integer.java

《透视Java》的源码

        int q, r;
        int charPos = 12;
        char sign = 0;

        if (i < 0) { 
            sign = '-';
            i = -i;
        }

        // Generate two digits per iteration
        while (i >= 65536) {
            q = i / 100;
        // really: r = i - (q * 100);
            r = i - ((q << 6) + (q << 5) + (q << 2));
            i = q;
            buf [--charPos] = DigitOnes[r];
            buf [--charPos] = DigitTens[r];
        }

        // Fall thru to fast mode for smaller numbers
        // assert(i <= 65536, i);
        for (;;) { 
            q = (i * 52429) >>> (16+3);
            r = i - ((q << 3) + (q << 1));  // r = i-(q*10) ...
            buf [--charPos] = digits [r];
            i = q;
            if (i == 0) break;
        }
        if (sign != 0) {
            buf [--charPos] = sign;
        }
        return charPos;
    }
 
    static void appendTo(int i, StringBuffer sb) {
        switch(i) {
            case Integer.MIN_VALUE:
                sb.append("-2147483648");
                return;
            case -3: sb.append("-3"); return;
            case -2: sb.append("-2"); return;
            case -1: sb.append("-1"); return;
            case 0: sb.append("0"); return;
            case 1: sb.append("1"); return;
            case 2: sb.append("2"); return;
            case 3: sb.append("3"); return;
            case 4: sb.append("4"); return;
            case 5: sb.append("5"); return;
            case 6: sb.append("6"); return;
            case 7: sb.append("7"); return;
            case 8: sb.append("8"); return;
            case 9: sb.append("9"); return;
            case 10: sb.append("10"); return;
        }
        char[] buf = (char[])(perThreadBuffer.get());
        int charPos = getChars(i, buf);
        sb.append(buf, charPos, 12 - charPos);
    }
    
    /**
     * Parses the string argument as a signed integer 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> (<code>'&#92;u002D'</code>) to 
     * indicate a negative value. The resulting integer value is returned. 
     * <p>
     * An exception of type <code>NumberFormatException</code> is
     * thrown if any of the following situations occurs:
     * <ul>
     * <li>The first argument is <code>null</code> 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> (<code>'&#92;u002D'</code>) provided that the
     * string is longer than length 1.
     * <li>The value represented by the string is not a value of type
     * <code>int</code>. 
     * </ul><p>
     * Examples:
     * <blockquote><pre>
     * parseInt("0", 10) returns 0
     * parseInt("473", 10) returns 473
     * parseInt("-0", 10) returns 0
     * parseInt("-FF", 16) returns -255
     * parseInt("1100110", 2) returns 102
     * parseInt("2147483647", 10) returns 2147483647
     * parseInt("-2147483648", 10) returns -2147483648
     * parseInt("2147483648", 10) throws a NumberFormatException
     * parseInt("99", 8) throws a NumberFormatException
     * parseInt("Kona", 10) throws a NumberFormatException
     * parseInt("Kona", 27) returns 411787
     * </pre></blockquote>
     *
     * @param      s   the <code>String</code> containing the integer 
     * 			representation to be parsed
     * @param      radix   the radix to be used while parsing <code>s</code>.
     * @return     the integer represented by the string argument in the
     *             specified radix.
     * @exception  NumberFormatException if the <code>String</code>
     * 		   does not contain a parsable <code>int</code>.
     */
    public static int parseInt(String s, int radix)
		throws NumberFormatException
    {
        if (s == null) {
            throw new NumberFormatException("null");
        }

	if (radix < Character.MIN_RADIX) {
	    throw new NumberFormatException("radix " + radix +
					    " less than Character.MIN_RADIX");
	}

	if (radix > Character.MAX_RADIX) {
	    throw new NumberFormatException("radix " + radix +
					    " greater than Character.MAX_RADIX");
	}

	int result = 0;
	boolean negative = false;
	int i = 0, max = s.length();
	int limit;
	int multmin;
	int digit;

	if (max > 0) {
	    if (s.charAt(0) == '-') {
		negative = true;
		limit = Integer.MIN_VALUE;
		i++;
	    } else {
		limit = -Integer.MAX_VALUE;
	    }
	    multmin = limit / radix;
	    if (i < max) {
		digit = Character.digit(s.charAt(i++),radix);
		if (digit < 0) {
		    throw NumberFormatException.forInputString(s);
		} else {
		    result = -digit;
		}
	    }
	    while (i < max) {
		// Accumulating negatively avoids surprises near MAX_VALUE
		digit = Character.digit(s.charAt(i++),radix);
		if (digit < 0) {
		    throw NumberFormatException.forInputString(s);
		}
		if (result < multmin) {
		    throw NumberFormatException.forInputString(s);
		}
		result *= radix;
		if (result < limit + digit) {
		    throw NumberFormatException.forInputString(s);
		}
		result -= digit;
	    }
	} else {
	    throw NumberFormatException.forInputString(s);
	}
	if (negative) {
	    if (i > 1) {
		return result;
	    } else {	/* Only got "-" */
		throw NumberFormatException.forInputString(s);
	    }
	} else {
	    return -result;
	}
    }

