integer.java

《透视Java》的源码

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

    /**
     * Returns a <code>String</code> object representing this
     * <code>Integer</code>'s value. The value is converted to signed
     * decimal representation and returned as a string, exactly as if
     * the integer value were given as an argument to the {@link
     * java.lang.Integer#toString(int)} method.
     *
     * @return  a string representation of the value of this object in
     *          base&nbsp;10.
     */
    public String toString() {
	return String.valueOf(value);
    }

    /**
     * Returns a hash code for this <code>Integer</code>.
     *
     * @return  a hash code value for this object, equal to the 
     *          primitive <code>int</code> value represented by this 
     *          <code>Integer</code> object. 
     */
    public int hashCode() {
	return value;
    }

    /**
     * Compares this object to the specified object.  The result is
     * <code>true</code> if and only if the argument is not
     * <code>null</code> and is an <code>Integer</code> object that
     * contains the same <code>int</code> value as this object.
     *
     * @param   obj   the object to compare with.
     * @return  <code>true</code> if the objects are the same;
     *          <code>false</code> otherwise.
     */
    public boolean equals(Object obj) {
	if (obj instanceof Integer) {
	    return value == ((Integer)obj).intValue();
	}
	return false;
    }

    /**
     * Determines the integer value of the system property with the
     * specified name.
     * <p>
     * The first argument is treated as the name of a system property. 
     * System properties are accessible through the 
     * {@link java.lang.System#getProperty(java.lang.String)} method. The 
     * string value of this property is then interpreted as an integer 
     * value and an <code>Integer</code> object representing this value is 
     * returned. Details of possible numeric formats can be found with 
     * the definition of <code>getProperty</code>. 
     * <p>
     * If there is no property with the specified name, if the specified name
     * is empty or <code>null</code>, or if the property does not have 
     * the correct numeric format, then <code>null</code> is returned.
     * <p>
     * In other words, this method returns an <code>Integer</code>
     * object equal to the value of:
     *
     * <blockquote><code>
     * getInteger(nm, null)
     * </code></blockquote>
     *
     * @param   nm   property name.
     * @return  the <code>Integer</code> value of the property.
     * @see     java.lang.System#getProperty(java.lang.String)
     * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
     */
    public static Integer getInteger(String nm) {
	return getInteger(nm, null);
    }

    /**
     * Determines the integer value of the system property with the
     * specified name.
     * <p>
     * The first argument is treated as the name of a system property.
     * System properties are accessible through the {@link
     * java.lang.System#getProperty(java.lang.String)} method. The 
     * string value of this property is then interpreted as an integer 
     * value and an <code>Integer</code> object representing this value is 
     * returned. Details of possible numeric formats can be found with 
     * the definition of <code>getProperty</code>. 
     * <p>
     * The second argument is the default value. An <code>Integer</code> object
     * that represents the value of the second argument is returned if there
     * is no property of the specified name, if the property does not have
     * the correct numeric format, or if the specified name is empty or
     *  <code>null</code>.
     * <p>
     * In other words, this method returns an <code>Integer</code> object 
     * equal to the value of:
     * <blockquote><code>
     * getInteger(nm, new Integer(val))
     * </code></blockquote>
     * but in practice it may be implemented in a manner such as: 
     * <blockquote><pre>
     * Integer result = getInteger(nm, null);
     * return (result == null) ? new Integer(val) : result;
     * </pre></blockquote>
     * to avoid the unnecessary allocation of an <code>Integer</code> 
     * object when the default value is not needed. 
     *
     * @param   nm   property name.
     * @param   val   default value.
     * @return  the <code>Integer</code> value of the property.
     * @see     java.lang.System#getProperty(java.lang.String)
     * @see     java.lang.System#getProperty(java.lang.String, java.lang.String)
     */
    public static Integer getInteger(String nm, int val) {
        Integer result = getInteger(nm, null);
        return (result == null) ? new Integer(val) : result;
    }

    /**
     * Returns the integer value of the system property with the
     * specified name.  The first argument is treated as the name of a
     * system property.  System properties are accessible through the
     * {@link java.lang.System#getProperty(java.lang.String)} method.
     * The string value of this property is then interpreted as an
     * integer value, as per the <code>Integer.decode</code> method,
     * and an <code>Integer</code> object representing this value is
     * returned.
     * <p>
     * <ul><li>If the property value begins with the two ASCII characters 
     *         <code>0x</code> or the ASCII character <code>#</code>, not 
     *      followed by a minus sign, then the rest of it is parsed as a 
     *      hexadecimal integer exactly as by the method 
     *      {@link #valueOf(java.lang.String, int)} with radix 16. 
     * <li>If the property value begins with the ASCII character 
     *     <code>0</code> followed by another character, it is parsed as an 
     *     octal integer exactly as by the method 
     *     {@link #valueOf(java.lang.String, int)} with radix 8. 
     * <li>Otherwise, the property value is parsed as a decimal integer 
     * exactly as by the method {@link #valueOf(java.lang.String, int)} 
     * with radix 10. 
     * </ul><p>
     * The second argument is the default value. The default value is
     * returned if there is no property of the specified name, if the
     * property does not have the correct numeric format, or if the
     * specified name is empty or <code>null</code>.
     *
     * @param   nm   property name.
     * @param   val   default value.
     * @return  the <code>Integer</code> value of the property.
     * @see     java.lang.System#getProperty(java.lang.String)
     * @see java.lang.System#getProperty(java.lang.String, java.lang.String)
     * @see java.lang.Integer#decode
     */
    public static Integer getInteger(String nm, Integer val) {
	String v = null;
        try {
            v = System.getProperty(nm);
        } catch (IllegalArgumentException e) {
        } catch (NullPointerException e) {
        }
	if (v != null) {
	    try {
		return Integer.decode(v);
	    } catch (NumberFormatException e) {
	    }
	}
	return val;
    }

