because the shift operators implicitly mask
    // the shift count.
    return (x << distance) | (x >>> - distance);
  }

  /**
   * Rotate x to the right by distance bits.
   * @param x the value to rotate
   * @param distance the number of bits by which to rotate
   * @since 1.5
   */
  public static int rotateRight(int x, int distance)
  {
    // This trick works because the shift operators implicitly mask
    // the shift count.
    return (x << - distance) | (x >>> distance);
  }

  /**
   * Find the highest set bit in value, and return a new value
   * with only that bit set.
   * @param value the value to examine
   * @since 1.5
   */
  public static int highestOneBit(int value)
  {
    value |= value >>> 1;
    value |= value >>> 2;
    value |= value >>> 4;
    value |= value >>> 8;
    value |= value >>> 16;
    return value ^ (value >>> 1);
  }

  /**
   * Return the number of leading zeros in value.
   * @param value the value to examine
   * @since 1.5
   */
  public static int numberOfLeadingZeros(int value)
  {
    value |= value >>> 1;
    value |= value >>> 2;
    value |= value >>> 4;
    value |= value >>> 8;
    value |= value >>> 16;
    return bitCount(~value);
  }

  /**
   * Find the lowest set bit in value, and return a new value
   * with only that bit set.
   * @param value the value to examine
   * @since 1.5
   */
  public static int lowestOneBit(int value)
  {
    // Classic assembly trick.
    return value & - value;
  }

  /**
   * Find the number of trailing zeros in value.
   * @param value the value to examine
   * @since 1.5
   */
  public static int numberOfTrailingZeros(int value)
  {
    return bitCount((value & -value) - 1);
  }

  /**
   * Return 1 if x is positive, -1 if it is negative, and 0 if it is
   * zero.
   * @param x the value to examine
   * @since 1.5
   */
  public static int signum(int x)
  {
    return x < 0 ? -1 : (x > 0 ? 1 : 0);
  }

  /**
   * Reverse the bytes in val.
   * @since 1.5
   */
  public static int reverseBytes(int val)
  {
    return (  ((val >> 24) & 0xff)
	    | ((val >> 8) & 0xff00)
	    | ((val << 8) & 0xff0000)
	    | ((val << 24) & 0xff000000));
  }

  /**
   * Reverse the bits in val.
   * @since 1.5
   */
  public static int reverse(int val)
  {
    // Successively swap alternating bit groups.
    val = ((val >> 1) & 0x55555555) + ((val << 1) & ~0x55555555);
    val = ((val >> 2) & 0x33333333) + ((val << 2) & ~0x33333333);
    val = ((val >> 4) & 0x0f0f0f0f) + ((val << 4) & ~0x0f0f0f0f);
    val = ((val >> 8) & 0x00ff00ff) + ((val << 8) & ~0x00ff00ff);
    return ((val >> 16) & 0x0000ffff) + ((val << 16) & ~0x0000ffff);
  }

  /**
   * Helper for converting unsigned numbers to String.
   *
   * @param num the number
   * @param exp log2(digit) (ie. 1, 3, or 4 for binary, oct, hex)
   */
  // Package visible for use by Long.
  static String toUnsignedString(int num, int exp)
  {
    // Use an array large enough for a binary number.
    int mask = (1 << exp) - 1;
    char[] buffer = new char[32];
    int i = 32;
    do
      {
        buffer[--i] = digits[num & mask];
        num >>>= exp;
      }
    while (num != 0);

    // Package constructor avoids an array copy.
    return new String(buffer, i, 32 - i, true);
  }

  /**
   * Helper for parsing ints, used by Integer, Short, and Byte.
   *
   * @param str the string to parse
   * @param radix the radix to use, must be 10 if decode is true
   * @param decode if called from decode
   * @return the parsed int value
   * @throws NumberFormatException if there is an error
   * @throws NullPointerException if decode is true and str if null
   * @see #parseInt(String, int)
   * @see #decode(String)
   * @see Byte#parseByte(String, int)
   * @see Short#parseShort(String, int)
   */
  static int parseInt(String str, int radix, boolean decode)
  {
    if (! decode && str == null)
      throw new NumberFormatException();
    int index = 0;
    int len = str.length();
    boolean isNeg = false;
    if (len == 0)
      throw new NumberFormatException("string length is null");
    int ch = str.charAt(index);
    if (ch == '-')
      {
        if (len == 1)
          throw new NumberFormatException("pure '-'");
        isNeg = true;
        ch = str.charAt(++index);
      }
    if (decode)
      {
        if (ch == '0')
          {
            if (++index == len)
              return 0;
            if ((str.charAt(index) & ~('x' ^ 'X')) == 'X')
              {
                radix = 16;
                index++;
              }
            else
              radix = 8;
          }
        else if (ch == '#')
          {
            radix = 16;
            index++;
          }
      }
    if (index == len)
      throw new NumberFormatException("non terminated number: " + str);

    int max = MAX_VALUE / radix;
    // We can't directly write `max = (MAX_VALUE + 1) / radix'.
    // So instead we fake it.
    if (isNeg && MAX_VALUE % radix == radix - 1)
      ++max;

    int val = 0;
    while (index < len)
      {
	if (val < 0 || val > max)
	  throw new NumberFormatException("number overflow (pos=" + index + ") : " + str);

        ch = Character.digit(str.charAt(index++), radix);
        val = val * radix + ch;
        if (ch < 0 || (val < 0 && (! isNeg || val != MIN_VALUE)))
          throw new NumberFormatException("invalid character at position " + index + " in " + str);
      }
    return isNeg ? -val : val;
  }
}