    /**
     * Parses the string argument as a signed decimal integer. The 
     * characters in the string must all be decimal digits, except that 
     * the first character may be an ASCII minus sign <code>'-'</code> 
     * (<code>'&#92;u002D'</code>) to indicate a negative value. The resulting 
     * integer value is returned, exactly as if the argument and the radix 
     * 10 were given as arguments to the 
     * {@link #parseInt(java.lang.String, int)} method.
     *
     * @param s	   a <code>String</code> containing the <code>int</code>
     *             representation to be parsed
     * @return     the integer value represented by the argument in decimal.
     * @exception  NumberFormatException  if the string does not contain a
     *               parsable integer.
     */
    public static int parseInt(String s) throws NumberFormatException {
	return parseInt(s,10);
    }

    /**
     * Returns an <code>Integer</code> object holding the value
     * extracted from the specified <code>String</code> when parsed
     * with the radix given by the second argument. The first argument
     * is interpreted as representing a signed integer in the radix
     * specified by the second argument, exactly as if the arguments
     * were given to the {@link #parseInt(java.lang.String, int)}
     * method. The result is an <code>Integer</code> object that
     * represents the integer value specified by the string.
     * <p>
     * In other words, this method returns an <code>Integer</code>
     * object equal to the value of:
     *
     * <blockquote><code>
     * new Integer(Integer.parseInt(s, radix))  
     * </code></blockquote>
     *
     * @param      s   the string to be parsed.
     * @param      radix the radix to be used in interpreting <code>s</code>
     * @return     an <code>Integer</code> object holding the value
     *             represented by the string argument in the specified
     *             radix.
     * @exception NumberFormatException if the <code>String</code>
     * 		  does not contain a parsable <code>int</code>.
     */
    public static Integer valueOf(String s, int radix) throws NumberFormatException {
	return new Integer(parseInt(s,radix));
    }

    /**
     * Returns an <code>Integer</code> object holding the
     * value of the specified <code>String</code>. The argument is
     * interpreted as representing a signed decimal integer, exactly
     * as if the argument were given to the {@link
     * #parseInt(java.lang.String)} method. The result is an
     * <code>Integer</code> object that represents the integer value
     * specified by the string.
     * <p>
     * In other words, this method returns an <code>Integer</code>
     * object equal to the value of:
     *
     * <blockquote><code>
     * new Integer(Integer.parseInt(s))
     * </code></blockquote>
     *
     * @param      s   the string to be parsed.
     * @return     an <code>Integer</code> object holding the value
     *             represented by the string argument.
     * @exception  NumberFormatException  if the string cannot be parsed 
     *             as an integer.
     */
    public static Integer valueOf(String s) throws NumberFormatException
    {
	return new Integer(parseInt(s, 10));
    }

    /**
     * The value of the <code>Integer</code>.
     *
     * @serial
     */
    private int value;

    /**
     * Constructs a newly allocated <code>Integer</code> object that
     * represents the specified <code>int</code> value.
     *
     * @param   value   the value to be represented by the 
     *			<code>Integer</code> object.
     */
    public Integer(int value) {
	this.value = value;
    }

    /**
     * Constructs a newly allocated <code>Integer</code> object that
     * represents the <code>int</code> value indicated by the
     * <code>String</code> parameter. The string is converted to an
     * <code>int</code> value in exactly the manner used by the
     * <code>parseInt</code> method for radix 10.
     *
     * @param      s   the <code>String</code> to be converted to an
     *                 <code>Integer</code>.
     * @exception  NumberFormatException  if the <code>String</code> does not
     *               contain a parsable integer.
     * @see        java.lang.Integer#parseInt(java.lang.String, int)
     */
    public Integer(String s) throws NumberFormatException {
	this.value = parseInt(s, 10);
    }

    /**
     * Returns the value of this <code>Integer</code> as a
     * <code>byte</code>.
     */
    public byte byteValue() {
	return (byte)value;
    }

    /**
     * Returns the value of this <code>Integer</code> as a
     * <code>short</code>.
     */
    public short shortValue() {
	return (short)value;
    }

    /**
     * Returns the value of this <code>Integer</code> as an
     * <code>int</code>.
     */
    public int intValue() {
	return value;
    }

    /**
     * Returns the value of this <code>Integer</code> as a
     * <code>long</code>.
     */
    public long longValue() {
	return (long)value;
    }

    /**
     * Returns the value of this <code>Integer</code> as a
     * <code>float</code>.
     */
    public float floatValue() {
	return (float)value;
    }