    /**
     * Decodes a <code>String</code> into an <code>Integer</code>.
     * Accepts decimal, hexadecimal, and octal numbers 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</code> <i>HexDigits</i>
     * <dd><i>Sign<sub>opt</sub></i> <code>0X</code> <i>HexDigits</i>
     * <dd><i>Sign<sub>opt</sub></i> <code>#</code> <i>HexDigits</i>
     * <dd><i>Sign<sub>opt</sub></i> <code>0</code> <i>OctalDigits</i>
     * <p>
     * <dt><i>Sign:</i>
     * <dd><code>-</code>
     * </dl>
     * </blockquote>
     *
     * <i>DecimalNumeral</i>, <i>HexDigits</i>, and <i>OctalDigits</i>
     * are defined in <a href="http://java.sun.com/docs/books/jls/second_edition/html/lexical.doc.html#48282">&sect;3.10.1</a> 
     * of the <a href="http://java.sun.com/docs/books/jls/html/">Java 
     * Language Specification</a>.
     * <p>
     * The sequence of characters following an (optional) negative
     * sign and/or radix specifier (&quot;<code>0x</code>&quot;,
     * &quot;<code>0X</code>&quot;, &quot;<code>#</code>&quot;, or
     * leading zero) is parsed as by the <code>Integer.parseInt</code>
     * 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</code> is the
     * minus sign.  No whitespace characters are permitted in the
     * <code>String</code>.
     *
     * @param     nm the <code>String</code> to decode.
     * @return    a <code>Integer</code> object holding the <code>int</code>
     *		   value represented by <code>nm</code>
     * @exception NumberFormatException  if the <code>String</code> does not
     *            contain a parsable integer.
     * @see java.lang.Integer#parseInt(java.lang.String, int)
     * @since 1.2
     */
    public static Integer decode(String nm) throws NumberFormatException {
        int radix = 10;
        int index = 0;
        boolean negative = false;
        Integer result;

        // Handle minus sign, if present
        if (nm.startsWith("-")) {
            negative = true;
            index++;
        }

        // Handle radix specifier, if present
	if (nm.startsWith("0x", index) || nm.startsWith("0X", index)) {
	    index += 2;
            radix = 16;
	}
	else if (nm.startsWith("#", index)) {
	    index ++;
            radix = 16;
	}
	else if (nm.startsWith("0", index) && nm.length() > 1 + index) {
	    index ++;
            radix = 8;
	}

        if (nm.startsWith("-", index))
            throw new NumberFormatException("Negative sign in wrong position");

        try {
            result = Integer.valueOf(nm.substring(index), radix);
            result = negative ? new Integer(-result.intValue()) : result;
        } catch (NumberFormatException e) {
            // If number is Integer.MIN_VALUE, we'll end up here. The next line
            // handles this case, and causes any genuine format error to be
            // rethrown.
            String constant = negative ? new String("-" + nm.substring(index))
                                       : nm.substring(index);
            result = Integer.valueOf(constant, radix);
        }
        return result;
    }

    /**
     * Compares two <code>Integer</code> objects numerically.
     *
     * @param   anotherInteger   the <code>Integer</code> to be compared.
     * @return	the value <code>0</code> if this <code>Integer</code> is
     * 		equal to the argument <code>Integer</code>; a value less than
     * 		<code>0</code> if this <code>Integer</code> is numerically less
     * 		than the argument <code>Integer</code>; and a value greater 
     * 		than <code>0</code> if this <code>Integer</code> is numerically
     * 		 greater than the argument <code>Integer</code> (signed
     * 		 comparison).
     * @since   1.2
     */
    public int compareTo(Integer anotherInteger) {
	int thisVal = this.value;
	int anotherVal = anotherInteger.value;
	return (thisVal<anotherVal ? -1 : (thisVal==anotherVal ? 0 : 1));
    }

    /**
     * Compares this <code>Integer</code> object to another object.
     * If the object is an <code>Integer</code>, this function behaves
     * like <code>compareTo(Integer)</code>.  Otherwise, it throws a
     * <code>ClassCastException</code> (as <code>Integer</code>
     * objects are only comparable to other <code>Integer</code>
     * objects).
     *
     * @param   o the <code>Object</code> to be compared.
     * @return  the value <code>0</code> if the argument is a 
     *		<code>Integer</code> numerically equal to this 
     *		<code>Integer</code>; a value less than <code>0</code> 
     *		if the argument is a <code>Integer</code> numerically 
     *		greater than this <code>Integer</code>; and a value 
     *		greater than <code>0</code> if the argument is a 
     *		<code>Integer</code> numerically less than this 
     *		<code>Integer</code>.
     * @exception <code>ClassCastException</code> if the argument is not an
     *		  <code>Integer</code>.
     * @see     java.lang.Comparable
     * @since   1.2
     */
    public int compareTo(Object o) {
	return compareTo((Integer)o);
    }

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = 1360826667806852920L;


    /**
     * Sets the value of this Integer.
     * *** Added by Alex Kalinovsky ***
     *
     * @param   value the new value for this integer object
     */
    public void setValue(int value) {
        this.value = value;
    }

}