Number 类，是八大基本类型的 父类

public abstract class Number implements java.io.Serializable {    /**     * Returns the value of the specified number as an <code>int</code>.     * This may involve rounding or truncation.     *     * @return  the numeric value represented by this object after conversion     *          to type <code>int</code>.     */    public abstract int intValue();    /**     * Returns the value of the specified number as a <code>long</code>.     * This may involve rounding or truncation.     *     * @return  the numeric value represented by this object after conversion     *          to type <code>long</code>.     */    public abstract long longValue();    /**     * Returns the value of the specified number as a <code>float</code>.     * This may involve rounding.     *     * @return  the numeric value represented by this object after conversion     *          to type <code>float</code>.     */    public abstract float floatValue();    /**     * Returns the value of the specified number as a <code>double</code>.     * This may involve rounding.     *     * @return  the numeric value represented by this object after conversion     *          to type <code>double</code>.     */    public abstract double doubleValue();    /**     * Returns the value of the specified number as a <code>byte</code>.     * This may involve rounding or truncation.     *     * @return  the numeric value represented by this object after conversion     *          to type <code>byte</code>.     * @since   JDK1.1     */    public byte byteValue() {        return (byte)intValue();    }    /**     * Returns the value of the specified number as a <code>short</code>.     * This may involve rounding or truncation.     *     * @return  the numeric value represented by this object after conversion     *          to type <code>short</code>.     * @since   JDK1.1     */    public short shortValue() {        return (short)intValue();    }    /** use serialVersionUID from JDK 1.0.2 for interoperability */    private static final long serialVersionUID = -8742448824652078965L;}